Water Temperature Again?

[marts1]

I thought i had the problem sorted.....but heres the situation...

1. Sitting on the drive..start it up..temp goes up to spot on 90 after a while it moves inbetween the red and the 90 mark and the fan comes on...takes the temp back to spot on 90..so not a problem

2. On the move driving normally, the temp now sits at just above 90 and sort of moves between 90 and half way between the red all of the journey but the fan does not cut in and the car does not over heat

Do you recon i have a dodgy gague or something?
I have flushed the water and double/triple checked that there are no air bubbles etc. The thermostat works ok and the rad flows water perfectly!

Any ideas

[19560]

Sounds spot on. The temp is rising to just under where the fans kick in and then a flow of air brings the temp down. I say go and enjoy the car.

[keithyboy]

Sounds similar to how my S1 used to run when I had it. Have you considered replacing the water temp sensor, this is more likely to be faulty than the gauge itself?

>> Edited by keithyboy on Saturday 8th November 10:53

[GreenV8S]

Basic behaviour sounds about right, so I'd check the gauge accuracy first by measuring the actual coolant temperature via a separate thermometer.

[bills1]

Always check the the pressure cap is well in place.
They are only just long eniough to provide a seal and often you think you hsve put it back ok and the seal is not quite perfect and the temp then goes high.

One way of helping this is to add a rubber washer at the bottom of the pressure cap(cut out of inner tube will do. It will help the seal.
The best is to get a longer reach pressure cap which is what I did. This will guarantee your rad is running at pressure.
Since fitting this to my S1 I have no trouble and only rarely need the fan.
The engine runs at a steady 90 even in long queues this hot summer.

Also the pressure cap needs to be on the swirl tank although you are most likely sick of us all telling you this.

Bill

Before this it often went over 90 which caused me to keep checking by removing the cap. Sometimes it was ok and these were the occasions when I unwittingly put the cap in 'good and tight'.

[bills1]

By the way Keithyboy how is the V8S comparing to the S1.
More grunt for more cost but how is like to live with.

[GreenV8S]

bills1 said:

Also the pressure cap needs to be on the swirl tank although you are most likely sick of us all telling you this.

This has been debated at length in the past. There do seem to be two distinct schools of thought, with people firmly for and against both arrangements. I've tried both ways round with no particular problems, although others have reported problems with one or other arrangement. I suspect it depends how well the caps fit as much as anything else. Also there do seem to be at least two header tank arrangements, and there may be others. So what is right for one car may not be right for another.

The layout that seems most common has a small pipe from the top of the metal swirl tank to the bottom of the plastic header tank, the header tank also has an overflow from the top that is conected to fresh air.

This works OK with a pressure tank on the swirl tank, as long as you have a pressure cap that fits properly. (The neck is too tall for a standard pressure cap to seal properly.) Advantage of this arrangement is that there is no stagnant volume so the system pressurises relatively quickly. The header tank is simply used as an overflow tank so that water blown out when the system is hot can be sucked back in again when it cools down. This only works if the pressure cap and connecting pipe are all air tight though, otherwise any water that is blown out will be left in the overflow tank. As long as all the seals are good, this is a good safe arrangement.

However, I believe the system was designed to work with the pressure cap on the header tank, and it does (in my experience) work better this way round. The reason it works better is that the pressure variations as you rev the engine push water back and forth between the two tanks, swapping the aerated water /froth from the top of the swirl tank with degassed water that has settled at the bottom of the header tank. This is very effective at extracting air bubbles from the system and collecting them in the header tank, where they will eventually seep out past the pressure cap.

My conclusion is that it is very important you have one pressure cap and one blanking cap, and that both caps and all pipes seal properly. It is less important which way round you put the caps, but my advice is put the blanking cap on the swirl tank and the pressure cap on the header tank. And whichever way round you have them, remember to BLEED THE RADIATOR every few months. If you let air build up in here, all bets are off.

>> Edited by GreenV8S on Saturday 8th November 21:00

[marts1]

Thanks for your help....again

Last night i found out what my mystery surprise from my mrs was......A three day trip to Wales to drive my TVR around the mountains etc

I guess this will tell me if the cars going to be reliable or not

[keithyboy]

bills1 said:

By the way Keithyboy how is the V8S comparing to the S1. More grunt for more cost but how is like to live with.

You really can't compare them IMHO. I always wanted the V8 but couldn't afford it at the time. The S1 was a good example with excellent paintwork and a good front end after I completely rebuilt it! The handling was excellent as a consequence although the poor ground clearance always hacked me off big time. After a while I was hankering after more grunt though and was seriously researching having the block bored out to 3.2L. This would've required all the other work that goes with it e.g. uprated brakes etc etc. However, an unexpected windfall allowed me to chop the S1 in for the V8S. The best move I've made. I only wish I could've afforded one initially as there really is no comparison! Try one and you'll see what I mean