Leaking head gasket visual clues

[fasterlaster]

This is my first post to the forum, unfortunately not under the best circumstances. My wifes Suburban suddenly started to belch white smoke last Monday. A few cell phone calls later it's sitting in the driveway with strict orders to stay in bed till the dr comes to see it. Here is what I have discovered for some background.

I drove it to work, and it is eating coolant at about 1gal per 50 miles. Some of that is most likely from the cooling system expelling it as the coolant temperature (viewing the dash gauges) will bounce between about 170-270 and when that hot the cap will let out some pressure. When completely warmed up or driving on the interstate the white exhaust is not seen, however slowing to a stop and letting it idle for even just a few seconds, brings back the white cloud. The cloud does not appear till the engine is a little bit warm, but it does happen quite quick. Pulling the oil filler cap I can see pulses of what appears to be water vapor, and the radiator overflow tank line seems to have a pulse. I put a coolant pressure test on it of 17psi, but did not see a loss of pressure. I did not leave it on for a long time only about 30 minutes, but in that time did not see any loss of pressure. I did this test with both a cold engine & a warmed up one, with the same results.

My diagnosis was a blown head gasket (or worse, a head or block crack). Tonight I finally got the heads off and did not see a obvious area for the combustion chamber and coolant system to mix. I have also questioned the thermostats operation with the large fluxuation of coolant temperature (or would a head leak cause this). I did find one area on the #2 cyl that seemed to be a bit torn, but could not swear that I did not damage it when taking the heads off and out, which finally gets me to my question......

What sort of visual clues should I look for on the head or block that might indicate a very mild leak? Any other suggestions re: the head replacement.

[john8662]

Check the heads for cracks.

You'll likely find some small short cracks on a few cylinders between the valves, these are not bad.

The cracks that are bad are those that start at a valve and continue accross the combustion surface of the head.

Some gaskets are harder to detect failure. What kind of gasket was on it? There is a gasket that's made of a softer metal like material, that you get you scrape off (but easily) off the deck and head. The other is a plastic/paper type gasket that usually comes off whole and retains it's form.

Anyways, look for any rings on the cylinders on the gasket that could have dislodged itself from the surrounding material. The usual suspects are on the ends of the gaskets. There is a hole in the gasket for coolant, it has a small amount of material separating that hole from the ring on the gasket. This material moves, and then the ring moves, and you got a blown gasket.

These spots will be beside cylinders 1,2,7,8

Check for pitting on the deck surface in these areas as well.

The temperature swings are a sign, as well as the coolant loss. I do doubt that you've got a cracked block or coolant mixing with oil, the smoke was likely blowby.

The cracking block thing is more common on '97+ engines where cracks get into the cylinder walls leading to water consumption. But, it can happen, just differently.

good luck.

[twaddle]

Hi Jason,
It sounds like most of the coolant loss is happening when the engine is running and being expelled out of the expansion tank cap or radiator cap.

Is the white smoke on initial driving and then clears after a short while? If so the coolant probably enters a/the cylinder/s when the engine is not running but very hot, and appears as white smoke when the engine is initially fired up.

Is there any difference in color on the tops of the pistons, sometimes if enough coolant gets into a cylinder the carbon on the pistons can be cleaned off or at least reduced. Was there a piston that was wet with fuel, sometimes if a cylinder is loosing compression due to a blown gasket the unburnt fuel will lie on the piston. Also look down the exhaust ports for differences in color or damp areas compared to the other ports.

Also look for "blackened" areas between each cylinder sealing ring and any water port/hole on the head gaskets,block and heads, this can show where exhaust gas has been blowing by, the gasket does not have to be split or torn to be leaking.

Any signs of cracks (look for very fine cracks as well as the larger ones) on the heads? Look between the valves and the pre combustion chamber area as this is the most common area for damage.

Let us know what you findings are.

Good luck

Jim Twaddle
Biggar, Scotland

[ronniejoe]

Sounds like the coolant system is being pressurized by combustion gases. Do you have any coolant in the oil?

[Robyn]

Hello and welcome to the forum
We just lost one of our Suburbans to this very thing.
Ours is a 94 with 200K plus miles on it.
If you have driven it much you have probably contaminated the oil with antifreeze.
My recommendations are to yank the engine out and tear it down.
Very good bet that you are going to need a set of heads and very well may need to deck the block (Machine them smooth and flat).
The work involved to do heads in the truck is a pain.
Its a good days work to get the engine out on the ground but well worth the trouble so a top quality job can be done.
If the oil has been contaminated you need to get the pan drained ASAP and dont run the engine any more.
Everything needs to be flushed including the oil cooler and lines to get any antifreeze out.
When ours went it happened at home and I knew what it was and parked it and drained the coolant and the oil quickly.
The pan had about 3 quarts of coolant in it.
You are most likely going to find that you have had a head gasket failure.
These gaskets will weaken and the composit material around the water ports will fail followed by the Stainless steel "fire ring" and then its over.
Ours was losing a small amount of water every month for quite a while which raised a red flag but I waited till it went all the way.
I am in the process now of getting it back together.
Good luck
The folks here can help a bunch
Robyn

[fasterlaster]

Check the heads for cracks.

You'll likely find some small short cracks on a few cylinders between the valves, these are not bad.

I took a quick look and found the little cracks you mentioned between the valves of #2 & #8, but nothing else.


Some gaskets are harder to detect failure. What kind of gasket was on it? There is a gasket that's made of a softer metal like material, that you get you scrape off (but easily) off the deck and head. The other is a plastic/paper type gasket that usually comes off whole and retains it's form.

I was lucky enough to get the soft metal gasket ;( That plus the fact I missed that ground wire on the rear of the even cyl head caused me to quite mess up that gasket.


Anyways, look for any rings on the cylinders on the gasket that could have dislodged itself from the surrounding material. The usual suspects are on the ends of the gaskets. There is a hole in the gasket for coolant, it has a small amount of material separating that hole from the ring on the gasket. This material moves, and then the ring moves, and you got a blown gasket.

These spots will be beside cylinders 1,2,7,8

Check for pitting on the deck surface in these areas as well.

I'll know more when the gasket is scraped off, but it appears the block deck and the head surface are in very good shape, with verry little carbon.


The temperature swings are a sign, as well as the coolant loss. I do doubt that you've got a cracked block or coolant mixing with oil, the smoke was likely blowby.

The cracking block thing is more common on '97+ engines where cracks get into the cylinder walls leading to water consumption. But, it can happen, just differently.

good luck.

thanks, I'll need the luck.


Hi Jason,
It sounds like most of the coolant loss is happening when the engine is running and being expelled out of the expansion tank cap or radiator cap.

Is the white smoke on initial driving and then clears after a short while? If so the coolant probably enters a/the cylinder/s when the engine is not running but very hot, and appears as white smoke when the engine is initially fired up.


It very likely could be loss from the cap, just hard for me to tell. The white smoke will start about 30 seconds from stone cold and will continue the entire rest of the time. It just "appears" to go away at highway speeds, but is back with a vengence when the engine settles down to idle. Reving the engine does not however cause the smoke to go away, just gets much heavier .


Is there any difference in color on the tops of the pistons, sometimes if enough coolant gets into a cylinder the carbon on the pistons can be cleaned off or at least reduced. Was there a piston that was wet with fuel, sometimes if a cylinder is loosing compression due to a blown gasket the unburnt fuel will lie on the piston. Also look down the exhaust ports for differences in color or damp areas compared to the other ports.

Also look for "blackened" areas between each cylinder sealing ring and any water port/hole on the head gaskets,block and heads, this can show where exhaust gas has been blowing by, the gasket does not have to be split or torn to be leaking.

The piston tops all looked to my eye consistant and actually quite free of carbon other than a dusting. It sure sound more and more like a head gasket (I hope)


Sounds like the coolant system is being pressurized by combustion gases. Do you have any coolant in the oil?

The oil appears to have moisture mixed with the oil, but I have not had an analysis done on the oil.

Thanks everyone for the tips, After I can take a much closer look at the engine and get the deck cleaned up I'll report back with anything I find.

[ronniejoe]

If there's coolant in the oil, it may be a cracked block...

[fasterlaster]

Well, between the schedule of baseball/t-ball and normal life, it took quite a while to get this thing back together. After pulling off the heads and inspecting the block and heads as good as possible, I determined to just replace the head gaskets and thermostat and make a go at it. Last night I finished getting it all back together and low and behold it started right up. The white smoke is gone, and idle is smooth. I still will need to replace a few exhaust gaskets that didn't come with the gasket kit, but other than that it's all ready. It kept the temp right about 190 on my trip to work (40 miles) and ran like a top. I think I might have a small diesel leak, but will have to track that down when it isn't raining.

Thanks to everyone for the help and suggestions. I'm happy and mobile again (well my wife is happy she doesn't have to drive my 66 VW anymore)

[Patrick m.]

my head gasket blew at #2 cyl, but it filled the cylinder with coolant. It seems you were lucky.
Hope it stays that way.

[Robyn]

Good to hear you got your rig fixed.
I am still working on ours. Got 4 of the 8 little ponies back in their stable this afternoon.
Just about have all the rest of the parts to finish the beast.