Overheating....totally stumped.

David1206

Team Pro5 member
Contributor
:
2002 Protege5
So I'm having an overheating issue. It doesnt over heat at idle. But after a few minutes of driving, it gets hot. I flushed the radiator, put a new thermostat in it as well as a new water pump. The pump was installed about 2 years ago but not even 1000 miles have been put on it. I took then thermostat and drove it around for a whole minute but it finally overheated. The water pump is fairly new. Could it have gone out? I'm totally lost......
 

pcb

The Diagram Dude
:
2002 MP5
Make sure you don't have an air lock.

Turn your heater on full blast to flush out any bubbles.

 

pcb

The Diagram Dude
:
2002 MP5
It's a bubble of air trapped in the system that stops the coolant from flowing.
 

David1206

Team Pro5 member
Contributor
:
2002 Protege5
Ahhhhh......I guess I need to flush it again. What are the chances of that water pump being bad. It probably has about 1000 miles on it.
 

pcb

The Diagram Dude
:
2002 MP5
You shouldn't need to flush it again, you may just need to burp it.

I suppose your pump could be bad but they should last much longer than that.
 
:
2010 Mazda 5 Sport
A bad head gasket or crack in the block/head can cause a car to overheat fast like that. Check your oil for anything odd.
 

pcb

The Diagram Dude
:
2002 MP5
There's a tester you can get as a loan-a-tool that sniffs the radiator to see if there's exhaust gas getting into the cooling system. (bad head gasket or cracked block).

Overheating your engine can warp the head but you may get lucky and it was just a stuck thermostat initially and now it's just an air bubble.
 

David1206

Team Pro5 member
Contributor
:
2002 Protege5
I'll try that first. But the head was just rebuilt and I haven't let I get hot enough to warp the head. But there is nothing odd in the oil.
 
:
2010 Mazda 5 Sport
Your radiator fan is working correctly I assume?

If the burping doesn't fix it...I would suspect the head wasn't reinstalled properly and get the test kit to check for exhaust in the coolant like pcb said.
 

David1206

Team Pro5 member
Contributor
:
2002 Protege5
Nah. I drove it for a while after the head was fixed. The head isn't the problem. But the fans work as they should.
 

pcb

The Diagram Dude
:
2002 MP5
When I did a rad flush I left the rad cap off.
That way I could watch what was happening.
You can see when the thermostat opens when there is fluid movement.
Then the fluid level would drop and I would keep topping it up.
I would rev it up a bunch of times to help push the bubbles through and squeeze the rad hose to work the bubbles towards the filler neck.

If there are a few little bubbles left after you're done and replace the rad cap, they end up in the filler neck then get pushed out into the overflow bottle. Then when it cools, it pulls fluid back into the rad.
 
:
protege5
this is hands down the BEST way to fill a cooling system. No burping required, and you've completely filled the cooling system in a couple minutes as opposed to letting it idle with the heater on, etc while bubbles purge out for a half hour...

https://www.amazon.com/dp/B000IHK1VI/?tag=m20b7-20

I've use it for many years and can't imagine filling a cooling system without it. If there's a leak in the system, it will find it too. It basically pulls the entire cooling system into a vacuum. The hoses collapse, and there's no air left. Flip the valve with the hose in a jug of fresh coolant and it sucks the coolant right into the system. Done. Because it pulls the system into a vacuum, if there's a leak you'll see it losing vacuum when it's all pulled down, instead of holding steady on the gauge.


Otherwise, the only way to do it right is to get one of these https://www.amazon.com/dp/B01I40ZQWE/?tag=m20b7-20

it's a little cheaper, but you have to let the car idle for a half hour, revving it occasionally, with the heater turned on so coolant circulates through the heater core, etc. and just keep going until no more bubbles come out. can be a hassle, especially for some cars like a Toyota MR2 or Toyota Previa, where the engine is in the back of the car, or some Fords are a nightmare as well and CAN'T be done without an airlift...


check to make sure the radiator cap is in good condition as well. How is the coolant level, it is maintaining "full" or is it losing coolant? I've seen guys leave the radiator petcock a little loose as well, and it will drip out under pressure but not "leak" when you're sitting so you never know it's leaking anything. If it's maintaining the full level you may just have an air pocket where the coolant temp sensor is, so it reads a lot hotter than it really is...

lot of possibilities. but I agree first step I would do is drain the coolant and refill again, taking time and care to make sure there's no air pockets.
 
:
2001 Mazda Protege LX 2.0
So I'm having an overheating issue. It doesnt over heat at idle. But after a few minutes of driving, it gets hot. I flushed the radiator, put a new thermostat in it as well as a new water pump. The pump was installed about 2 years ago but not even 1000 miles have been put on it. I took then thermostat and drove it around for a whole minute but it finally overheated. The water pump is fairly new. Could it have gone out? I'm totally lost......
How old is the radiator cap? A bad one will make it overheat also. If you have air in the system itll cause overheating also,
 

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