As a breed, if past threads are anything to go by, we seem beset by over-heating and running temperatures generally in our cars. I am no exception.

Assuming an 88 degree thermostat would you consider 90 C be a normal operating temperature?

Would you expect the running temperature to fluctuate at normal speeds on the road ie above 40mph between fan on at 95 and faling to just under 90C?

Does the thermostat just open or close or does it constantly vary its opening in an effort to maintain a constant running temperature.

Probably if I had a gauge marked Cold Normal and Hot instead of being calibrated in degrees and no lamp indicating fan on I'd probably not worry.

Any thoughts greatly appreciated. Thank you in advance.

Sorry posted under wrong heading

[Edited on 10/12/09 by 2cv]

A thermostat opens according to temp, so there is a few degrees between just cracking open and fully open.
Can you just get a cooler stat?
Darren

Also how well is the gauge calibrated?Thermsistors are very varible even for the same batch.

[Edited on 10/12/09 by turbodisplay]

I've got an 85deg stat and I get 88 to 96 degrees running temperatures. The 96 degrees is 'fast'motorway driving in warmer weather which means extended periods at 4000rpm+.

My fan switches on at 104 degrees and takes about 30 seconds (when stationary) to bring the temp downs to 99 degrees where it switches off.

Never had an overheating problem or used any coolant.

Ed.

I had a water rail and the temp was up and down, cold, dead hot.. put the original thermostat housing back on plumbed it up as it was in the donor and its solid now. Warms up quickly and sticks at 86 degree's.

IE: OEM plumbing is the answer.

Thank you for your replies. Just to give you a bit more information, engine is in the back(mid-engine) where the temperature sensor is located and the radiator is at the front of the car with a screwed in thermo-switch which operates the fan automatically. At something over 90 but much less than 110C the fan cuts in. It switches off at just under 90C indicated by the gauge. The thing that surprises me is that under seemingly steady state conditions, the temperature does fluctuate around the 90 mark, sometimes causing the fan to come on. I'm just surprised about this and wondered if others have seen the same thing. So far, it hasn't boiled nor lost any coolant.

Hi, have you checked that there is no air locked in the system. It might be an idea to bleed the system, with the temperature fluctuating as you say.

quote: Hi, have you checked that there is no air locked in the system. It might be an idea to bleed the system, with the temperature fluctuating as you say.

Good point. I have an air bleed valve set at the highest point on the system and there is no air at this point. However, and this might be critical, the small tube at the top of the rad which would normally go to the header tank I have blanked off but only after having filled the system with coolant with this port open until fluid comes out. The heater works fine and flow and return pipes are hot.

So, should I run a bleed pipe back from the rad to the header tank? I only haven't done it because it's a pain being such a long run of small bore pipe.

Where is the radiator located,
even if front mounted, could the airflow be insufficient?
Darren

On a properly set up cooling system the temperature should remain rock steady during cruise conditions.


It looks to me as if your system doesn't have enough by-pass flow giving the effect that when the thermostat opens a great slug of over cold coolant is deposited into the bottom of the engine.

It might be advisable to ditch the conventional go to a modern setup with the thermostat in the bottom hose and much greater by-pass flow.

If you do a Google search on the "PRRT Thermostat"(sometimes called PRT) tthat was used in the last MGTFs and has been retro fitted to a number MG-Rovers, Freelanders and Lotuses with great success.
The PRRT thermostat gives much better control and more even spread of coolant temperature throughout the engine avoiding hot and cold spots. Bought on its own it is a fairly cheap Landrover part for the TD5 the part number is PEM100990 or MG-Rover PEL100990
see ebay item

links http://k80rum.co.uk/cooling.aspx

http://wiki.seloc.org/a/Fit_a_PRRT

[Edited on 10/12/09 by britishtrident]

British Trident says:On a properly set up cooling system the temperature should remain rock steady during cruise conditions. It looks to me as if your system doesn't have enough by-pass flow giving the effect that when the thermostat opens a great slug of over cold coolant is deposited into the bottom of the engine. It might be advisable to ditch the conventional go to a modern setup with the thermostat in the bottom hose and much greater by-pass flow. If you do a Google search on the "PRRT Thermostat"(sometimes called PRT) tthat was used in the last MGTFs and has been retro fitted to a number MG-Rovers, Freelanders and Lotuses with great success. The PRRT thermostat gives much better control and more even spread of coolant temperature throughout the engine avoiding hot and cold spots. Bought on its own it is a fairly cheap Landrover part for the TD5 the part number is PEM100990 or MG-Rover PEL100990 see ebay item

Thank you for your carefully considered answer and you could well be right. The symptoms do seem to fit. I shall certainly follow this up via the links you have kindly given. Thank you once again.

Nice work BritishTrident!