I looked at a rough MkIV GTI with a 24V VR6 and got sucked in by it starting right up with fresh coils, idling well, and not making any weird tailpipe smoke. Somehow I forgot to pull the dipstick before I bought it. Messing with it after getting home I find the oil was milkshake, coolant clean.
Tonight we did what I interpret is the best leakdown test I could do limited by the tools I have. The engine was cold because I drained the milkshake oil so it couldn't be started. There was rusty water in the plug holes so I blew that out. I pulled plugs and rotated to TDC. My baby compressor couldn't hold 100 PSI in the cylinder so I set it to 50 PSI. At 50 PSI with my little 0.5 CFM ~1.5 liter "tire fill" compressor humming full tilt each cylinder held 49+ PSI. Is it correct to measure what it can hold with the compressor running? There were no bubbles out of the coolant fill, and there was no apparent hissing anywhere.
If I did it wrong educate me. If I did it right, where is the water getting in the oil? Is the oil cooler really that likely?
You can have a cracked head and get perfect compression/leakdown numbers. I had a mazda 6 that cracked the head between a water jacket and the timing cover, and compression and leakdown tests were both great. Only indication (besides the coolant in the oil) something was wrong was I couldn't pull a vacuum on the cooling system.
ETA: also if the coolants been in the oil for any significant amount of time your bearings are probably junk.
I have heard the the common place on the VR6 for oil and coolant to mix is the oil cooler.
Leakdown testing only tells you about cylinder sealing, nothing else. You're not testing the system that failed.
I'd be very suspicious of the oil cooler if it has one. Especially if the last time the coolant was changed was "nineteen ninety-never"
Is the oil cooler failure endemic to just the VR6, or is it a more widespread VAG oil cooler failure risk?
For the OP, maybe try a coolant pressure tester to pressurize the cooling system and see if you can hear air leaking near the oil cooler?
In reply to Brotus7 :
If there is fluid mixing, it's generally the cooler. It is faaaaar more likely for a cooler to corrode through than a nice broad gasket.
One normally sees this as a failed transmission oil cooler, but engine oil coolers do it too.
This is not VWAG specific, but "everything on the road" specific.
In reply to Brotus7 :
I dont know the answer to that. It is info I got second hand from someone with a VR6 with the same problem. Their research said that the oil cooler was the probable culprit.
Agreed on the oil cooler being the most likely on a stock car.
To be clear, that's not an engine oil cooler. It's actually designed to get the oil up to temp quicker for emissions purposes. And they can fail.
Not sure which VR6 you have, but take a look at this. Head gasket failure can happen in a lot of ways. A leak at the pink box would cause the oil to be a milkshake because it is allowing water into the oil drainback passage from the head, but you wouldn't see oil in the coolant, nor would you see white smoke/steam at the tailpipe. A leak at the blue box you would likely see white smoke, and get milkshake AND oil in the coolant. A leak at the green box you would just have external water leaking with none of the traditional head gasket symptoms listed above.
Brotus7 said:
Is the oil cooler failure endemic to just the VR6, or is it a more widespread VAG oil cooler failure risk?
Many engines have the same problem. If there is an oil cooler/warmer, it's likely not going to last forever. They're usually aluminum, and when you get one side hotter than the other, they can only take so many expansion/contraction cycles before they crack.
In reply to Curtis73 (Forum Supporter) :
Not on a VR6, but I have had a head gasket leak (DOHC 3 liter Taurus) leak compression into the valley, with no coolant loss/pressurization. Sounded like an exhaust manifold leak.
The funny part is, the guy's buddy insisted that we were lying because "that's impossible". Sure, pal, get a length of heater hose and snake it down there and listen for yourself.
Blowing a chunk of the head gasket into the valley was a common failure mode on Grand National engines, too. No coolant issues but they would burn copious amounts of oil to go along with the low compression. Buick head bolt pattern has huge gaps on the sides, this is why the Stage II blocks had six extra bolts per head. I assume the intake manifold torqued to 40ft-lb levers the heads up on that side, since it never happened on the exhaust side.
I'm still betting on oil cooler first, here. If you can remove the cooler while keeping it connected to coolant, you can verify this with a cooling system pressure tester, if you want to be sure.
In reply to Pete. (l33t FS) :
Agreed. Oil cooler first. I also had an IH Comanche 152 (forgive the culturally appropriated name) that did the same thing. I heard it ticking right around the exhaust manifold so I replaced the gasket... then I replaced the manifold... I couldn't believe that it could be the head gasket until I put a 3/8" hose in my ear, then pulled the head and saw the trail. It made it past the fire ring and slowly ate away at the gasket (a long way) until it made it to the outside. Take a look at how far it had to go.
We pressure tested the cooling system and it wouldn't hold pressure. Getting to 15 psi took work and fell steadily once you stopped pumping. We couldn't hear where it was going. Ordered an oil cooler and put her to work on putting the car into service position so we can pull the cooler tomorrow.
Most common actual hg failure on a vr6 is on the coolant galley outboard to #1 (lower left in curtis picture) usually the head corrodes and causes it.
