Mechanics

CHEVY OVERHEATING ONLY WHEN DRIVING

1999 Chevrolet Malibu

Engine Cooling problem
1999 Chevy Malibu 6 cyl Front Wheel Drive Automatic 146000 miles

Hello, this is my moms car, and recently she started having overheating issues. The antifreeze had been disappearing for a couple months, and there were no leaks anywhere below the car. We decided to replace the lower intake gaskets, hoping that was where the antifreeze was going. Now, the antifreeze is always full, so one problem solved. However, now we have another. We replaced the thermostat for her as well, and I think I may have gotten a bad one, or one for a different temperature. Ever since replacing, she has had practically no heat. And the car is still overheating. I can idle the car in the drive way for as long as I want, and it will not overheat. The fans kick on, and the temperature holds steady. I can drive the car for about a mile or a little over and it overheats. It's like clockwork. If I take the same route whenever I test drive it, it overheats at the same street everytime. The coolant is forced out of the reservoir, so I have to refill it. If I turn around, and head towards her house, its downhill most of the way, so I can coast a lot, and it wont overheat as quickly. And I have noticed that when it starts to get hot, if I let off the gas and coast, the temperature will come back down after a minute. And everytime the temp comes down, I will have hot heat for a few minutes. As soon as the temp starts to get hotter, the heat gets colder. I was wondering if a thermostat could cause all of this, or if it might be something else entirely. I replaced the lower radiator hose because it was brittle on the backside and I know they can be sucked shut by the water pump when they are soft. I also replaced the serpentine belt because it was worn. Any suggestions would be greatly appreciated.
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Khaan
January 7, 2009.




It can be as simple as replacing your coolant reservoir cap. If and only if it is not maintaining the 15psi the cooling system requires.

If that doesn't work, you need to have the vehicle pressure-tested leak down tested to see where the coolant is leaking too.

Check your oil. Is it " milky"? If it is, along with your description, you have a tell tale sign of bad head gasket.

Tiny
Zackman
Jan 11, 2009.
There is a Technical Service Bulletin for your situation.

ENGINE RUNNING HOT/OVERHEATING & /OR LOSS OF COOLANT
TECHNICAL SERVICE BULLETIN
Reference Number(s): 00-06-02-001, Date of Issue: January, 2000
Related Ref Number(s): 00-06-02-001
ARTICLE BEGINNING
ENGINE RUNNING HOT, OVERHEATING AND/OR LOSS OF
COOLANT (POLISH RADIATOR FILLER NECK AND REPLACE
RADIATOR CAP)
Model(s): 1999-2000 GM Passenger Cars and Trucks with Composite Radiator End Tank
Section: 06 - Engine/Propulsion System
Bulletin No: 00-06-02-001
Date: January, 2000
CONDITION
Some customers may comment on one or more of the following conditions:  Engine running hot
 Engine overheating, and/or
 Loss of coolant/low coolant message

CAUSE
The radiator filler neck may have an imperfection in the sealing surface.

CORRECTION

NOTE: Do not replace the radiator.

Using a piece of 400 grit wet/dry sandpaper backed with a flat piece of wood, polish the filler neck
sealing surface using a circular motion.
Replace the radiator pressure cap with a cap of the same part number as shown in the GM Service
Parts Catalog.

Tiny
Zackman
Jan 12, 2009.
[quote] Sorry Zack, but one other quick question that I think is obvious, but want to double check. The problem they are talking about is on the reservoir correct? [Quote]

It is. You don't have a filler neck on the reservoir itself. Your only access is through the coolant cap. Whatthey are saying is that the cap can't seal tight due to the imperfection around the filler neck. Let me know.

Zack
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Tiny
Zackman
Jan 13, 2009.

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