As I was moving my rolling pile of scrap some folks call a 928 back into the garage after yet another day of bodywork on it last night, I noticed a lot of steam coming from the exhaust pipe. So I go down to the parts store today and pick up a compression gauge. It was a pretty decent one that threads into the spark plug hole. So I start checking the compression as per the instructions on the tool and everything seems fine until I get to cylinder #6 and it shows 105 which is a stark contrast to the other 7 which are 160 and higher. Other notable things are the presence of what I think is oil everywhere. Some of the spark plugs are covered in it. It's in the intake, and just seems to leak everywhere. It's also in the overflow bottle for the radiator so I'm thinking a head gasket is shot. My question is how does a car with a functional water pump and temp gauge blow a head gasket? How much of an inattentive idiot do you have to be to not notice your car seriously overheating?

So I'm thinking it's either a head gasket or bent valve, but most likely it's the head gasket. I guess this means the engine gets to come out. What do you people think?

 

The lack of compression could indicate a blown gasket. I've heard about putting some oil into the bore and trying the test again, so see if its rings or the gasket causing low compression.
If the car has only been started to move it a short distance, then condensation can accumulate in the exhaust, and cause a lot of steam. The same can be said for the oily spark plugs, if your valve stem seals are not brilliant, then oil can seep into the combustion chamber while the car is standing.
Ben

 

I agree that the low compression on one cylinder is not a good sign, but don't jump to conclusions. As stated above running an engine (any engine) for short periods of time and never fully warming up can result in significant condensation everywhere; intake system, cylinders, crankcase oil, exhaust. Do you have any reason to think you may have a bent valve? If there is reason to suspect that an event caused a bent valve then I would be concerned, but if it just the compression test I would run the engine, to get it fully up to operating temperature, determine the running performance including water temperature and any misfire. Retest the compression on the one low cylinder. I have seen low compression in these situations that was due to a flake of carbon on the valve seat that disappeared by running the engine.

 

Unless I am missing something, I would think that something else is wrong as Jhowell37 said that there is oil in the coolent overflow bottle. This would indicate to me at least that either a) the oil cooler in the radiator is cracked, or b) an oil jacket in the head is cracked. I dont see how else the oil could get into the radiator fluid...I am thinking that it maybe that the head gasket is blown too, but just a thought. best of luck

 

I agree, sounds like it is time for a chem test.

 

headgasket blew, no blown valves though, but when the headgasket let all the excess pressure from the cylinder into the coolant system it popped a hole in the oil cooler in the rad,

that is my guess, though I can tell you that you have no bent valves, if you did you would have 0 PSI on 1 cylinder.

 

Try a cylinder leakdown test. You get to hear where the air is going. In fact, some of the compression gauges you buy today have a quick-disconnect fitting on them that's perfect for the diagnostic task without spending on a leakdown test. Bring the suspect cylinder up to TDC on the compression stroke. Lock the crank if you can. Apply some low-pressure air to the cylinder through that hose, starting off at, say, 25 PSI. Listen in the oil filler for air flow. Listen at the intake, and at the exhaust pipe. And at the coolant reservoir. It's OK to go up to full compressor pressure if the crank is locked in position, either car in gear or with the flywheel lock used for the timing belt replacement. Air in the intake or exhaust usually points to a bent valve. Air noise from the filler neck means rings are leaking. Air from the coolant reservoir means a headgasket leak. If you find a noise you suspect, do the same test again on a known-good cylinder to make sure that the noise you hear from your 'suspect' cylinder really is abnormal.

Do NOT try to lock the crank with a breaker bar or wrench for a pressure test. If you misjusdge TDC or the wrench slips or moves at all, there's a risk that the stored energy in the cylinder under pressure will THROW the wrench at you or through some valuable part of the car.


Let us know what you discover with this relatively simple test.

 

Make sure to use the hand brake if you decide to lock the engine by placing it in 5th gear.

 

I didn't really think there was a bent valve, I just mentioned it for good measure. As far as adding some oil to the cylinder, I don't think that's necessary as enough leaks into it already. The oil in the coolant overflow coupled with the low compression makes me think it's head gasket. It would really suck if I had to spend the money not only on the parts and labor to replace a head gasket but a radiator as well. Garage construction starts next week, that will go up fast. Then I can move all the other crap out of the small garage on the side of the house and I can really tear into this thing.

 

due to the block and head gasket design a blown head gasket would not under normal circumstances allow oil into the coolant,

I am not saying that it is not possible, I am just saying that it is highly unlikely.

but I do second the motion for a leakdown test, no need to listen in the intake or exhaust, and when you do it with the piston at TDC make sure it is on the compression stroke.

 

a blown head gskt is more likely to give coolant in oil rather than the opposite but its possible. White 'smoke' is also a sign of a blown gasket as the combustion chamber has coolant in it.

Doing a leakdown test will verify the issue and once you remove the head you'll know for sure; gasket being the lesser of the block and or head being cracked.

 

the way the 928 engine is designed with its open block design and how his compression test results occoured unless his head gasket has split in another location it will be the rad, which takes a whole 30 minutes max to take out and test.

 

Sorry, I missed the oil in the coolant overflow on my first read. I agree with others that head gasket leaks "typically" result in coolant in the oil, not the other way around. But then the low compression doesn't fit with a radiator leak unless there is more to this story. Definitly do not start tearing heads off until you do the leak down test and evaluate the radiator and maybe a few other things depending on what you discover. You mention oil on the spark plugs and the intake, are these internal meaning spark plug electrode ends and inside the intake system or external?

 

Oil is inside the intake manifold. Specifically, the ends that come off when you simply loosen the hose clamps. It's hard to be precise with the oil on the plugs because that could just indicate a bad valve cover gasket. But I believe a few had oil around the electrode.

 

Almost all 928s have a pool of oil in the intake below the air filter, there is a bend where a nice pool collects. On my 81s it is easy to see,if you have a later modle with a MAF then you have to take out the MAF to see the pool.

Marton