Hi Everyone:

Just joined, will send general greeting later, however, really need a few hints as whether anyone out there has experienced similar problems. I purchased a 2002 Silhouette with 129K on it, 2 years ago. Have about 180K on it now. Has run pretty well all along, however, whenever the weather changes with the temps going down and the humidity is up, I start to have an overheating problem. The problem will continue during the cool fall, the cold of winter and the cool of spring and then completely subside during the summer.
The van will overheat, especially quickly if I am idling for more than 1/2 a minute or so. Temp. gauge shoots steadily up till it'* almost max. and then temp. warning will display. At that point, I usually pull over, shut it down for 5-10 minutes and then restart and continue on my way. Sometimes the overheat problem returns right away and sometimes everything is ok until the next time a couple of weeks later. This problem occurs with in-city driving or highway driving.
Strange thing is, that when this occurs, the heater does not blow hot air. However, if after a little while the heater does kick in properly, the temp. gauge quickly returns to normal.
Now, have had fluid checked each time and fluid levels are OK. Have had fluid tested each time and fluid checks out within acceptable levels. Have had thermostat replaced, thinking that was the problem, and problem was not alleviated. Have had cooling system flushed and fluid replaced, pressure tested, no leaks and many more checks, ad infinitim.
Has been scoped at the dealer and it shows no irregularity. They don't seem to have any sense of what it could be, perhaps even electrical??????????
But funny as it seems, to me, an old guy, it is acting eerily similar to a "vapour lock", which used to happen on cars that I owned back in the 60'* and 70'*, but should not be possible now.
Anyways, van is equipped with a 3.4 litre.
If anybody has any ideas or has suffered from similar problems, your insight would be great.

Thanks

seems like maybe something with your water pump, have you done the serp. belt?

Sounds like an air lock in the system. Is there a bleeder on the 3.4?

I think you are looking at one of the following:

1. air in system
2. fan relay
3. engine coolant temperature sensor

First thought is air in the system. Look for a bleeder valve on or near the thermostat housing. Crack it open with the engine at operating temperature and running. Place a cloth over it so you don't burn yourself.

Next thought is low or high speed fans not coming on, or coming on at the wrong temperatures. There are wax crayons that melt at different temperatures you can use, or purchase a non-contact thermometer (http://www.ebay.com/itm/Non-Contact-IR-Laser-Infrared-Digital-Thermometer-NEW-/260864898771?pt=LH_DefaultDomain_0&hash=item3cbcc2 76d3) so you can monitor coolant temperature, and from a cold start watch for the fans to kick in as the engine warms up. If one of the fans is not kicking in, it is probably a bad relay. If they are not kicking in at the correct temperatures, it could be an engine coolant temperature sensor.

Water pump has a little residue on it, so perhaps it should be changed. However, it overheated again this morning and I let it cool down enough to get to a GM dealer. Just got off the phone with them and they said, it is the heads, they need machining and a new gasket. Cost between $2500 and $3000. Did not pay that much for the van; so anybody know of a used 3.4 litre engine available or another used van with 100K or so on it.

Anyways, greatly appreciate your input.

Definetely not air lock, have had it bled and flushed a few times. However, it overheated again this morning and I let it cool down enough to get to a GM dealer. Just got off the phone with them and they said, it is the heads, they need machining and a new gasket. Cost between $2500 and $3000. Did not pay that much for the van; so anybody know of a used 3.4 litre engine available or another used van with 100K or so on it.

Anyways, greatly appreciate your input.

I am going to check out everything that you have told me, when I get a second opinion on this, later in the week. BECAUSE ------ It overheated again this morning and I let it cool down enough to get to a GM dealer. Just got off the phone with them and they said, it is the heads, they need machining and a new gasket. Cost between $2500 and $3000. Did not pay that much for the van; so anybody know of a used 3.4 litre engine available or another used van with 100K or so on it.

Anyways, greatly appreciate your input.

Get it out of the dealership and if you have another ride or can get one, visit your local parts stores. They all have cash customers that work out of their homes and will know the good ones. They may be leery at first but if you buy the head set and related parts needed they will probably open up and suggest a good tech. That job should only cost around $600 to $700 parts and labor. Overheated 3.1'* and 3.4'* are known for this problem. Why it happens in the cooler times as opposed to summer has me baffled.

Actually, my next door neighbour fixes cars in his driveway all of the time, and having known him for 15 years, I am pretty sure that he will take cash. Don't know if he has done a head gasket before, but I have seen just about every other type of job done there. By my research, the 3.4 L had a lot of gasket problems from 1999 to 2004. Then in 2004, GM had so many repairs and replacements, extended warantee'* etc., that they eventually dropped the engine and replaced it with a 3.5. However, I am not sure if it was mainly the head gaskets or the lower manifold gaskets that they were having problems with, as I have seen a lot of both. I will certainly follow-up on your recommendations; however, I have one more question for you if possible. The research that I did said that there is little point in replacing the head gasket unless you do 3 other things: 1) machine the heads flat - as there will be normally .003" to .006" of warpage 2) determine what caused the gasket to leak and fix that problem before you replace the gasket. The research said that you can determine the cause my examining the gasket for burn or compression. 3) Check the heads for cracks

If you concur, please reply.

Thanks for all of your valuable input and advice. It is very appreciated.

you cant know for sure until you pull the heads and check with a strait edge and feeler gauge. if your neighbor does work on cars have him check out the heads and gaskets. the dealers are replacement artists, they just dream up the jobs that will net them the most money. 3.4'* had the issues with the gaskets till 03 i think, my late 03 monte with a 3400 didnt have any issues. i think they had a revised design.