Overheating!

[Brad1234]

Hi all,

Sorry if this topic has been covered before but ive recently got a series 2, 4.2L 2+2 and it is overheating bad, within 10 minutes the coolant leaks out of the expansion tank. The radiator all seems to be working as it all gets hot. I am going to change the thermostat and fan switch but the 2 electric fans aren’t coming on until the temperature gauge is just touching the red zone, is that normal? And anyone suggest what else to look at or what to do haha?

Thanks!

[cactusman]

Sounds like the fan switch may be dud. When was the coolant last changed....might be worth flushing through with water to see if there is sediment in the radiator.....others will have other suggestions too. Hope you get it fixed as the fans should come on before you are in the red section.

[abowie]

Basically cooling function involves

1. Successful delivery of heated coolant to the radiator
2. Efficient dispersal of that coolant through the radiator
3. Adequate airflow across the radiator to remove enough heat to maintain coolant temperature at an optimum level.

Factors affecting:

1. Water pump, adequate coolant level and type, water ways in hoses, block and head not blocked or corroded. Thermostat functioning.
2. Radiator tubes not blocked and good flow through all parts of the radiator
3. Fan function adequate in terms of CFM flow and thermostatic fan control working. Radiator fins not damaged or blocked with dead bees, preventing adequate air flow from accessing heated air in functioning radiator.

I would do the following.

1. Bypass the thermostatic switch on your fan so it runs all the time. Start the car and leave at idle for your 10 mins. If it overheats then you may not be getting adequate airflow. Confirm by driving the car. If it overheats at idle at rest but is OK driving at speed it suggests this too. Fix fan and remove bees.

2. If it does not overheat, then remove the bypass on the thermo switch and see if it now overheats. If it does, replace the switch and see if this solves the problem.

3. If it does overheat after replacing the thermostatic switch, then 1 or 2 are likely causes of your problem.

Then, in order of increasing difficulty:

Replace water pump belt and check tension is correct.
Remove the thermostat and do not replace it. Run the car. If it does not overheat put in a new thermostat.
Run a cooling system flush chemical through, and get the block professionally reverse flushed.
Remove and replace all coolant.
Have the radiator checked and repaired/recored/replaced as appropriate.
Replace all hoses.
Replace the water pump.

If that doesn't fix it you're probably in strife.
.

[Brad1234]

Thanks for the info, going to try all this at weekend!
Water pump has just been replaced but not sure about the rest. Ordered a few parts and will fit them at weekend. The radiator has had leak stop in i noticed yesterday so that could be blocking areas but both inlet and outlet pipes are getting warm so quite sure water flow is flowing ok.

[mgcjag]

Hi....to check the thermostat start the car from cold...put one hand on the engine and the other on the top hose...as the engine gets to the temperature that the thermostat opens you should feel the rush of hot water through the top hose as the stat opens........if it dosnt then the stats not operating correctly....that is assuming the water pump is working..Steve

[abowie]

but both inlet and outlet pipes are getting warm so quite sure water flow is flowing ok.

That tells you that some water is getting through but not how much. Radiator places use an air flowmeter to assess flow and resistance to flow.

Let us know how you get on.

[abowie]

Found this too; not sure where it came from. You could check your temperature gauge sender too..

"Later temp sensors were different construction being
thermistors and worked a lot better. They had the following
curve.

-10c 9200 ohms
0 5900
+20 2500
+40 1180
+60 600
+80 325
"

[PeterCrespin]

Hi all,
....within 10 minutes the coolant leaks out of the expansion tank. The radiator all seems to be working as it all gets hot. anyone suggest what else to look at or what to do haha?

Before you get too deep...

Define ‘overheating’.

Coolant expands, so puking out of the tank could easily be - and often is - due to overfilling.

It doesn’t help that one of the handbooks tells owners to fill to the neck. I am sceptical your car is overheating and would not touch anything without more info. All your effort could easily be wasted, as the coolant will still expand and puke no matter what you do if you are overfilling. In which case, stop adding coolant and lesve it alone to find its level each time it experiences a new highest temp.

If you’re certain you aren’t overfilling and have blank cap correctly fitted and the sprung cap the correct length then you can dig deeper.

[abowie]

Define ‘overheating’.

He's right, you know.

[Brad1234]

The temp gauge goes to the red zone is that not over heating? Steams aswell

[Brad1234]

Thanks for the ideas though, ill check the level but im sure it wasn’t filled right to the top

[mgcjag]

Hi...check that you have the correct caps fitted.....plain on the rad with no spring....7lb on the expansion tank

[MSM]

The temp gauge goes to the red zone is that not over heating? Steams aswell

But you have also said that the fans do not come on, if they did it is unlikely that the temp gauge would go into the red zone.

[Brad1234]

Yea very good point thanks! Im gonna try with the fans first then.