Chip's Diablo Compression and More!

Ok, so the car has been running fine with the exception that I apparently had a loose fan wire which was making the fan come on intermittently. One time on the interstate in traffic without realizing it, the water temp was pretty hot before I could pull off. No coolant overflow, etc but it was hot. So I fixed the wire and then occasionally when driving since the water temp will be at the normal 85 or so and then shoot up to about 95-100 when stopped but then cool back down some when moving.

So not too long back I (and I am very, very paranoid in general) noticed what appeared to be a very slight sheen in the coolant overflow tank. Not discolored just like a drop of sheen. Of course the first thing that popped into my head based on the whole situation was maybe the head gasket is failing. So I bought a $110 digital compression tester a few weeks ago and just got around to using it. The results are (psi):

 

7 8 9 10 11 12

(160) (168.5) (145.5) (156) (153.5) (162.5)

 

 

6 5 4 3 2 1

(162) (160.5) (154) (158.5) (150) (167.5)

 

 

Car had been brought to operating temperature and shut down before doing the test. The only thing I did not do was push the gas pedal down or open the throttle. Each test was essentially 7-8 engine rotations. Lowest 145.5 and highest 168.5 are right next to each other but within about 13.9%. Anyone want to chime in and give me some opinions on the numbers?

 

I'm highly considering pulling the engine myself and replacing all the gaskets and doing some other odds and ends while i'm in there. (Ceramic coating the headers, powder coating the intake manifold and cam covers, cleaning up the engine bay in general). Thanks!

I wanted to make a new test with the gas pedal down and open throttle for more precise numbers.

 

if the engine head gasket is leaking, water will bubble in the coolant overflow tank and the engine will use the water, so you have to refill it often.

if it has been leaking for some time, you can also see it on the spark plug. if the engine is filled with blue liquid coolant, you can see that on the spark plug, it will be a little blue.

compression test from my engine :

 

I will try to do it again with the throttle open. Your values are around 180-190s psi it looks like. I remember a thread by member AB years ago and his values were around 125 psi. I don't know what that all means. No discoloration on the spark plugs. I do leak a little coolant but that is usually from the pipes near that radiators for me. Haven't noticed anything on the dipstick or any issues during my last oil change.

 

Higher numbers, better condition if there's anyone who stands out, it may be: burned valve, or there may be a crack in the cylinder head between the two valves broken piston ring or leaking head gasket.

when you make compression test: all spark plug must be pulled out, full throttle and turn the engine until you get the highest number for each cylinder on your tester.

Thanks! I just forgot full throttle.

I should also ask....I pulled the #18 fuse in the passenger footwell (injection system I think). The T, U relays in the engine compartment fuse box along with fuses 32, 32. And then the relay and fuses behind the passenger seat. I wanted to be safe but what fuses and relays do you pull? I also disconnected the main power wire that goes into the distributor.

I don't foresee the throttle open changing the results much, if any. You can put a little oil in each cylinder and test again, to see if the numbers go up. This would point to where the compression loss is coming from, cyl walls, or valves. They also make a kit that you can use, to pressurize the cylinder, and if there is a head gasket leak, you can observe the bubbles in the coolant tank live, without the car running.

 

 

Thanks! Yeah I google'd and saw that throttle open only leads to higher numbers really so that probably won't tell me too much more. Also, I have never seen any bubbles in the coolant tank. I do need to try the wet compression test which I would have done yesterday but realized too late that I didn't have any funnel long enough to get the oil in there. I guess my main question is that I'm wondering if there are any light bulb ideas that pop into anyone's head by seeing them? Is 168.5 right next to a 145.5 a cause for concern? It doesn't seem like there is any blatant result like "yep the head gasket is failing" or anything.

 

Maybe there is some blockage in one or both of the radiators. I am running Mobil 1 10W30 which is a little lower than what most people run so maybe that is something (first time I had tried Mobil 1 in here).

 

I had a valve adjustment a year and a half ago as well.

If the numbers are in close variation across the board, you're good.

 

As for your 145psi cylinder, that is down. It is more than a minor deviation, but not a bad deviation. For example, my STi had a blown ringland, three cylinders were around 150psi and the damaged piston was under 100psi.

 

Also, you can put a tiny amount oil in the cylinder (google it) to help swell the rings and get a more true compression reading.

 

Thanks Nick. I will try to do a wet compression test in the near future.

http://www.blockchek.com/

 

Will tell you if you're getting combustion gasses in the coolant and confirm or eliminate the head gasket failure.

http://www.blockchek.com/

 

Will tell you if you're getting combustion gasses in the coolant and confirm or eliminate the head gasket failure.

 

Thanks! I'll check that out

Also, do a leakdown to make sure that it's not your valvetrain.

I will have to look into a leak down tester. Since a just had a valve adjustment last year, wouldn't that have been checked out though? I'm sure it could have changed since but who knows.

also check relays and relay sockets for the fan issue

i chased that issue and found the sockets were corroded