BigBalla95

I am going to do a compression test on my 95 coupe. I want to know if that will tell me what the problem is. I am doing this because my car is overheating and I have done everything I can think of. I have also tried things that you all have told me as well.

scorp508

Has your coolant gone down? Are there exhaust bubbles in the radiator?

BigBalla95

The coolant has gone down and my oil filler cap smells liks gasoline.

scorp508

Probably not a good sign then with disappearing coolant. You've probably got a bad gasket or head as you said. I would pull the plugs and look to see which one has an antifreeze smell to it or looks wet. It might not be completely obvious so to be honest I'd probably just pull the heads at this point and replace BOTH gaskets to make sure I was good as new on both sides. :cheers:

BigBalla95

I have been told I need to get the heads [ miked? ] to be sure they are not cracked or whatever. What is the exact term? Is this expensive? Is this something a dealer must do , or can I take the heads to a local shop?



[Modified by BigBalla95, 7:50 PM 1/5/2004]

pipe

If yur gonna take the heads off take em to a local machine shop and have them Magnafluxed it will show under a special light if any of the heads are cracked. If not your lucky and maybe just have a bad head gasket. It wouldn't hurt to maybe have a slight surface cut to help insure straightness and a good seal when you put them back on. Make sure you keep everything in order so you can put it back together the same way it came apart AND GOOD LUCK

VetteTech81

Before you pull the heads...

I would first if not done already pressure test the cooling system and check for any possible external leaks.. you may not see them unless it is pressureized..

Second there is a test kit to test for a blow head gasket or cracked head.. it uses some type of chemical and a little bulb and you put it over the fill of the radiator on resivor in this case whith the car running and up to running temp. if the solution changes color you have a blown head gasket or cracked head it I believe it basically tests for Hydro Carbons in the coolant... alot of shops have this test equip. and it will make sure you are not wasting your time pulling the heads.. it would suck to take them off find out there ok put them on and still have aproblem somewhere elese and waste all that time..
-Rick

scorp508

Thats good stuff to have. :yesnod:

JAKE

I just sat here and type a long response trying to help you only to have the Forum tell me that the Title to you post is too long.

When I went back to shorten the response title, all my typing was gone; NOW I HAVE TO DO IT ALL OVER AGAIN.

This is the second time this has happened and it's about time it gets fixed. If the Original Title is too long, why then does it even get used/posted in the first place?

The Forum should alert the poster/responder that the title is too long so all the typing won't be in vain or at least not delete the response simply because the original title is too long.

Who can correct this "bug"?

Jake

1MoorTym

Jake I know how you feel this has happened to me on several occasions. The reason the first one gets posted, in this case the originators is because its not too long, but when you reply to it additional characters get added to the subject such as "Re:" and the user's name of the post to your replying to. This is what kicks the length verification problem. This is no help to you now, nor can I fix it, but thats what causes it.

The mods (web master) should be able to setup the code to either truncate the subject field automatically when it goes over a certain length or gracefully warn you BEFORE you lose your response, preferably before you type anything so you can shorten the subject field yourself. I mean they check the length when you click on post, they should do it when you click on reply. There's a few ways of correcting this, lets see what they come up with.


[Modified by 1MoorTym, 5:30 PM 1/5/2004]

JAKE

Thanks for giving this problem such quick attention.

Jake

JAKE

Okay, here we go again.

No, a compression test will not specifically identify the problem. What it will do is narrow down the possibilities.

If one or more cylinders checks low, it could be any of the following: bad/worn ring(s), valve not seating properly, leaking head gasket, warped head, warped block or some of those in combination.

The first thing I'd do is a coolant system pressure test. You can get a tester from AutoZone, they may rent them for free. Pressurize the radiator (which will also pressurize the rest of the coolant system), and see if it holds pressure. If not, you've may a gasket leak somewhere.

I tend to forget which engines GM designed NOT to have coolant flowing through the intake manifold. If yours is that way, it could only the head gasket.

Unless the engine has severely over-heated at one time or another, I'd say that the chance of the head or block being warped/cracked is remote; possible but remote.

If a cracked head is a concern, unfortunately they have to be removed to be checked. Zyglo testing will show if one or both are cracked; I don't believe you can magnaflux aluminum.

The good part is that aluminum is easily repaired and if it's only warped, surfacing the head will correct this. Surfacing will cause the compression ratio to increase some; how much depends on how much metal has to be removed to give you a true surface again.

The block deck can be checked with a straight edge. If warped; well, that means pulling the entire engine.

If the compression test shows all the cylinder to be within acceptable limits - say no more than 10% between the highest reading and the lowest - Good News. You're over-heating cause lies elsewhere.

I'm sure you've done the basics already - checking for debris in front of the radiator blocking airflow, properly working fan that activates when it should, thermostat not sticking shut (I had one fail to open on me several months ago); properly working water pump; no air in the system; proper mixture of anti-freeze and water (no less that 50/50 to maintain boil-over protection and proper lubrication of the water pump; radiator hose(s) not collapsing; ignition timing not retarded, etc.

Let me know if any of this helps and keep me posted.

Jake

BigBalla95

I have bled the system of air from the brass screw on top of the thermostat housing and after the engine gets to running temp and then overheats there is an abundance of air in the system again. then i will bleed the system again , then there will be more air in the system.

0ski_dwn_it

No a compression test will NOT tell the whole story. Ask me how I KNOW. :rolleyes:


I can tell you what will though. A leakdown test. Before monkey-farting (tech term :D ) around with coolant pressure etc. Get yourself a leakdown tester from Summit. 60 beans. Perform the leakdown and record the values. Anything over 6%, most gages are set at 100psi, so anything over 6psi loss is not acceptable for a race type engine. One could extend this to 10-12 for a street setup, but future tests should be performed to ensure the problem is not progressing.

With this test it will tell you where your leaking also. if you have your rad cap off, you will see bubbles in the rad (head gasket leak), If you hear it coming out the intake, through throttle body (intake valve), hear it out the exhaust (could be tough with cats etc - exhaust valve), hear it out the oil filler (rings).

This way of testing an engines condition is a million times better than compression tests. I wasted an entire summer with my stock 350 doing these comp. tests. All came out +/- 2 psi cylinder to cylinder, did a leakdown and found a few of them 20%+ leakdown. Bingo. I no longer have a compression tester :D :smash:


[Modified by ski_dwn_it, 3:30 PM 1/6/2004]

Jet-Jock

Jake, next time it appears to be happening, before you do anything select your entire post and copy it. Then you can temporarily paste it in a text doc. When the text is safe then navigate the browser and if you loose it no worries, just copy from the text file and repaste it in a new reply.

Oh, I would go with the test kit first like mentioned before. At least its a non-invasive confirmation before you get to wrenching. Could save you time and money over the repair.

:thumbs:

Jet-Jock

Isn't there two bleeds, one on the thermostat housing and the other on the throttle body?

BigBalla95

I am not sure but I did bypass my throttle body

dave_85

Leakdown test! :iagree:

One note: disconnect the PVC hose and hose that goes to the TB to isolate
the sound of the air.

loiq

Pulling it all apart (if that need to be done) should be the last step. Make sure you perform some or all of the tests above until you determine what the problem is. It may save you time and money in the long run. Ask me how I know.

Just my .02! :D

Strick

What did the spark plugs look like? A cylinder with water or coolant in it will produce a very clean plug compared to the others.