My jeep has been behaving odd in terms of overheating. It stays cool when you are just crawling along or when travelling at high speeds. If you are going like 20 mph (say while travelling to trail head along secondary trail) it starts to overheat.

Brand new rad last year. Was cooling fine.

These symptoms started late last wheeling season and progressively gotten worse.

At the end of my last trail run, I thought 'maybe it's just low on water', so I stopped by a hose and opened the rad cap to put some water in. At the top of the rad was a layer of oil. Not much, but a thin layer. We put water into the rad (which was not low on water to begin with), which forced the oil out (it was floating on top of course). At the end of it there was not a lot of oil expelled, I'd roughly estimate less than a fifth of a quart, if that.

My first thought was 'blown head gasket'. This is what I've seen in the past with oil in the coolant, BUT - usually when this has happened to me with other vehicles in the past, there was a LOT of oil in the water, and a lot of water in the oil - the tailpipe was puking water vapour. This is not the case here, the jeep is otherwise running fine, and no water vapour is coming out the tail pipe, and no water appears in the engine oil when drained.

So I'm confused.

The other issue is that my buddy says that the 4.0 does not have a direct access between an oil passage and a water passage where the head and block meet, so if there is a problem, it is likely a cracked blocked, not a blown or warped head.

So we are in a quandry because we don't want to spend more time/effort/money tearing the engine apart if the block is blown - it's much easier to simply replace the engine.

Can anyone shed some light on these types of jeep engine problems? Am I looking at a blown or cracked head, or block, or both? Is there something else that could put oil in the water (but not water in the oil) that would cause the symptoms which I have described???? Again, other than heating up, the engine is running fine.

Thanks a lot for all your help, sorry for my mechanical naivette.

Regards,

Chad

is it in a wrangler,cherokee.....
how many miles
did it overheat...240 or better

if its in a cherokee they tend to run hot anyway
if it's got a ton of miles (150,000+) on it replace the head gasket
if you overheated it you could've warped the head or blown the head gasket

if it was me, i'd replace the head gasket and see if it fixes it. i had a cherokee that blew it's head gasket and started filling the crankcase with water. it didn't put a whole lot of oil in the rad. but you could see a film on top

Also if its an automatic trans, I have seen the trans cooler thats in the radiator leak, putting trans fluid into the rad. Just a thought.

If it's in a cherokee, what year is it. I work at a dealership and we have had a lot of late model heads crack between cylinders 3 and 4. Just something to look for. Add dye to the coolant and you will be able to look in the oil cap and see if it's cracked with a uv light.good luck.