what symptoms would a blown head gasket or a cracked head cause? The engine has plenty of power. No one at the advance auto knows what it could be.


BTW The engine is a 4.3L V6 vortec

Ok...here's my two-cents worth. I would try and replace the thermostat again - even though I believe you said you already changed it. You never did say if you have antifreeze/water in the oil which would indicate a blown head gasket. I personally have a 1994 Chevrolet Van conversion with a 5.7L engine, and not too familiar with your engine, but for the 8 or 9 bucks, would try and change the thermostat one more time. I have had bad ones "right out of the box" before, and have even heard of people taking back their "old" ones and putting them back in the box, just to get a refund. Anyways, if I can think of something else, I'll write you back. Bob

Symptoms for cracked head or bad head gasket:

Going from minor to major:

Overheating, especially at idle after a long drive (the leak allows vapors to enter the coolant stream, and bubbles form, blocking coolant flow. At high engine rpm's, the bubbles are flushed out, but at idle the flow is too low, and coolant circulation slows....)

Slow to reach normal engine operating temp at idle. (not sure why this is, but it was the first symptom my mechanic mentioned at the time...)

Coolant loss with no visible leak.

Sweet smelling exhaust with cloudy white billowy quality (indicates leak of coolant to combustion chamber)

May or may not show loss of power (depending on severity of leak)

Possibly coolant in oil or vice versa. Coolant in oil looks milky. Oil in coolant looks scummy. Contaminated oil ruins an engine very quickly. Don't run it this way, if you find milky oil.

In very bad leak situations, when an engine is run (cold start) with the rad cap off, an impressive fountain erupts with each compression stroke.

I had a Celica with a dodgy head gasket. It took me a year to figure out what was wrong. Only symptoms were overheating at idle after long cruise and slow heat up as mentioned above. Also, cruising above 80mph would result in overheat.

Cracked heads and blown head gaskets behave the same way. They're different problems, but have all the same symptoms. When you pull the head to do the gasket, be sure you have the head professionally checked, both for cracks and for flatness/warp. The block should also be checked for flatness. Only a machine shop can do the flattening required if it's necessary. If you pull the head, you might as well also spend the money to have the valvetrain serviced by a machine shop. That will restore worn valve seats, seals, etc, and keep your van tip top for much longer.

A pressure test on teh cooling system will usually diagnose a bad head gasket or cracked head. A good place to start.

J

You guys are good. Its as if you were riding in the van with me. It is slow to heat up at first. and at idle it will get so hot, you can actually see the guage rising. if im crusin at 45 to 50 the temp will go down a little. I havent been on the highway in a long time, so i dont know if crusin at 80 will make it overheat. (im too scared the engine will blow up on me ) also i tested the thermostat by boiling a pot of water and i put the thermostat in, and it opened up just fine. the oil looked fine to me. i dont remember what the antifreeze looked like when i replaced it, cause i just drained it on my driveway . now it still looks clear. i replaced itabout two weeks ago.

how could the gasket blow or the head crack. Is it just faulty parts, or it was strained. Ive never done a burnout or anything like that before, so i dont think it was strained.


Thanx 4 all da quick responses

Hey Mike...

The head gasket seals all the little coolant and lube passages between the head and the engine block. Also, of course, seals the combustion chambers. It's a large gasket sealing 2 large mating surfaces. Often the heads and block are made from different metals (typically aluminum heads on iron blocks). The metals expand differently when they're heated. They are heated every time the engine starts. That differential expansion causes one surface to become bigger faster than the other, so there's always a force trying to cause the parts to slide against one another. Eventually, the gasket is weakened by this repeated attempt to shift the parts, and it fails. You don't have to abuse an engine to require a head gasket replacement.

A head cracks the same basic way, from thermal expansion stresses. Usually, a head doesn't crack until some other problem has caused an overheat. It's pretty common for a head gasket or a thermostat problem, or any other cooling system problem to result in a cracked head if the operator continues to drive the vehicle once it's overheated. Usually the cracked head is a symptom of an earlier problem. Sometimes, tho, a head will just crack. Maybe a deep puddle splashed water on a hot head, and the resulting fast cooling causes the crack to form. Or perhaps a casting weakness, manufacturing flaw. Impossible to prove, of course.

Some engines thru time have been famous for eating head gaskets. The old neon engines, for instance, and the older still K-car 4 cylinders.... And many others. Sealing that mating surface is one of the biggest engineering feats in a modern engine....

J

Thanx 4 the info. yesterday (thurs.) i took out the thermostat and left it out. It was way better. i was able to drive longer, but it went about three quarters of the guage, about 230 degrees even without the thermostat . i guess ill just take a week to take off the heads and replace them. thats going to be h$@L to take off. theres pretty much no space in that darned van to do stuff like this. the engine is completely under the van. the only way to get to is is from the inside of the van. it took me about 3 hours just to replace the spark plugs. oh well. If replacing te heads and gaskets dont work, i might just trade it in and get a new van.

Also is there any home remedies or tricks to find out if there is a crack in the heads. Id just like to know before i go tearin the thing apart . i saw on the discovery channel that they have this red dye you put on the metal, but i dont know if they sell any thing like this.


Thanx 4 all of the quick responses

Make sure your fan is on right when you replaced the clutch fan.
Make sure its sucking air not pushing it.
I have seen people put them on backwards.
And take the rad to a shop and have it check.
flushing it dont get everything out .
Before you spend money on doing the heads have the other things done.
And make sure the rad cap is good. Woody

Replaced the AC system? With what, did you get put in there? I put R134 in my car that had R12 orginally and adapted it somewhat and it blows cold air. But one of the things I was warned about was engine overheating with the AC on as I needed a larger rad and other stuff to convert over, but as it is, mine ran fine, but a little hot.....
Other things I think of, restricted exhaust flow, (cat conv) or pipe, yes, a bad thermostat or its in backwards, or bad head gasket. A bad water pump too might do that, a crimped hose or restricted hosd will do that, gradual warm up, heat up, and then way off the chart. Blistered plugs, yes they are running hot, either wrong plugs, or again some other engine trouble. Timing retaded or advanced too far??
Ever get it on an code reader to see whats going on?
After all this I would spend the buck to see what it says.
The most simple things cause the nasty problems and we go off track looking for the worst.
Restricted hose, hmmm disconnect one and see what flow you get.

eddie

Hi. The fan can only be put in one way. None of the hoses are bad, and i am running the van without a thermostat, and its still over heating. let me repeat that NO THERMOSTAT . Wierd huh???? It is a 95. did they even make r12 in 95? Any way, it is r134a, and i did put r134a coolant in it. it has a new pump. timing is also good. it has the correct plugs.

Today i started on the heads. I had to take off both manifolds (fuel injection), the upper manifold had lots of carbon in the ports. The lower manifold was just as bad.

Also the oil around the push rods was all gooey. The oil had gunked up around the push rods. It was as thick as bearing grease. It was clogging up the oil holes that lead to the heads.

Now my van has about 155k miles on it. When it had 98k miles (just under the 100k miles limit warenty) the engine got all messed up it was smoking badly, and it was loosing a lot of power. I took it in and they said it needed a new engine. it cost about $2000, but i got a refurbished engine. So the engine has only about 57k miles. i wonder if those d$#n GMC mechanics messed up my engine. This wouldn't be the first time this has happened to me. I had a 1992 hyndai (cant spell it sorry ) and they were just supposed to cange the computer. When i get home i found some blots missing. One from the egr valve. And they had messed with the timing, because as i drove it it was backfiring. When i got home i checked the timing and it was way off. They didnt even need to open the dang hood, why would those idiots even open it. Ill never take it to a repair shop agian. It makes you wonder what the mechanics are doin to your car when you take it in.

Any way what could have caused the gunked up oil. (besides sabbotage )

running with no thermostat is bad. all that does is heat up all of the coolant and does not give any a chance to cool. overheating is inevitable when there is no thermostat.
as for oil gunking up, my only experience with this problem was due to the oil losing viscosity and turning to sludge. in my case, it was due to just not changing the oil. very expensive lesson let me tell ya. as for them sabatoging, can't really see it but then again if you take it there for oil changes, I might suspect they are not doing it.