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80 w/SBC 350 overheating issues.. (long)

4K views 34 replies 15 participants last post by  MochaMike 
#1 ·
I've been having overheating issues with my junk for several months.
My junk was running around 195*-210* at low RPMs on the street.
When I would go up over a local hill, running at about 45-60mph (3-5k rpm) it would fly up to 250*.

History:
SBC350, Rochester 2 barrell, Rams Horns, 2" pipe into 1 flowmaster 40 series, SM465, D18 on 35s.
Swap was done 20 years ago, but never finished (truck sat for 20 years).
I put in EVERYTHING but the engine.
I've done a bunch of engine work, but nothing major to the block (new main seals & other gaskets).
I did have the heads cleaned up & valves re-seated.
While it was apart, I cleaned out the block, heads & intake build-up with a screwdriver.
I've flusheed it dozens of times.
New points, set timing/dwell, new hoses, & thermostat (180*).
H20 pump was replaced 2 years ago, but then it sat for a year during buildup (less than 200 miles on it).
Radiator out of a 60s vette (came with my project) was pressure tested last year.
Was overheating with the mechanical fan, so I swapped in a taurus fan as a pusher. That didn't work.
Moved the radiator forward, made fan a puller, that didn't work.
Swapped in a custom 4 core I got from Scout Dude... Still overheating.
This week I trimmed 1/2 of each inner fender well, thinking that it was an airflow problem.

Tested it after I did each of the cooling items listed above.
It brought it down a bit, but not enough.
Now it runs at 180*-190* at low RPMS, but goes up to 195* on hot days & 210*-230* on that hill.

This week I'm going to pull the hood off & see if its still an airflow problem.
The 4 core is also kinda narrow & tall, I'm planning on puting a shroud between the radiator & my grill to help channel/funnel air toward the radiator.

I'd like to swap in a new H20 pump as well (currently unemployed=no $$$ right now).

Anyone else have any ideas?
 
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#3 ·
Maybe I didn't think this through enough, but I think you have more of a coolant flow problem than an airflow problem. Above 20mph or so I would think that as long as the rad is big enough you shouldn't need a shroud or fan with the 350 and the rather light 80 without the added heat of a auto.

Do you have a heater, and if so how hot is it blowing? Spring in the rad hose?

How is the oil pressure at startup and when hot?

How fast is it spinning at highway speeds?, what gears?
 
#4 ·
Make sure you are not over advancing the timing. You can advance the timing too far and the engine won't even rattle, Just runs hot. Also make sure the heater hose lines are blocking coolant flow to the heater core. No just looping the heater hose back to the engine. BLOCKED FLOW. :)
 
#5 · (Edited)
That SBC shouldn't be running that hot in that rig, with that much fan on it, and a good thermostat.

I agree that timing is most likely a good place to start, but another is the water pump itself. Take the cover off the back of the water pump, and look and see if the impeller has been dragging or scuffing the cover. A lot of times rebuilt water pumps don't get the impeller pressed on far enough to get some clearance behind the impeller, and then the water pump doesn't pump at capacity.

A lot of good tech here: http://www.flowkooler.com/problems.html?FKSID=b2a5d43818cab7974442a4823670e169
 
#6 ·
ChiScouter said:
Maybe I didn't think this through enough, but I think you have more of a coolant flow problem than an airflow problem. Above 20mph or so I would think that as long as the rad is big enough you shouldn't need a shroud or fan with the 350 and the rather light 80 without the added heat of a auto.
I'm was concerned about the anount of air going through the radiator.
The new radiator is 17"x17" (of core) & the grill is 10" high by 33" wide.
Being 10" high, air is only hitting 10"x17" of radiator (hence the shroud).
Also, before I trimmed the fenders, you couldn't see daylight when viewing the engine from above. I was thinking that even with the fan, at high speed, the front grill/radiator would be the may air flow both in & OUT.

ChiScouter said:
Do you have a heater, and if so how hot is it blowing? Spring in the rad hose?
Yes, very hot & Yes...

ChiScouter said:
How is the oil pressure at startup and when hot?
Yes, can't remember the numbers. I thought it was low & asked a few friends..In the mid 20s at mid Rpms, lower at idle, higher at higher RPms.

ChiScouter said:
How fast is it spinning at highway speeds?, what gears?
4.88 gears, about 3-5k rpms at 55 or 60mph.

Shadow man said:
Make sure you are not over advancing the timing....Also make sure the heater hose lines are blocking coolant flow to the heater core. No just looping the heater hose back to the engine. BLOCKED FLOW. :)
Its at 6* (set & checked it several times).
A friend is suposed to stop by tomorrow, so I might have him help me play with it.
Hose goes from pump to mini radiator for heater & to the intake manifold.
Entire radiator gets hot & my overflow usually boils over.

IHC-6 said:
Take the cover off the back of the water pump, and look and see if the impeller has been dragging or scuffing the cover. A lot of times rebuilt water pumps don't get the impeller pressed on far enough to get some clearance behind the impeller, and then the water pump doesn't pump at capacity.
Did that. Showed it to my parts guy (who I trust).
He said it was fine & put the new one he pulled back on the shelf (that's why I trust him).

I don't think he is wrong, but I probably will change it out (since it is a rebuilt).
Thanks for the link.

I should also mention that before I trimmed the fender wells, the hair on my legs used to get singed (sp?)... :eek:
 
#7 ·
Mike,

1) it's a 5 core, triple pass radiator
2) I told you that you need to make a shroud ON THE FRONT end so that all the air coming through the grill is forced through the radiator. Scout 80's/800's have a small grill and need all the help they can get.
3) Add a std fan shroud for low speed cooling, but above 35 mph, the fan doesn't do the cooling, the wind speed does.
4) As mentioned, timing can cause it to overheat
5) replace yor waterpump...they are cheap and easy enough to replace
6) Are you sure that you're not sucking you lower hose closed? (Does it have a spring in it?)
7) maybe your block is fawked and needs to be hot tanked..I know you flushed it about a dozen times, but sometimes hot tanking is the best answer
 
#9 · (Edited)
i'm betting it's the radiator. you said it was out
of a 60's vette & had been sitting for a long time,
that you had it pressure tested, & farther down
said it was "new"; so i'm a little confused? when
you had it pressure tested was it flow tested as
well? if it is that old it may very well need power
flushed, or rodding out. even if it flows, cooling
tubes may be coated with old anti-freeze & not
dissipating heat. check thermostsat again, if it's
been up to 250 deg. it could be stuck, voiding
anything you've done since then.

edit: re-read, just saw you swapped in a 4-core rad.
what kinda shape was it in?
 
#11 ·
I have the same problem in my 80 with a 350. It has the stock scout radiator and I'm fixin to replace it with an aluminum one and build a shroud.
It would run at 190 all the time then up to 210 on the freeway with 33s and 4.10s. Once I was going around 10mph on the fire roads up in the hills at Stonyford it went up to 240 and bolied over, then bent the tie rod, but that's a different story. This was a summer trip in Nor Cal it gets hot there.

After this trip last year when I have experienced this I vowed to never drive it until I rebuilt it, so I haven't had any cooling problems since because I haven't gone over 20mph since then. :rolleyes:

Other considerations: Fuel mixture too lean?
Right pressure cap on the radiator, if old replace they're cheap
 
#14 · (Edited)
Ya, if I had $200-$400 around I would get a huge new radiator.

Joel used the radiator I got in there now with his Caddy motor with no problems. I just have to do the frontal shroud thing this weekend.

Mech fan is a problem though.
The engine sits forward & low.
With a 13" or 14" fan, I have less than 1/2" clearance of the crossmember.

At this point, I'm praying it's not the engine.
 
#15 ·
Mine is out of a 1969 Cadillac, look for the big old Cads in the junkyard, they all have huge radiators. I cut the core support/shroud out of the Cad, and trimmed it until it fit between my inner fenders, welded on some flanges and bolted it between the inner fenders. Works great. With a radiator that big, I imagine the taurus fan would probably be OK, I just prefer mechanical.

Other than that, make sure you aren't running lean, and check your total timing.
 
#16 · (Edited)
Just like ben w said, check total timing. set it at 36-38 degrees total. my race car is set at 38 total, but it has initial of 18. kinda high for initial, but total is all that matters. especially if your running that many RRRRRRRRR's on the freeway. Shoot, ya might even see more performance, but it is still a chevy. :nuke: :flipoff2: :flipoff2:
 
#17 ·
MochaMike said:
Played with that already.
Did you change carb jets or just turn the idle mixture screws?
 
#20 ·
MochaMike said:
Mixture Screws.
Then all you did is adjust the mixture from Idle to 1200 rpms. You could be lean as hell on the main power circuit and this would cause your heat issues.


Jump into the truck with a spark plug wrench and drive for a mile at 40 to 55 MPH. Push in the clutch and turn off the ignition. Coast to a stop and pull one plug. Let us know how she looked.
 
#22 ·
Took it out around town today for about 30-45 minutes of average driving, some stop & go & cruising at 45mph.

Carb was at 2 turns out, it's about 85* outside.
Engine ran kinda like crap... 1 or 2 backfires & sounded like lots of back pressure when rpms decreased from being high.
About 180-185* most of the time.

I adjusted the carb i 1/4 turn, & ran it for about 5 miles, did notice it seamed a little hotter 195-200.. But I'm not sure if that was from the coolant sitting in the engine for 5 mintues while I adjusted it.

I then adjusted back out another 1/4 turn (at 2 1/2 turns out).
Ran the hill.
It jumped up to about 210* on hill, which I didn't think was too bad.
Its about 3-4 miles running at 55mph & 3k rmps.

Well, after turning off the hill & cruising at 2k rpms/30mph it shot up to 250*+

I thought rochester 2 barrels were good anywhere from 2-4 turns out... :confused:

I think I'll try & scrape some cash together for another h20 pump.
 
#23 ·
Ok,
I took it for another ride after it cooled down.
I refilled the radiator (lost about 1/2 gallon & had a 1/2 gallon in the overflow.)
I forgot to mention that before I did the hill, I discovered that I left the vacuum advance hose off the carb.. :shaking:

Anyways, I checked the plugs, & they looked kinda grey, so I turned the mixture in 1/2 turn.

Drove it pretty hard, didn't go over 190* but I didn't do the hill.

Ran much better, but still sounds like backpressure on decellartion (kinda like "almost" backfiring).
 
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