Technical overheating on idle

[marcelo100cl]

Hi All,

New to the forum, I have a 1997 barchetta (since new) and it developed an overheasting problem, and we have almost fixed it, but it still overheats when its on idle.

We have changed radiator, thermostat, cooling hoses, and bypassed the cockpit heating for troubleshooting purposes.
Now the car runs good and is able to maintain temperature and control it with the electric fans.

Only problem is when I stop with the engine running for 3 - 5 minutes (as in a traffic jam), it starts heating very fast, we have tracked the reason also, there is almost no flow of coolant at Idle, only a couple of lonely drops. If the RPMs are higher there is a reasonable flow, and the car manages to stay cool even in the hot summer we have right now in Chile.
We also checked the expansion tank and its not clogged, water flow well.

Has anyone experienced this? Do you think I need to replace water pump? (it was replaced about 12 years ago, so that could be something), but since the car only overheats in idle, and at normal running speed, even at sporty mountain backroads it is able to hold it's temperature.

Thanks a lot, sorry for the long post, Didn't find a similar issue in the forum.
Cheers,

Marcelo.

 

[wapper]

The water pump should be amongst the first things to be checked.
Probably it has plastic impeller that has deteriorated over time and is not able to push the coolant. On higher revs it works a bit better and the airflow through the radiator helps to cool down the engine.

 

[bugsymike]

It does sound like the water pump is the cause of your problem, not circulating water through the cooling radiator at low speed.
Normally I would have suggested the electric fan kit to start with, but you already have that, I assume it is coming on at that, point when engine at idle? If not temp probe that activates it may be situated in the wrong place if it is an after market kit.
Other than that a racing or heavy duty specialist radiator capable of dissipating the heat better may be the answer.
All this is assuming there is no underlying engine fault causing the problem?
I assume inspite of the high ambient temperature where you are that you do have the correct antifreeze in your cooling system.
It may sound stupid but it is also described as a "summer coolant", but more importantly it prevents corrosion between the different metals in the cars coolant system, which can block the core tubes inside the radiator , but also the inside of the engine block, I have seen engines stripped down that the lower part where supporting the cylinder bores in the castings have been heavily silted up meaning heat can not be dissipated.
Another point is you say you have bypassed the cockpit heating? If by that you mean a bypass hose so water doesn't circulate through heater radiator, this can actually aggravate the problem as manufacturers save money in radiator size by using the heater radiator as part of the cooling system permanently unlike the old days when a mechanical valve controlled heater operation.
Air con also puts load on a engines cooling system.

 

[s130]

A quick check for the water pump is the return hose to the expansion tank. On idle one should still have some flow of water back up to the header/expansion tank.

 

[marcelo100cl]

The water pump should be amongst the first things to be checked.
Probably it has plastic impeller that has deteriorated over time and is not able to push the coolant. On higher revs it works a bit better and the airflow through the radiator helps to cool down the engine.

Right, Yes that was my thinking too... but wanted to see if you guys saw other possible causes to check also. Thanks!

 

[marcelo100cl]

A quick check for the water pump is the return hose to the expansion tank. On idle one should still have some flow of water back up to the header/expansion tank.

Yep, we did that and at idle there's practically no flow.

 

[marcelo100cl]

It does sound like the water pump is the cause of your problem, not circulating water through the cooling radiator at low speed.
Normally I would have suggested the electric fan kit to start with, but you already have that, I assume it is coming on at that, point when engine at idle? If not temp probe that activates it may be situated in the wrong place if it is an after market kit.
Other than that a racing or heavy duty specialist radiator capable of dissipating the heat better may be the answer.
All this is assuming there is no underlying engine fault causing the problem?
I assume inspite of the high ambient temperature where you are that you do have the correct antifreeze in your cooling system.
It may sound stupid but it is also described as a "summer coolant", but more importantly it prevents corrosion between the different metals in the cars coolant system, which can block the core tubes inside the radiator , but also the inside of the engine block, I have seen engines stripped down that the lower part where supporting the cylinder bores in the castings have been heavily silted up meaning heat can not be dissipated.
Another point is you say you have bypassed the cockpit heating? If by that you mean a bypass hose so water doesn't circulate through heater radiator, this can actually aggravate the problem as manufacturers save money in radiator size by using the heater radiator as part of the cooling system permanently unlike the old days when a mechanical valve controlled heater operation.
Air con also puts load on a engines cooling system.

Thanks for the extensive reply! Yes, seems we have to check the water pump first.
I do believe we are using the right type of coolant, but will have to check to see if we have diminished flow on the engine (is there like a liters per minute flow rate of water that we should observe?). When we replaced the radiator we didn't see much deposits in the old one (nor the new radiator enhanced cooling very much).
And last, Good point about the heater radiator, I haven though it's helping the cooling system too (and we are not putting the air conditioning on..)

Marcelo.

 

[Foldsmobile]

Thanks for the extensive reply! Yes, seems we have to check the water pump first.
I do believe we are using the right type of coolant, but will have to check to see if we have diminished flow on the engine (is there like a liters per minute flow rate of water that we should observe?). When we replaced the radiator we didn't see much deposits in the old one (nor the new radiator enhanced cooling very much).
And last, Good point about the heater radiator, I haven though it's helping the cooling system too (and we are not putting the air conditioning on..)

Marcelo.

Just a thought - I hope you are replacing the cam belt regularly (3-5 years) - when a replacement water pump is normal for me.

DavidF