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Old 04-19-2017, 10:47 PM   #1 (permalink)
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My motor is over heating and I cant figure out why

It's a little of a long read but I need some help! I've posted this in the Chevy forum as well in hopes to try and get as much information as possible.

But as the title says. I have an overheating problem. I have a 90' 5.7 tbi motor in my Scout and have had over heating issues for a little while now. My first time running it on the Wheeling with Cops (pics in my thread of the scout with the kid in the seat and hood off) it ran all day right at 210 no problem. I put the hood on and ever since, I've had issues. Both driving and idling with the hood back taken off also.

I've completely tore down my engine and replaced the head gaskets. New intake manifold gaskets (made sure they were installed correctly). Put everything back together and poured antifreeze into the radiator filling it up and let her rip.

I let the engine idle and idle, with no t-stat opening. The engine got to 250 and I turned it off. So I thought, bad t-stat and bought a new one. (On a side note, when I removed the old t-stat it had this weird white slimy substance on the intake side) Boiled them both and the used one seemed to open more than the new one. So I placed the old t-stat back in the engine. Ran it, and same results.

At this time I disconnected the heater hoses (no switch, always flowing), to eliminate things that could be wrong.

So I placed the new one in and once again same results. Upper hose was cold and radiator was cold. Then when I turned off the engine and walla, i could feel water entering the upper radiator hose.

At this point I flushed the cooling system with water so I limited my costs for new antifreeze every spill.

I let things cool down and started it back up again. This time, the t-stat never opened again once my engine was up past 225. While the engine was running I had water coming out of the overflow tank but the radiator and upper hose were cool to the touch.

I then said screw it and removed the t-stat all together. Temp got up around 210 and then the fans kicked on. Temp went right down to 180 and never came back up as long as the fans were running. I let it idle for several minutes and came back to find the temp got even lower to 160.

I turned off my fans and revved up the engine (1,500-2k) to 210 and then turned on the fans. The engine temp stopped climbing and sat very still. I let off the throttle and it went back down to 180.

Thinking it was now a water flow problem, I decided to purchase an aluminum high flow water pump. I just installed it today. At the same time I installed the "newer" t-stat with two holes drilled into the sides of the lip and once again filled the engine up with water via the radiator and started it up.

Temp went up to 200 ish, sat for a little while and then kept climbing and climbing, even with the fans on. Went up to around 250 and I shut it off. I felt the upper hose and I could feel little thumps inside the hose (im assuming bubbles, I think due to just running water its boiling in the engine?? Cap was on the radiator at this point. And cap is a 1.1 cap)

For whatever reason I kept the key on and let the fans run while the engine was off. I let the temp gauge go down to 200 and started the engine back up. The temp went down to 180 real fast, then stopped. Then within 2 mins, it climbed up past 210 and just kept climbing.

I repeated the aforementioned step several times with the same results. On one occasion I started the engine and the temp gauge went immediately down to 180 then back up to 210 then it slowly went down in temp to 180. So not sure if that was a surge from the "cool" fluid in the radiator into the engine or what.

While running with these tests, I could very noticeably feel the difference from the upper to the lower hose side of the radiator. The fan closest to the upper hose had warm air blowing through and the fan closest to the lower hose had cooler air coming through. The radiator was also hot on the upper side and cool on the lower side. So I believe I'm getting good enough air flow through the radiator. But I didn't have the borrowed temp gun to find out the temp difference in the two sides, to even see if its cooling it enough. But I could put my hand on the lower side tank and keep it there without it getting too hot for me to touch.

Tomorrow I plan on running a pressure test on the radiator again. And using a vacuum system to try and see if I have a very stubborn air pocket somewhere in the system.

I'm running out of options here. New head and intake gaskets, new t-stat, water pump and I recently placed a bigger radiator thinking I needed more volume.

WTF is going on here?? How does one check to see if the engine has a clogged passage? If I put water down the t-stat opening in the intake, how will I know that the water coming out is enough of a flow?

Could a bad ECM make the engine want to run hot? Its timed properly but I'm just trying to think of all options here.

Thanks for any help guys!
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Old 04-20-2017, 03:23 AM   #2 (permalink)
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Hi, I've read your post a few times and can't help thinking that you have a water flow/air pocket problem. Sounds weird that it has only happened since putting your hood back on, but maybe just coincidence. Can't speak for anyone else but I've NEVER been able to feel much difference between the in and out sides of the radiator. Sure, the in will be hotter, but the out is usually too hot to touch for long as well. I have had issues in the past where fluid can't/won't get to the thermstat and so it just doesn't open. I suggest you try filling the engine with fluid via the thermo' housing, that way you will know you have fluid to that point, and then replace the thermo' and housing then fill the radiator up. That way you should be confident that you have a full engine and radiator. Alternatively you can fill the engine through the radiator, wait a few hours or overnight, and see if the fluid level goes down. If it goes down it will be an indication that maybe fluid isn't getting past your thermostat very easily or quickly and this maybe tricking you into thinking that everything is full when you just fill from the radiator. Which is what you should be able to do but for some reason maybe it isn't working in your case.
Anyway, thats my .02 cents worth, hope it helps. Trying to fix overheating prob's can be a PITA and sometimes there is no blatantly obvious reason. Looking forward to hearing how you solve it
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Old 04-20-2017, 04:11 PM   #3 (permalink)
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Sounds like air in the system. Other ideas...I know you said you put in a larger radiator, was it new? I chased a cooling problem for a year on one of my Scouts, finally bought a new aluminum radiator and fixed the problem. Also you said the motor ran cooler without the hood on, might be a little extreme, but I put a volvo puller fan on the hood of my crawler and it solved all my heating issues.
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Old 04-21-2017, 12:27 AM   #4 (permalink)
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Yea radiator was brand new 3 row aluminum radiator with two 12" electric fans. That would be a BIG extreme for me to put a fan in my hood. You can see pretty much straight through the engine compartment while standing at the front tires. I believe I have enough air escaping the hood area, if not Ill install hood louvers for a last resort.


Today I used an airlift system. The instructions say minimum shop air pressure is 90psi. I have 120psi easy. I ran the tool and I could only get the psi on the dial to just above 15psi, the instructions say to get it it 22-26psi. So I don't know if it's my shop air just not getting enough air out to create a better vacuum or what. After closing the ball valve the needle sat still for roughly 20 seconds as instructions state it should. However shortly there after the needle began to drop slowly. I then filled the engine with water using the system. I repeated the vacuum process 3 times and each time the vacuum gauge read less and less on the max psi before I shut the valve. Radiator was then filled.

Started it up again and my temp is above 210 and my fans didn't kicked on, (bad connection I think, that I'll have to fix) and while fixing the connector, I looked around and my radiator cap had water coming out from under it. It was tight and so I guess I'll have to replace that bastard again and see what's going on.

So, while letting the engine cool down, I drained the radiator again and placed a pressure tester on it. I could hear a watery bubble sound coming out of the engine compartment at 5psi. Looked and my upper radiator hose was leaking. Tightened it up and continued pumping. I got up to 20psi and no other leaks. I squirted the engine with soapy water and couldn't see anything additional leaks.

The instructions stated there could be a pressure drop due to the engine cooling, so I disconnected it and waited another hour. I then retested the pressure tester and when I got to 15psi, my lower radiator hose at the water pump began to leak water. Tightened that up and continued pumping. Once I got to 20psi my lower radiator hose at the radiator began to leak water. I touched the clamp and then it definitely began to leak air. Tightened it up and then re-pressurized the system to 20psi. Went inside and changed for work, 15-20min, checked the gauge and what ya know, still at 20psi.

I'm hoping that was the hold up but Ill keep you posted.
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Old 04-21-2017, 07:01 AM   #5 (permalink)
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You are fighting the air leaks. If you were able to get 20 lbs of pressure on the system you should be good now. As a suggestion I would not put more than 15 lbs on a cooling system though. Try to pull a vacuum on it again and see what you get also.

Does your system have an overflow can that it can pull back out of when its cooling down?
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Old 04-21-2017, 12:20 PM   #6 (permalink)
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You are fighting the air leaks. If you were able to get 20 lbs of pressure on the system you should be good now. As a suggestion I would not put more than 15 lbs on a cooling system though. Try to pull a vacuum on it again and see what you get also.

Does your system have an overflow can that it can pull back out of when its cooling down?
I just put a vacuum on it today and once again only got to around 17/18psi on the gauge. Then my shop air kicked on. Not sure if it was a coincidence or not but. I shut the valve and let the air build back up and then turned the valve back on. The psi doesn't continue to climb.

It held steady above 15psi though. Yes I do have an over flow tank.
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Old 04-21-2017, 02:33 PM   #7 (permalink)
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Alright so I have some strange symptoms...

I can now idle in my garage at 225 on the gauge. At idle is either on the 225 notch or a needle width above. I raise the rpm to about 1k. And the needle drops to the lower side of the 225. And sometimes to about half way to 210.

I said screw it and drove her out of the driveway and around the blocks a few times. Held steady at 225. I then went up the hill to see what she'd do. While cruising into town the temp was just below 210. Then when I finally hit the hills it climbed up to just above 225 near the top of the climb and held steady.

I then went back down hill and temp began to drop. Went down to 200 or just below. Keep in mind my throttle is either off or just going enough to continue the vehicles momentum down hill. While nearing the bottle of the hills, I looked at my temp gauge and it was going back up!! It went above 250 and I pulled over. I sat for about 10 seconds and went forward at a normal acceleration. The temp went down immediately! It went to 210. Then once again continuing down hill the temp went back up to 250. I pulled over and sat for about 5-10 secs and then accelerated down hill. The temp went down to 225! I have a video of the second circumstance, I'll post in a little bit.

But WTF IS GOING ON?!?! bad t-stat? Waterpump? What!?!

It did have the check engine light on half way up the hill and for the remainder of the drive. Checked it when I got home and I forgot to plug my knock sensor back in. duh... but plugged it back in sitting in the garage and temp has been at 225 for 10+ mins at idle.
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Old 04-21-2017, 04:21 PM   #8 (permalink)
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Here's the video of the temp change when I pulled out and drove.

https://youtu.be/lX0fIu6hPhE

And after reading the Chilton's manual concerning the check engine light, I readon't on things that could cause over heating. It stated loose belt among other things. So it got me thinking, any of you with this similar motor is this satisfactory for tension?

[IMG][/IMG]
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Old 04-22-2017, 09:39 PM   #9 (permalink)
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Do you have a shut off valve to your heater core that is shutting off water to the heater when you are not using it? Whats your temps with the heater running and does it put out heat?
Since we crawl, I run about 1,500 rpms when I do, I'd make sure your water pump is at least 30% overdriven.
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Old 04-23-2017, 03:50 PM   #10 (permalink)
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Do you have a shut off valve to your heater core that is shutting off water to the heater when you are not using it? Whats your temps with the heater running and does it put out heat?
Since we crawl, I run about 1,500 rpms when I do, I'd make sure your water pump is at least 30% overdriven.
During this whole shit storm of over heating, I've disconnected my heater system to help narrow down issues. Normally though it doesn't have a valve to stop the flow. When I last ran it, it was blowing hot air.

I was looking at the conversions for pulleys to rpm's. And that's what made me look at my tensioner pulley. Would getting a shorter belt do anything for the rotations of the pulleys or not? My thought is that a shorter belt would take less time to go one complete rotation. Which would make things move faster?? Or am I just thinking wrong?
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Old 04-23-2017, 04:06 PM   #11 (permalink)
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the length of the belt does nothing for the speed of the pulley's, only the diameter of the pulley's. Either changing the crank pulley to a bigger one, or the water pump pulley to a smaller one will make the water pump spin faster.

One thing to look at would be the amount that the belt touches the pulley. If there is not enough engagement between the two there can be slippage. This isn't usually a problem on the water pump though, unless is very minimal, you run into that issue more on the power steering and possibly the alt. Do you have a pic that shows the belt routing?
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Old 04-23-2017, 04:30 PM   #12 (permalink)
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What are you basing the temp off of just the gauge? Have you checked the acurccy or it? What does the ECM temp sender read?

And when above 210* are your fans on? Did see you state your fans running but the one time you remove the thermostat. Are you fans on at right temp and spinning correct direction?

Also what codes do you have??
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Old 04-23-2017, 09:12 PM   #13 (permalink)
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Is the engine bone stock? Was there anything done to it that is causing it to run lean at times? Its been a longtime since I played with a Chevy engine of that era but I recall the PCMs were moody and would do strange things with even minor engine or drivetrain changes, particularly changes that would increase airflow in or out of the engine and would cause them to run lean.
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Old 04-24-2017, 12:19 AM   #14 (permalink)
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the length of the belt does nothing for the speed of the pulley's, only the diameter of the pulley's. Either changing the crank pulley to a bigger one, or the water pump pulley to a smaller one will make the water pump spin faster.

One thing to look at would be the amount that the belt touches the pulley. If there is not enough engagement between the two there can be slippage. This isn't usually a problem on the water pump though, unless is very minimal, you run into that issue more on the power steering and possibly the alt. Do you have a pic that shows the belt routing?
OK, so shorter belt won't make things spin faster. I feel I have a good amount on tension on the belt system. And assuming the designs on the tensioner pulley means that I'm within spec of the correct amount.

Here is a pic from the build up. It's the same routing currently.

[IMG][/IMG]


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What are you basing the temp off of just the gauge? Have you checked the acurccy or it? What does the ECM temp sender read?

And when above 210* are your fans on? Did see you state your fans running but the one time you remove the thermostat. Are you fans on at right temp and spinning correct direction?

Also what codes do you have??
I am basing the over heating based on my dash gauge. I just borrowed a laser temp reader today and my ecm connection on the driver side head seemed to be slightly lower, to close to what the gauge read based on what part of the adapter I pointed it at.

My fans are on when the gauge reaches around 210. If I remember correctly my fans have a 195 on and 175 off. I'd have to research that though. I've had some recent connector issues with my fans, today the temp went above 210 and they didn't turn on, I turned off the truck but left ignition on and a few seconds later the fans kicked on.

The one time I remove the t-stat they did turn on around 210 on gauge and stayed on til the temp went down to around 165 ish on gauge. Fans are definitely going in the right direction. Other than the knock sensor not being plugged in, I havnt had any codes on my OBD1 system.

I used the temp gun today and pointed it at various places in the engine compartment. The t-stat never read above 190 even though the gauge sat at 225 most of the time. My driver side radiator to passenger side radiator was constantly 20+ cooler from intake to output. So radiator is doing its job.

What I found interesting was my passenger side head was around 180-200 in the front portion between the forward exhaust dump and the center dump, where the same portion to the rear was anywhere from 250-280+ at times. But it never was below 230. Here's video.

https://youtu.be/bjfxH2Oh05I

https://youtu.be/6rkXgwaR138

My driver side head in the same spots was 210 and 225.

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Is the engine bone stock? Was there anything done to it that is causing it to run lean at times? It’s been a longtime since I played with a Chevy engine of that era but I recall the PCMs were moody and would do strange things with even minor engine or drivetrain changes, particularly changes that would increase airflow in or out of the engine and would cause them to run lean.
Far as I know the engine is bone stock. I got the truck for free from auto shop back in the day, who got the truck from a local college auto shop for a donation. The odometer had 2k on it. My dad and I rebuilt it. Somewhere I misplaced the original ecu, so I grabbed another one from PNP. Now that I think of it, I hope I grabbed the right serialized ecm. I know there's two types, and I believe I did my research and bought the correct version. What would the wrong ecm do to the motor?

No cam mods or injector mods, a higher flow electric fuel pump, a cold air intake system. And other than that nothing... prior to pulling my heads I looked at the spark plugs and they all looked fine. Another note, when I first took apart my engine I always had this oil leak at the second head bolt back from the front, on the drivers side. It appears to be coming out between the head and block. I replaced my head gaskets and ran it with no leaks. Now since I drove it I saw oil on the floor. It seems to be leaking again and it looks to be leaking slightly more than it did before. Not sure what's going on there.

Thanks for the questions and comments guys. I'm getting pissed enough, I may have to take it to a shop to see WTF is going on. I hate to do it but if I nor them can't figure it out, the scout may need another engine or something... I definitely don't have the funds for that shit right now.
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Old 04-24-2017, 09:22 AM   #15 (permalink)
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Is the temp sensor for the gauge in the stock location?

Where is the temp coming from to run the fans? Same as gauge or ecm?
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Old 04-25-2017, 09:51 PM   #16 (permalink)
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I would add a second temp gauge to compare to the dash gauge. Is your water Pump turning the right way. Some belt configurations have different rotations.


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Old 04-25-2017, 10:30 PM   #17 (permalink)
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If I didn't know better, I'd say your water pump was turning in the wrong direction, or your thermostat was installed backwards .


Back in the 90s when I worked in a shop I remember the chebbys had water pumps that looked identical but the fins were on backwards on some due to the routing of the belt, so some turned clockwise, some turned counter clockwise, and I recall seeing the wrong pump installed more than once, and on some you could put the belt on two different ways and it still fit perfectly but the pump spun backwards .


I would have already set the whole thing on fire by now .




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Old 04-26-2017, 08:56 PM   #18 (permalink)
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I would add a second temp gauge to compare to the dash gauge. Is your water Pump turning the right way. Some belt configurations have different rotations.
I went and bought anot her temp sender unit, maybe my old one is fried... I'm going to have to test the ohms on both to see if they're consistent or not.

I just swapped out to a high flow reverse flow water pump, in hopes the original water pump on the engine was bad, or not pushing enough or the wrong way. But both water pumps were reverse rotation pumps due to the serpentine belt system. I havnt taken off the backing plate on either pump though to verify impellers though.

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Is the temp sensor for the gauge in the stock location?

Where is the temp coming from to run the fans? Same as gauge or ecm?
The temp sensor for the gauge is in the head, between cylinders 1 and 3. ECM is up by thermostat on intake.

The temp for the fans is on head between cylinders 6 and 8.

On another note... I swapped out to a 180 t-stat and while running that my fans never turned on. I messed with my fan switch and presto... it came apart if it's not one thing it's another.

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If I didn't know better, I'd say your water pump was turning in the wrong direction, or your thermostat was installed backwards .

Back in the 90s when I worked in a shop I remember the chebbys had water pumps that looked identical but the fins were on backwards on some due to the routing of the belt, so some turned clockwise, some turned counter clockwise, and I recall seeing the wrong pump installed more than once, and on some you could put the belt on two different ways and it still fit perfectly but the pump spun backwards .

I would have already set the whole thing on fire by now .
My t-stat has been installed correctly. Spring down. I'll check the fins on my original water pump and see what it looks like. But it should be for a serpentine belt system. Back ports blocked on the intake manifold for the reverse water pump.

Hell, I've thought about getting a 70's style intake manifold gasket for shits and giggles, just to see if opening that back port will do anything.

I'm starting to think, I have a wrong part installed somewhere. Maybe my motor and it's accessories arnt a 1990, has the truck was.
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Old 04-26-2017, 08:59 PM   #19 (permalink)
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The serpentine belt system was what I was speaking of .

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Old 04-29-2017, 05:07 AM   #20 (permalink)
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Checks?

Have you noticed any more air bubbles coming into the water hose?

Have you done a compression check or a leak down check on the engine?
Same symptoms from several engines and all have been either cracked heads or block.

Just a thought.
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Old 04-30-2017, 09:07 AM   #21 (permalink)
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Any more air bubbles? I did a pressure test and I found some leaks in the hoses and tightened the clamps up.

Havnt done a compression or leak down test. That's probably what I'll end up having to do next.

Well that's promising, cracked head or block. I just had my heads check prior to the replacing the gaskets, so that leaves the cracked engine. I hope your wrong . If that's the case, the scout won't be on the trail for years.

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Originally Posted by Roboter3 View Post
Have you noticed any more air bubbles coming into the water hose?

Have you done a compression check or a leak down check on the engine?
Same symptoms from several engines and all have been either cracked heads or block.

Just a thought.
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Old 05-01-2017, 10:42 PM   #22 (permalink)
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Well that's promising, cracked head or block. I just had my heads check prior to the replacing the gaskets, so that leaves the cracked engine. I hope your wrong . If that's the case, the scout won't be on the trail for years.



Don't count on a cylinder head NOT being cracked just beacause you just paid someone to check them .

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Old 05-05-2017, 12:18 AM   #23 (permalink)
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Don't count on a cylinder head NOT being cracked just beacause you just paid someone to check them .

It is hard to find good help these days. But the business I took the heads to is a reputable business that working on engines and heads is all he does. I believe him when he said they weren't warped or cracked. But yes you never know.
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Old 06-08-2017, 06:28 PM   #24 (permalink)
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Not sure if this is relevant, but... Is it possible you have a gasket (head or intake) installed backward or mis-manufactured (missing a hole or hole in wrong place)?

That might explain the hot spot on the one cylinder head.
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Old 06-09-2017, 06:36 PM   #25 (permalink)
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Not sure if this is relevant, but... Is it possible you have a gasket (head or intake) installed backward or mis-manufactured (missing a hole or hole in wrong place)?

That might explain the hot spot on the one cylinder head.
I showed the temps to my buddy and he said my intake manifold gasket was on backwards for that head. I disagreed as I know I placed them both on the correct way.

I'm trying to install a 2 speed Volvo fan right now. So hopefully it does the trick and it was an air flow problem. If not then I'm towing it to my buddies shop to have them diagnose it for me. As I'm fed up with it.

Kinda hoping he says I need a new motor. May end up forcing me to get something else in there
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