Best and most decisive way to determine blown headgasket? (vehicle, spark plug, exhaust)

[wheelsup]

My car has been losing a very small amount of coolant over the past few months. Truth be told I don't know when it began because it's such a small amount.

A little history:

Back in June '08 the lower radiator hose blew and the car overheated. Instantly I shut it off when I saw the low coolant light illuminate.

Two months later the radiator cooling fan relay failed, which didn't turn on the fan, and the car also overheated, however it was about 200 yard from my house so I drove home and shut it off.

Those are the two overheating episodes which is why I'm thinking head gasket. No steam has ever been observed, there is no oil in the coolant, it is bright green after being refilled 7 months ago. Although I know that is not a definitive answer yes/no.

Now, back in October I also replaced the other radiator hoses and it was after filling up the coolant level at this point that I noticed it was dropping over time. Slowly.

By slowly I mean over 1500 miles of driving it dropped around 1 cup of fluid or around 1 cm's worth of travel on the expansion tank. Not much.

I ran a compression test and got the following:



The last cylinder has me concerned however it doesn't say "head gasket" immediately.

I was wondering what the best and most decisive method for detecting a bad HG was. More specifically, I'm looking for something that is sensitive enough that would detect a small issue if there was one. I am about to throw some money at this car and would like to know that the engine is holding up at least at this moment.

What tests would you recommend?

1. Block Tester (NAPA)
2. Oil Analysis (extremely sensitive to coolant in oil)
3. Leakdown test (have to get indy to do it, I don't have the tools)
4. Something else I don't know about?

Here is the car, a 1995 Volvo 850 N/A (non-turbo) w/ 148k



Thanks for any ideas!!!

[High_Plains_Retired]

[SIZE=2]You can also test your radiator for presence of combustibles. This can be done in minutes if you have the test equipment or by a garage.
[/SIZE]

[ferretkona]

I would drain the oil and take a look in the oil.
Volvo's aluminum heads can warp if over heated.

Even if you do a head job the engine could seize later.
Many good used motors are available and a exchange is often cheaper than a head job.
My friend (now deceased) owned a Volvo garage. Ken bought a lot of used motors from Thomas Bros in Torrance.

I had my last cars head rebuilt after a blown head gasket. The motor seized on me 8 miles after I picked it up.
The headjob was $1200. The motor being rebuilt cost me $3200 in addition.

[wheelsup]

OK that's with a block tester I believe, around $50 at NAPA, is that the best way? Would it even detect such a small leak?

[wheelsup]

Originally Posted by ferretkona

I would drain the oil and take a look in the oil.

I changed the oil 3 months after the overheating and it looked fine, and it still does. The coolant loss is so low that I don't think it's enough to change the oil color just yet.

[stanman13]

Do you notice an abnormal amount of white smoke (steam) from the tailpipe? By abnormal I mean that it doesn't go away after the engine warms up.

[High_Plains_Retired]

Originally Posted by wheelsup

OK that's with a block tester I believe, around $50 at NAPA, is that the best way? Would it even detect such a small leak?

I believe this test can detect very minute amounts of combustibles in the coolant but I would ask a professional mechanic who has actually done the test. I became aware of this test when I replaced the heads on my 350 c.i. GMC truck and worried that I may not have gotten the new head gaskets down correctly. I bought the test but never used it. It proved to be an unfounded worry.

[Dave_n_Tenn]

I must assume ... the leak (loss of coolant) occurs while not running. Therefore loss of coolant should be visable as white smoke. However assuming it is so small it is not noticeable, maybe a simple application of stop leak? or similar product. After all, the vehicle has 140,000 + miles.

You might try a re-torque of the head bolts. I might also suggest removal of the plugs after run time (cooling system pressurized) ... let sit (24hrs?) and crank the engine without the plugs in a inspect for vapor? water? coolant? at the spark plug holes. If you have a radiator pressurizer might save some time.

[studedude]

Combustion pressure is much higher than radiator pressure. Because of that coolant would get into combustion chamber during intake stroke but combustion gas would get into radiator during combustion. This would cause car to overheat frequently. You say it is loosing small amounts. It is either going to atmosphere or to crankcase. If it is leaking outside of the engine it would show up on ground unless it is leaking out and hitting the exhaust manifold and evaporating. A close look at anything very hot should show evidence. It may be hiding under a heat shield. Others have mentioned water in oil. Small amounts will not change oil appearance but they will show up if you pull dipstick and put several drops on an exhaust manifold. Oil will smoke. If it has any moisture it will boil. It's an old mechanic's trick but then I'm an old mechanic.

I can't see the electrodes on you plugs very well but it appears from the color of the threads on #5 it is running cooler. It may be just the lighting. I would start there when looking for trouble.

[Angelinthedesert]

If you see water droplets on or in the oil on your dipstick, then you have a blown gasket.