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Jason, ASE Certified Technician
Category: Chevy
Satisfied Customers: 28
Experience:  6 years experience, Associates degree in automotive technology
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2001 Chevy Malibu came in with a running hot problem. Replaced

Customer Question

2001 Chevy Malibu came in with a running hot problem. Replaced bottom and top radiator hose, water pump and reservoir tank with new pressure cap due to threads being stripped on tank. Since then I haven't been able to get the heat to work again. one hose going into the heater core is hot and the other is cool. All lines and heater core has been flushed out and are clean. I'm not getting any pressure to the heater core at all. I've never had a problem with air pockets on a 3100 engine like this before. what do you think?
Submitted: 7 years ago.
Category: Chevy
Expert:  Jason replied 7 years ago.
I've had a couple that were very stubborn before. One thing that usually works is jacking up the front of the car to raise the radiator to the highest place in the cooling system. The air should all go into the radiator and then out through the air bleed hose. If that doesn't work, then try a vacuum cooling system refiller. I've got a Matco one, I'm not trying to push this particular brand, I'm sure they all work just the same. The P/N for mine is MCR101, which can be found here. It pulls a vacuum on the cooling system which completely removes all air, then you open a valve and the vacuum in the cooling system pulls in coolant to fill it.
Customer: replied 7 years ago.

I've already tried jacking up the front end till the rear bumper was almost hitting the ground and I also have the Matco Vacuum tool and have tried that also. I haven't tried pulling a vacuum on it since the hoses was replaced though. Do you normally just pull a little vacuum say about 15"hg and then open the valve for the coolant until the gauge reads zero and then repeat?

Expert:  Jason replied 7 years ago.
I let it pull a complete vacuum then let it suck the coolant in, then remove the pressure adapter and run the engine until the thermostat opens then pull a complete vacuum on it again (of course the repeat is only for a problem like this).

If it doesn't overheat running it in the shop, put the pressure cap on and take it for a hard drive. The high RPM coupled with bumps in the road will help dislodge air pockets. I had a car that I tried everything else on and then a co-worker suggested this, it worked great.
Customer: replied 7 years ago.

Thanks Jason,

I'll try this either today or Monday first thing and let you know how it goes. Wish me luck and I'll come back and accept your answer.

Thanks again!

Expert:  Jason replied 7 years ago.
I was just reported for failing to mention that this engine has a special coolant fill procedure. This procedure involves running the engine at idle with the air bleed screws opened to allow air to escape from the cooling system. There is an air bleed screw on the top of the black metal pipe right above the water pump. Some systems have a second air bleed screw on the thermostat housing, others have a hose that runs from there to the coolant reservoir. Systems that have the hose only require that the air bleed above the water pump be opened, which I believe is true of this particular vehicle.. Be sure to keep the coolant full while doing this. Once the thermostat opens, close the screws.

From what you said, I understood that you are an automotive technician and you suggested that you have bled the cooling system on the 3100s before. I apologize if I was wrong about these assumptions. If I was wrong about this, then the first thing you should do is the coolant fill procedure that I explained above. If you have any questions about this, please let me know.
Customer: replied 7 years ago.


You were right with your assumption I am a technician. With this engine I have always just opened the bleed screw that you mentioned and filled the system with coolant until it ran out of the bleed screw then replaced the screw, tightened, and started the engine and brought it up to operating temp. Then I would open the bleed screw until I got a steady stream of coolant coming out and re-tighten. In the past by doing this I never had a problem.

Sunday I went to the shop and pressure tested the coolant system again with the engine cold. The shop was quite and as soon as I put pressure to it I could here a leak. I found that the intake gasket was leaking.

Monday we replaced the intake gasket. Went through the fill procedure and had the very same results (No heat at idle). I placed a large funnel in the surge tank and filled it up. I then ran it through several temp. expansion cycles watching the air bubble out. After doing this I had heat with the engine at idle. I drove the car and after about a mile I lost heat again. The air temp. would fall off until it was cool and then all of a sudden come back and be extremely hot and then get normal heat again. It did this several times before me getting back to the shop.

I plan on running it through more cycles of the same today (Tuesday) and seeing if that will help? This thing has been a demon and defied all logical troubleshooting! If you have anymore suggestions please don't hesitate to let me know. The customer has been very patient so far but I'm not sure how much longer that can last. I'll let you know how today goes.

Thanks again for your input so far.


Expert:  Jason replied 7 years ago.
Did you try the vacuum bleeder again after replacing the lower intake manifold gasket? You probably weren't getting a complete vacuum before with the gasket leaking.

Two other things that usually make the bleeding easier are: 1) take you 'type a' adapter for your spill free coolant funnel over to the bench grinder and take off the lip past the rubber seal. This will let you put that on the thread on adapter for the surge tank, filling the funnel to the top will increase the pressure on the system slightly, and sometimes helps to push air pockets out. 2) install the pressure cap and let the system get up to operating temp. Then slowly open the bleeder until you get some coolant, then close it. Keep repeating this until the pressure is gone from the system. It may also help to rev the engine until you get the hot-cold cycles from the vents, there may be some air left that's causing it.

The hot-cold could also indicate a blown head gasket pumping air/exhaust into the coolant.
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Customer: replied 7 years ago.


I went in this morning and when we started the engine up the first thing we saw was coolant gushing out of the surge tank indicating a blown head gasket. we pulled the heads and now have them sent out to the machine shop for re-surfacing. For what ever reason this thing never really indicated a blown head gasket until now. The leak was obviously very small and got larger all of a sudden.

Expert:  Jason replied 7 years ago.
I'm glad we got this figured out, even if the fix isn't something easy. Thanks for choosing, and thank you very much for the bonus.

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