Headgasket- Low compression

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toddrs93

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Hello, I am new to this platform but I am a mechanic who owns my own shop. I do mainly aftermarket performance stuff and I would like to maybe offer some performance packages for this car in the future.

For now though I am jumping into an 02 LS V8 that looks like a blown headgasket. I found it interesting that there seems to be alot of skepticism on here anytime someone mentions a blown headgasket.

This particular car has an intermittent miss under highway speeds that is only sometimes noticeable. It will also overheat after a few days of driving due to loss of coolant and there does not appear to be any leaks.

Also two spark plugs in two side by side cylinders appear wet, and there is rusty discoloration on the bottom of the coils.

Compression test revealed about 20 psi in these two cylinders. Does not appear to be coolant in the oil or vice versa so it does look like a small leak in the headgasket is burning the coolant.

Contemplating a leakdown test to further isolate the issue and confirm 100% that it is a headgasket but I am pretty confident thats it based on what I am seeing.

Anyways thought I would post to get some feedback and hear about other experiences.
 
Failed coils and degas bottle will not give 20psi compression.

If you are a mechanic you should be able to test for combustion products in the coolant. It is not an expensive tool. These cars have a cooling failsafe mode so headgasket seems unlikely. What seems more likely is that the timing chain skipped.
 
SteveSC said:
Failed coils and degas bottle will not give 20psi compression.

If you are a mechanic you should be able to test for combustion products in the coolant. It is not an expensive tool. These cars have a cooling failsafe mode so headgasket seems unlikely. What seems more likely is that the timing chain skipped.
Click to expand...

I missed the compression part!
 
I would guess coils, degas, and timing chain tensioner(s) went -> bent valves -> no compression
 
I'm not sure about the coils. No compression on 2 cylinders would cause the car not to run right. You've turned a v8 into a four cylinder with 2 cylinders extra, so I would guess it wouldn't run very well.
 
Yea interesting engine. So last week when I checked it like I said I got 20psi on the two and then I always try to check a known good cylinder on the engine if possible to get a baseline and to verify my gauge is working properly. So I did that and I got 180psi on another cylinder in the same head. Now forward to today I decided to go ahead and do a leak down test to get more info. I do the one bad cylinder and I get a 20% reading which definitely doesn't go in line with the low compression. 20% is out of spec but probably acceptable. On a cylinder with 20psi I should be seeing like 70% plus leakage. So I do another comp test and now the cylinder reads 198. I test another cylinder and same thing 198. I drive it a while and no miss.

Not sure how that's possible BUT this car was recently purchased at an auto auction. I know how a lot of the auction cars work, people will put all kinds of head sealer in the car long enough to hide the problem and get it through the auction. I bet that's what's going on. Some Rislone or Bars Leak or something is floating around in there doing crazy things.

Also the one cylinder that's had the main problems has a new coil in there. It is different from the other 7 and looks in way better shape. So it appears someone tried to fix and cover up the problem.

At this point though there's no 100% conclusive evidence it's the head gasket or anything else for that matter.

I did a coolant system pressure test and found nothing. I will try a block test soon which is what someone was referring to about sampling the coolant.
 
toddrs93 said:
For now though I am jumping into an 02 LS V8 that looks like a blown headgasket. I found it interesting that there seems to be alot of skepticism on here anytime someone mentions a blown headgasket.
Click to expand...

I don't think anyone is saying that the head gaskets never fail, just that it's unusual for this engine. And the issues that on most engines would point towards a head gasket are most often caused by other problems with this engine.

The failsafe air-breather mode does a lot to prevent warpage and hence a failed head gasket.

Good luck with the work! I'm sure you've seen the standard advice to replace all coils and plugs and take a very close look at the entire cooling system.
 
It seems unlikely but the only way to explain no compression on two cylinders and then compression again is that the timing chain skipped twice. First it skipped to give no compression and then it skipped back to give compression again. I don't see how anything like a stop leak could be doing that. I have never heard of stop leak being able to fix a blown head gasket but I guess it may be possible. Especially where the compression goes to almost zero and then returns to full levels!
 
SteveSC said:
It seems unlikely but the only way to explain no compression on two cylinders and then compression again is that the timing chain skipped twice. First it skipped to give no compression and then it skipped back to give compression again. I don't see how anything like a stop leak could be doing that. I have never heard of stop leak being able to fix a blown head gasket but I guess it may be possible. Especially where the compression goes to almost zero and then returns to full levels!
Click to expand...

Don't see how a chain can skip backwards..... Maybe the initial reading was wrong....
 
I agree it seems highly unlikely but how else would the compression be restored? It is more likely that the readings were wrong. Unless the compression tester was not screwed in fully on those two cylinders and then we have to disregard all compresiion tests. The guage would need to be tested or replaced if necessary. Usually if the compression tester is loose the noise from the escaping gas is enough to clue you in when you get low readings. Even a low reading would cause most people to check to see if the guage was properly installed.
 
SteveSC said:
It seems unlikely but the only way to explain no compression on two cylinders and then compression again is that the timing chain skipped twice. First it skipped to give no compression and then it skipped back to give compression again. I don't see how anything like a stop leak could be doing that. I have never heard of stop leak being able to fix a blown head gasket but I guess it may be possible. Especially where the compression goes to almost zero and then returns to full levels!
Click to expand...

Na like I said I did a comp test and it was low, removed the gauge and put it in another GOOD cylinder which read fine. Then checked the cylinder a second time, and low again. Then removed it again and checked it again a third time and still low. Each time it screwed in just fine and my gauge is just fine.
Then days later it checked ok for whatever reason.

I'm not really talking stop leak, more like hardcore stuff they sell behind the counter at parts stores, such as this:
http://www.hardwareandtools.com/CRC...gle Products&gclid=CKj4ztq3wrMCFYuZ4AodmTMAxw

This crap will float around through the engine and seal stuff up. I know the auction where this car was bought and people do that crap all the time. They take a car in good condition with a blown headgasket, and throw something like that in it and pray it makes it through the auction so they can get there money. Then later down the road, the stuff breaks down inside and the leak reappears.

Anyways it did show oil in the coolant so we are pulling the heads.

One question I had was do these timing chains have a master link or quik link of any kind to take them apart to reinstall? Trying to keep costs reasonable here so no need to replace the existing chains unless alot of wear is visible. I searched and everything seems pretty generic. Theres very little info when it comes to the actual chain itself.
 
toddrs93 said:
One question I had was do these timing chains have a master link or quick link of any kind to take them apart to reinstall? Trying to keep costs reasonable here so no need to replace the existing chains unless a lot of wear is visible. I searched and everything seems pretty generic. There's very little info when it comes to the actual chain itself.
Click to expand...

How many miles? Since you're already there with the chains off why not do a little preventative maintenance and replace the chains and tensioners? Looks like the parts are ~$230 from Tasca.
 
welcome todd.

this is interesting.

not that this would be a suggestion, more of a question, I'm no expert
could it be rings on the cylinders? or how about valve seals? (is it burning any oil)

how much oil was in the coolant, what is the reading of the test? just curious I've never seen or done it before.

hope the head gasket job works for you
 
If you are going to take the chains off, put new chains and tensioners on. The only thing I would consider not replacing would be the sprockets. If this the mileage is high, I would replace the sprockets as well.
 
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