View Full Version : Help with my overheating Geo please

03-01-2004, 05:01 PM
I have a Geo Prizm that likes to get real hot at freeway speeds but not so hot at around town speeds.

I don't know the exact temps but when on the freeway, my water temp gauge is just below the red line and around town is 1 1/2 marks above half.

The manager of Advance Auto parts said it was probably a cracked head gasket letting hot air leak from the exhaust to the intake or I had a crack between valves.

It also spits out a puff of white smoke out of the exhaust at start up but doesn't really smell like oil but it does stink pretty bad.

Also, I notice when I disconnect the PCV valve hose from the intake it starts idling real fast. Is this normal? Can a faulty PCV valve cause overheating?

I have 140,000 miles on the engine. What else do you need to know?

03-01-2004, 07:12 PM
When a motor gets hot at higher speeds but runs cooler at stop and go, it usually means insufficient radiator capacity. In other words, you have a clogged radiator. If it's old, just replace it. Simply pulling the PCV out of the grommet, should not affect idle at all. If you pull the hose off the valve, that introduces a big vacuum leak. If the car is fuel injected, I would imagine the computer would richen up the mixture causing the engine to run faster.

03-01-2004, 07:26 PM
If ya look uder the hood there is a squirrel in a wire wheel -- he needs a drink:laugh:

Sorry couldn't help myself:spank:

1 bad gs
03-01-2004, 08:33 PM
mark, a bad pcv valve will not cause overheating. if you had a crack on your cylinder head your car would overheat driving around town also, not just at high speeds. first check a couple basic things. with the engine COLD open your radiator cap and make sure your coolant level is full. next step is make sure your radiator fan is turning on when the engine temperature starts to climb. the next two things, if the thermostat is older than 3 years put in a new one. ive seen many high mileage cars that have the front of the radiator covered with dirt, leaves, and also cottonwood. this would cause an overheat condition. ive also seen high mileage cars with the water pump impeller shaft rotted or busted off. again if your water pump is original replace it. hope this helped, good luck.

03-01-2004, 09:49 PM
damaged or restricted exhaust system could cause what your car is doing.


lower radiator hose could be collapsing after periods of higher rpm.


some aftermarket ground effects (front bumper) kits can flow the air around the car and not through the grill as needed AND add useless weight to the car all at the same time.:Dou:

03-01-2004, 10:10 PM
Aftermarket stuff on this thing? Now that's a good one! I appreciate all the comments. The radiator is the original one as well is the water pump. I changed the thermostat about four years ago. I think I'll start with the cheap stuff first and work my way up to the radiator.

It's interesting that you mentioned the fan coming on because it won't until it gets real hot like 3/4 of the way on the temp gauge. I flushed the radiator with radiator flush two weeks ago thinking maybe it would unplug the radiator if that was the problem.

Also, I'm developing an exhaust leak somewhere in my down pipe off the manifold.

1 bad gs
03-01-2004, 10:21 PM
couple things mark, an exhaust leak wont cause an overheat. i would do a thermostat, and pull the radiator out . 140k is asking for trouble with the original radiator. if its looks like its dirty in front you can clean it with compressed air. if it looks like the fins are clogged inside replace it.

03-01-2004, 10:26 PM
change your thermostat. it may be stuck half open causing sufficient flow at idle but not at higher speeds. as for the puff of white smoke in the morning its probably due to the milage on the vehicle. i dont know about a geo but on a honda or toyota if you disconect the PCV it will idle rough or sometimes idle higher. i would change the thermostat first though. be sure your fans are kicking on also.

03-01-2004, 11:34 PM
to help enforce what i said before ....

the exhaust leak very well could be a sign that your exhaust/converter/muffler or pipe is clogged/smashed. the exhaust pipe is held to the manifold by spring pressure that is the weakest point.
GO TO A REPUTABLE EXHAUST SHOP AND HAVE THEM CHECK IT OUT. tell them what is goin on. it will only take them about 10 minutes and they may not even charge much if anything for it for the diagnosis.

03-02-2004, 07:28 AM
Picking up a thermostat tonight.

FYI: The Geo is a cross breed between a Chebby Nova and a Toyota Corrolla.

The exhaust looks good as far as not being smashed. I put a new muffler on it last year. The cat. converter could be clogged. I'll have it checked.