Hey Scotty,
I recently bought a 2002 Yukon Denali with 180,000 miles and automatic transmission with 6.0 L V8. I had it pre purchase inspected by a mechanic and he found a leaking main seal and a knock sensor. But 1 week later...
I looked closer and I have a layer of milkshakey goo on the bottom of the coolant reservoir and a thin layer of it along the inside of the heater hoses. The coolant otherwise looks pretty normal. But no coolant in the motor oil (that I can see.)
No rough idle, no white smoke, no high engine temps, no observed coolant loss, in 100 miles of driving. Oil level hasn't gone down. Runs great, runs quiet, heat works, AC works, zippy on the freeway.
1) What could cause this? Wouldn't a head gasket leak cause bidirectional mixing?
2) Is there a way to detect coolant in oil before it looks funky?
3) Would this be a Bar's Leak candidate?
4) What should I do?
Other details:
No rough idle, no white smoke, no high engine temps, no observed coolant loss, in 100 miles of driving. Oil level hasn't gone down. Runs great, runs quiet, zippy on the freeway. Only engine code is for low voltage to knock sensor. No maintenance records available.
Love this new (to me) rig and want to get at least a few years out of it!
@thejarv
Simply put you need a head gasket replacement and have the heads checked
Let me try to answer your questions and chip in my 2 cents.
1) What could cause this? Wouldn't a head gasket leak cause bidirectional mixing?
It is possible to have it mix both ways, but that depends on where the damage to the head gasket is located. It can fail to allow fluid one way only or both ways. Additionally, the pressure in the cylinders tends to push the oil/fuel out into the coolant versus the other way around from a physics stand point. Engine design can effect that, though.
2) Is there a way to detect coolant in oil before it looks funky?
Sort of. Obviously, if they are mixing in any decent amount, you will see the tell tale signs more readily. But, if the mixing is very minute, you can send your oil off for analysis to have it checked. This is relatively cheap and easy to do during an oil change, and it gives you a report not only of if any coolant is present but other materials/metals as well with general standard metrics to compare to. This can give you a bit better view into the health of the engine in general.
3) Would this be a Bar's Leak candidate?
I wouldn't rush to put a coolant sealant additive into your car's coolant system, especially when you don't notice any dramatic mixing or drop in fluid volume indicating a leak. Most of those sealants are a temp fix and, in the long run, can gum up other parts of the coolant system that are healthy requiring additional parts and labor costs to repair later on.
4) What should I do?
Based on the information provided, while it may still be a minor head gasket issue, I wonder if the car previously has a coolant system or gasket issue that a previous owner repaired the key points, but either they or their mechanic did not fully clean/check the other parts of the system. I am always an advocate of checking/testing the cheapest/easiest routes first before going down repair rabbit wholes. In this case, I would suggest to do the following:
1) Drain the engine oil and the coolant systems.
2) Send the engine oil out for analysis - Google Blackstone Laboratories
3) Methodically go through the coolant system pipes, overflow reservoir, and anywhere else you can check to clean out the gunk you noticed
4) If the gunk can't be cleaned out, replace the part as most hoses and reservoir tanks can be purchased relatively cheaply
5) Run straight water from a hose through the coolant system and flush it out thoroughly. You can also run a flush cleaning additive such as those by Preston or similar too.
6) Replace the engine oil filter, refill engine oil, and refill coolant system with 50/50 compatible coolant for your vehicle
Now drive the car like normal and monitor for any fluid loss/usage or mixing as you have already been doing. If nothing happens, I would guess it was previously fixed. If it occurs again, then you have a more definitely answer that it is likely a head gasket.
While the steps above seem like a lot and complicated, they really aren't and can usually be done with basic tools, a Saturday, and referencing some YouTube videos for guidance. Worse case, you can have a local shop do the same for a couple hundred bucks would be my guess. Either way, well worth it compared to the several hundred to thousand dollars a head gasket repair can run on a car.
@wildbill
First off all, thank you very much for your advice. It is helpful and easy to follow. With this much coolant capacity I realized that between coolant, and contaminated water that it would be a little more hassle than I would like, an oil change place did it for $120 which isn't that much more than 6 gallons of 50/50. Hopefully they didn't bone the job. I did an oil change right after I got the rig a few weeks back so I will put a few more miles on it in case the leak is really small so the lab could get a better sample. I didn't check my mileage but I would say it has had probably 10 hours of running time since the oil change.
I also did a pressure test on the cooling system. Held 15 PSI for 60 minutes. It was raining and I didn't want to leave it unattended overnight. I did a combustion leak test with the blue fluid and the little pump that you insert into the radiator. My truck doesn't have a radiator cap, it is in the expansion tank. It did not change colors, though apparently it is possible with that volume of coolant that it would take a while to be detected with that test, or at least I would imagine that was the case.
At this point I get a fair amount of white colored smoke from the tailpipe at idle only even after the engine is at 195-200ish and not any observed while driving. It doesn't smell sweet to me, I have had coolant leaks in other vehicles so I am pretty sensitive to the smell. But at the same time some of these newer coolants don't seem to smell like the green stuff.
So anyway my thought is to put another 50-100 miles or so on it, then drain the oil and send it off to a lab. Does that sound reasonable?