temperature sender explanation

[Bob696]

I have had an on going over heating problem (well the temp gauge reads high) which has got worse since I started messing.

Everything seems to check out. Radiator is clean, changed the temperature sender unit, changed the header tank, changed the thermostat.

Heres the interesting thing I found today whilst comparing the new thermostat with the old one. The 'old' one was from a 2.5N/A engine (82 degrees) and the new one is 88 degrees?

So several questions

1) Does the temperature sender unit in the engine send an electrical signal to the gauge on the dash which the gauge then displays? If this is the case could it be possable that the gauge is calibrated wrongly e.g. it is from a 2.5 N/A defender and it is mismatched with the sender unit so the only way to get the correct reading was to fit a thermostat from a 2.5N/A and therefor 'fool' the gauge.
OR
Does the temp sender unit send a preset signal to the gauge when it is at the correct temp and it wont really matter which gauge is fiitted?


2) What are the implications of running a 200Tdi 6 degrees cooler than it should be.

I hope all of the above makes some sort of sense  :shock:

[drmike]

I think you may well have mismatched sender and guage. I can't see that it's got anything to do with the thermostat which just opens and closes at set tempretaures and everything to do with how the guage inerprets the information from the sender. But no doubt someone more knowledgeable will be along shortly.
Mike

[Bob696]

well I was thinking the thermostat may come into it if it is keeping the water cooler than it should be and therefor leading to a false reading ... its all very confusing :oops:

[drmike]

Hold on Bob I didn't buy a set of springs off you did I?

Personally when my own LR showed it was running very hot I opened the bonnet and smelt the engine. In my experience a truly hot engine smells of hot oil and also makes that nasty ting noise as very hot parts cool down.

I had an air lock which was causing the water around the sender to get too hot and hence make it look like the engine was overheating. That said I went home on the back of an AA truck and fixed it rather than risk boiling up!

Mike

[Bob696]

Hold on Bob I didn't buy a set of springs off you did I?

I think so ... well somebody did  :lol:

The engine isnt getting that hot ...its just damned annoying and I dont like the idea of not having accurate information. If it gets really hot at the moment how will I know except when the engine goes BANG  :oops:

p.s. Hope the springs suited

[drmike]

Yes I bought the springs and they did the job beautifully - transformed the handling off road and we did very well at the next trial.

I agree about the guages being accurate. I can't stand it when things don't read right. Anyway I bet you need to fit the sender unit to match the guage. I think they are all the same size but I'm not sure. I had the same problem with a V8.

Mike

[Xtremeteam]

as u prob no ive just fitted a disco tdi into my 90 which was a n/a diesel before,know the temp guage sits at the bottom of the red when at normal temp & when the fan kicks in at 92 or 95 its at the top of the red,

cant put a defender sender in as the thread is different so was thinking of fitting a tim's temp guage that would read the actual temp of the water or retp the threads but cnt b bothered with the hassle  :lol:

[drmike]

Of course you can't get the Disco gauge to fit the Defender which I hadn't thought of.

A friend had a similar problem and fitted a resistor in line to get the needle in the right place. He got the engine nicely warm and as I recall used one of those remote thermometer things to measure the temperature of the block to make sure the engine was running at the right temerature and then tried various resistors until he got one that worked getting the needle in mid range.

I was never totally convinced that this was a good plan but it worked for ages.

Mike

[hobbit]

The other way is to fit a mechanical unit rather than electrical, did thid on mine when the rad was not cooling properly, its more accurate, and wont fail if the electrics pack up, just that sometimes you have to search around for the right converter to fit it to your threads