My 16 year old son's 2000 V8 Chevy pickup has been running hotter than usual after he went to add coolant to the reservoir and it was still under pressure. It dumped alot of coolant out. He has since refilled it but now it's running about 235 degrees and it starts to overheat when he runs the AC.

Today he let me know that he's been adding water every day prior to driving his truck to make sure it's full. He told me that when he drives for awhile and he stops and turns the engine off, it dumps coolant out of the over pressure line of the reservoir.

If he doesn't have enough coolant(antifreeze) to water ratio will that cause engine to run hotter than normal? Should we just go ahead flush the system, and replace the thermostat? Why does the engine overheat whenever running the air conditioner?

Please send me some suggestions before I start on this project. Thanks in advance.

 

Well when you keep adding water to an antifreeze water mix you dilute it, and yes water has a lower boiling point than a 50/50 mix of antifreeze and water.............first thing I would do is pressure test the cooling system (you can rent the tool from most parts stores) then if it tests good I would flush the system and change the thermostat......but there is more to the equation than just that....the fan, and the water pump are still in question also....when you pull the thermostat put it in a pot of water with a meat thermometer and see what the temp is when it opens......should be around 195...........when you run the A/C you create additional heat (needed to create cool air....I know its weird but true) there is alot to it but that is the just of it.........when the truck is warmed up have you pulled the cap to see if there is circulation in the radiator? ( caution this is a no pressure system when running but caution is still needed)

 

He's right on. Also not alot of people know this but the given t-stat temp is the closing temp, not the opening temp. So a 195 t-stat will usually open at about 205, then it will close at 195, hence temperature regulated at 195. So if your gonna do the t-stat, might as well do a flush also but after you figure out the spewing problem, which it probably is a bad t-stat. Parts stores sell 50/50 mix anitfreeze off the shelf so that will save time.

 

Chris, this model truck does not have a cap on the radiator, only on the reservoir tank. The overpressure line I am talking about is on the reservoir.

Last time we added water to the system, we left the cap loose on the reservoir. As the truck warmed up to operating temp, we added more water until it was full. We put the cap back on but it was a little tighter than before. As we went to add more water it spewed over from the cap. If this is a non pressure system should it have spewed from the reservoir fill cap?

 

Ruff, I've read where people are using regular antifreeze as opposed to dex-cool mixture. The 50/50 mixture you are talking about is it regular antifreeze or should we stick to GMs recommendation on coolant?

 

Well the motor in that truck is iron not aluminum so the green stuff will do fine, that is what I use on my 2001. And they have 50/50 in either regular anti-freeze or dex-cool.

 

You can still pressure test the system..........they make an adaptor for it............I have this nagging in the back of my head that says it could be a blown head gasket..........thats why I suggested the pressure test

 

x 2 bad head gasket. The big question no one is asking is: Is the truck still under warranty? If so take it to the Steelership... Other wise I am thinking bad headgasket like my buddy's truck had. Did everything you described.

 

weak fan clutch is a possibility as well... testing gets a bit dangerous though lol

 

I was afraid someone was going to say blown head gasket. I guess my first day off, Thursday, I will run a pressure test. I will keep you guys posted and thanks for the help.