Oil in the coolant

[RustyShackleferd]

Hey everybody, I recently bought a non running 1991 2wd comanche with a 4.0L and what I think is an AX-15. I was changing the coolant when I noticed what appeared to be oil leaking back up into my funnel.  After a bit of research this leads me to believe that the head gasket is blown or possibly something worse.  As this is my first time restoring a vehicle any advice would be much appreciated. 

[Green Mesa XJ]

Possible but given it’s a 27 year old vehicle it could be a number of things disintegrating over time, like the rubber on the radiator cap or some form of stop leak.

I don’t know how meticulous the maintenance was by previous owners, best bet is to start with compression testing as a base line, then move on to other tests.
Headgaskets can go on these 4.0 but they are stout engines, they die hard. Could be you need a new gasket but I would test first.

How does the oil look?


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[DirtyComanche]

X2 on looking at the oil.

 

Assuming the oil is okay, I'd fill the cooling system back up and monitor things.  Unless there's something else obviously wrong with the engine.

 

Any ideas why it is not running?

[Marine1Texas]

The pressure of the coolant system would push coolant in to oil before it would allow oil in to coolant system. Check your oil. If you oil does not have coolant in it, than I am thinking something else than a head gasket leak.

However a compression test with spark plug inspecting will see if you have blown or leaking head gasket. Check and smell spark plugs for coolant.

 

I would not doubt it was radiator stop leak added. Many people get heater core leaks and add it to stop it. However it ends up all thru the cooling system.

 

You can always do a pressure test on your cooling system. I bet your heater core leaks and Previous owner added it in.

[shelbyluvv]

Not true at all. My truck has been pushing oil into the coolant for about a year. The head gasket is finally really letting go and I have steam coming out my tail pipe and it smells sweet.

I still have no water in my oil.

[Eagle]

6 hours ago, shelbyluvv said:

Not true at all. My truck has been pushing oil into the coolant for about a year. The head gasket is finally really letting go and I have steam coming out my tail pipe and it smells sweet.

I still have no water in my oil.

 

Makes sense. Oil pressure can be up to 60 psi -- cooling system is 13 or 15 psi, maximum.

[Green Mesa XJ]

Well there are several passage ways besides the combustion cambers/cylinders, a headgasket can leak at any of them. Some Chrysler/Jeep 3.7 & 4.7 owners have documented (meaning repaired under warranty) oil leaks from the headgasket, with no contamination of the coolant and no seal issues with the compression, just oil leaking out from the side of the block at the headgasket.

 

In this case I still would test everything just because it’s unlikely and I have no idea what the OP actually is seeing. A none running vehicle is difficult to diagnosed Online , it may be a mechanic’s special but it can be a novices nightmare. I’ve seen so many young guys and gals get their hands on a older (their age) vehicle and jump the shark trying to fix what was a simple repair.

 

For all we know the engine is toast and locked up.

 

 

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[RustyShackleferd]

Thank you for all the replies, I checked my oil and it looked brand new so my brother and I went ahead and fired it up and it ran great! I will be test driving it tomorrow.  When I bought the truck it had been sitting for a year and the serpentine belt was rotted out and seized.  Also the alternator was blown up, I replaced both of these issues and it seemed to be what the truck needed.  I decided to replace all of the fluids first, when I refilled the coolant without starting the engine, It looked like clear oil was leaking back into my filling funnel.  I replaced the oil prior to the coolant and it appeared that the new oil was leaking up through the radiator into the funnel.  It was a good amount to, not just a couple drops but a steady stream flowing up the side.