Another overheating post :(

[MrHanky]

Hi,
 
Last week on the way to the final autotest of my local club, the coolant buzzer came on (despite the fact that I had just topped up), at this point I noticed the engine temp rising fast.  I pulled over and switched off ASAP.  Engine was very hot and coolant / water (ran out of coolant do had to top up with water) was bubbling away.
I waited for it to cool down and then limped home.
I noted at this point that my electric fan was not on.
 
Anyway I got the thermostat out yesterday and the first time I dropped it in boiling water, it did nothing.  I then emptied and tried again, this time it opened.
 
I also bridged the switch for the fan and it switched on.
 
This leads me to my questions:
 
Without the fan running (and assuming water is flowing around the system), is it possible for the coolant to overheat when moving at steady pace?
 
Would the coolant only reach high temps if it was flowing around the system in the first place?  I.e. will it get too hot just from residual heat, whilst sitting in its tank?
 
I felt the top and bottom pipes at the time and they were hot, which led me to believe that water was flowing, but im not sure if they too could get hot just from residual heat from the engine.
 
Any ideas people?  At this point im thinking its the sensor switch for the fan, but any other ideas would be appreciated.
 
Thanks
 
Mark

[Prof]

If you\'re moving along, then the rad should keep things in check, but obviously if you get stuck in traffic or hoon it a tad, then the temps will rise and the fan will be needed to assist cooling.
 
In addition, if the coolant isn\'t pressurizing, it will boil at a lower temp.  Also, if you\'ve an air bubble in the system that will affect cooling too.
 
As for residual heat - the engine can retain heat for quite some time, so when you shut it down, the coolant temp can go up a little before dropping.
 
Is your fan running directly from the thermo switch or via a relay (which is the right way to wire it)?  The switch on current for an electric fan is large and will create arcing on the switch contacts and cause premature failure of the switch.

[MrHanky]

Thanks for the reply Prof.
Forgive my ignorance but I am a complete numpty when it comes to most things mechanical and especially electrical.  Sensor wires for the fan feed into a small connection box which then goes to the fan IIRC, would this be the relay?  Will see if Brett knows if he sees this thread as it is his old car.
 
Just not sure what to do next.  Would it be to bleed system and try and make sure there are no air bubbles, then try again?
 
Thanks again.
 
Mark
 
 

If you\'re moving along, then the rad should keep things in check, but obviously if you get stuck in traffic or hoon it a tad, then the temps will rise and the fan will be needed to assist cooling.
 
In addition, if the coolant isn\'t pressurizing, it will boil at a lower temp. Also, if you\'ve an air bubble in the system that will affect cooling too.
 
As for residual heat - the engine can retain heat for quite some time, so when you shut it down, the coolant temp can go up a little before dropping.
 
Is your fan running directly from the thermo switch or via a relay (which is the right way to wire it)? The switch on current for an electric fan is large and will create arcing on the switch contacts and cause premature failure of the switch.

[Prof]

If it\'s Brett\'s and there\'s a small box - probably does have a realy - hopefully he\'ll spot this thread and confirm. :cheers

[Brett]

The fan sensor was a stock RS or CPC part, only cost a few pence so get another. The relay was in line with this and should on the wing next to the fuse box... Again, should be cheap to replace.

Probably worth investing in a new rad I would have thought, given the sprints etc?

[MrHanky]

The fan sensor was a stock RS or CPC part, only cost a few pence so get another. The relay was in line with this and should on the wing next to the fuse box... Again, should be cheap to replace.
 
Probably worth investing in a new rad I would have thought, given the sprints etc?

Thanks Brett.  Will get sensor, thermostat and relay changed just in case then.
Will have to see how much a radiator is, as funds are tight at the minute.
 
Thanks again all
 
Mark

[Brett]

No worries, drop me an email if you need to