Zero10

I hate to start another thread, but while doing some minor work on my car last night, I discovered something disturbing.

While driving my 951 back from New York, just after medicine hat, my car broke down. It had overheated. When I saw the temp light on, I shut the car off, but I have no idea how long it was on for.

Last night, while putting some minor things back together, so I can drive the car out of my garage, I took a quick look at the vacuum lines.

There is one that runs underneath the manifold, pretty much directly over the spark plugs, that was melted to the head.
I previously compression tested the engine, but the battery was mostly dead, and the engine was at about -10C, however I got results of about 70psi on all 4 cylinders.
If the engine got hot enough to melt a vacuum line to the head, should I be worried about having warped the head?
It ran rather poorly on the trip back to Calgary once it was repaired, much worse than it ran before, however I know some vacuum hoses weren't put back together correctly at the volkswagen dealership.

I am already going to be pulling the intake manifold and such changing vacuum lines, and I would like to hear your guys's opinion before I get into it too deep.

The vacuum line, was one of the thin plastic ones, and it had melted to the edges of the spark plug holes. I would imagine this would be one of the hottest parts of the head. The spark plug boot was not melted.

M758

A warped head should result in a leaking headgasket right?

If so do you still have overheating issues?

Zero10

It overheated because the cooling system froze. The block defrosted because it was running, and when driving on the highway I guess the pressure of the water pump when the engine is at 2500RPM, was enough to push a coolant hose off, and all of the coolant in my block poured out all over the highway. I didn't notice right away. I looked down a couple minutes after leaving medicine hat, and the temp warning light was on (the temp gauge doesn't work). I was checking it every couple minutes, since we didn't have any heat, and it was -28C.
I shut it off as soon as I saw the warning light, and coasted off the road.

A warped head should result in a leaking head gasket, that is correct.
I pulled all 4 plugs, they all look fine, but I don't know how else to tell if my head is warped...

Laust Pedersen

That you have uniform compression between cylinders is a very good sign. That it only is 70 psi (vs. a good 145 psi) hopefully is because of the cold temperature and very slow cranking (compression numbers are a function of cranking speed).
At the very least fix the leakage, change the oil, warm it up and repeat the test.

Zero10

Sounds good.
I caught it blowing bubbles around one of the head studs, but that may have been gas leaking down and boiling, I can't tell for sure (it all reeks of gas, since the fuel line leaks).
I'll fix up the fuel line, and fire it up, once it's warm, I'll pull my subaru into the garage, tie the batteries together, and give 'er a go. That way I shouldn't run the battery down too far (the one in the 951 is just about done for).
I'll let you guys know what I find, but I was worrying a lot once I found the melted hose.

Laust Pedersen

That’s one of the beauties of aluminum block and head (without steel liners) with good thermal conductivity, it all expands at the same rate …. except the head-studs.
Having said that, maybe you should just double check the torque of a single head nut. If one is OK then all likely are OK, but if it is too much out of spec, then they all need to be re-torqued, following the proper procedure.

Zero10

If a head stud came loose, I probably blew the head gasket

It was a bad trip, first I learned that the wastegate was disconnected, so I had no boost control, then it overheated, I'll be amazed if the head gasket is alright after all of this.

Laust Pedersen

My point is that aluminum (block and head) expands more than steel (studs) at elevated temperatures, so it is possible that the headgasket got (plastically->non-reversible) squeezed more than normal and you therefore lost a fraction of the clamping force of the studs/nuts on the head when the temperature returned to normal.

Again, the uniform compression numbers is a good indicator for no head warpage and also that the headgasket does not leak (it would be very unusual if all cylinders leak the same amount).

Zero10

Oh, I see what you meant, good point
I can be a little dense sometimes.

Zero10

Well, I took it out for a spin today, I got it back, and started the tear-down, I know most of the vacuum lines are bad, so I started pulling the manifold, intercooler pipes, fuel rail etc. Once I got it all apart, I decided to compression test it one last time. We had duct tape over the intake ports in the head. We removed the duct tape from the #1 intake hole, installed the compression tester, and turned it over... We heard 3 nice loud pops, which was the duct tape popping off of the other 3 intake ports. I found this disturbing, but I removed the duct tape, and turned it over again. The compression test was as follows:
#1: 120
#2: 110
#3: 100
#4: 110
This was with a 'warm' engine, it was not hot, but maybe around 50 degrees celsius. These numbers worry me, shouldn't they be much higher for a '65000' mile engine?... I'm going to contact the people who sold the engine, and see what they have to say. The unreasonable sale price suggests that they were not lying about the mileage (almost 3000 for the engine), but I would like to verify it...

All of the plugs were just buried in soot, since it is running very rich. I have a few bad boost leaks, so this makes sense.
What do you guys think?... I don't think it's head gasket.

hosrom_951

Normal operating temp should be ~90C for the oil and the throttle should be wide open during the compression test......

Zero10

I figure that with the manifold off, it's even better than wide open throttle
I guess it wasn't quite up to temperature, but those numbers still seem pretty low...
Am I safe to rule out the head gasket?

p950nlu

I did a compressioncheck yesterday.
engine has run 200,000km , dont know howe many miles that is
I let the engne warmup för about 5 minutes. I did not have the throttle opened at all, should it be?
I got these readings
1 145 psi
2 120 psi
3 145 psi
4 150 psi

The sparkplug on 2 is more dirty than the others, so something ain't right there
Overall I think that the compession is ok for a 200000km car and 18 years old engine

Peckster

You have a problem on 2. Could be bore, rings, or a valve.

Mike B

A better test to determine engine problems is a leakdown test. Try "leakdown test" on google. Here is one link.

http://www.geocities.com/dsmgrrrl/FAQs/leakdown.htm