300tdi engine in a 2.5td Chassis- Overheating

Evening All

This is probably the easiest problem to solve, or the complete bugger...

I put a 300tdi engine in my old 2.5td chassis. It is all done and someone even MOT'd it!!!

Since then though, the temperature gauge is constantly on the red (and tonight coming home from work it was even above the top of the red!!) even though the coolant level is fine, as is the oil.

I have taken a few steps to check things, and I have worked out that the pump is working (I removed the brass screw from the top of the pump and the water gushed out), but the water is not reaching the heater matrix (I removed each pipe from it and nowt came out from either). I even removed the some of the pipes from the front of the engine and there was no coolant movement there either.

I have asked a few friends and they all say conflicting things, but one that answer that has cropped up is the thermostat is knackered, and therefore for opening when the water gets hot.

If this is the reason, how would I check the thermostat for correct operation, and is it an easy job to change it...??

Or can there be another reason for this overheating problem...?

Cheers in advance for any help given!!

remove it and dump it in a pot of boiling water to test

the sensor and the gauge have to be from the same vehicle.

change the sender to a 2.5td one.

is the engine red hot? or is it just the gauge? if just gauge sender or gauge it self.

mhm quicker on the keyboard again

thought it was mine! said:

is the engine red hot? or is it just the gauge? if just gauge sender or gauge it self.

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The engine is hot, but not mental so (warm would be a better word...). I am a chef so I am used to heat (asbestos fingers...) but I can easily keep my hand on the top of the engine, and the rad is not too hot either.

The Mad Hat Man said:

the sensor and the gauge have to be from the same vehicle.

change the sender to a 2.5td one.

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So as it is the gauge from a 2.5td and the sender from the 300tdi, it could be that it isn't overheating as such, but would this stop the water circulating? My journey to work is 18 miles each way, and at no point do I get warm air out of the heater vents, and half way to work today when the gauge was above the red I stopped and checked the water movement, and there was none...

Am rather confused now...

Dalai Farmer said:

So as it is the gauge from a 2.5td and the sender from the 300tdi, it could be that it isn't overheating as such, but would this stop the water circulating? My journey to work is 18 miles each way, and at no point do I get warm air out of the heater vents, and half way to work today when the gauge was above the red I stopped and checked the water movement, and there was none...

Am rather confused now...

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No it wont stop it, thermostat does


However my 300 doesn't heat up in this weather at all, get to about 1/3rd to 1/2 way when doing 70 on a long journey but other than that it sits at c, even if doing 55 its only just up to the base of the line

18 miles isn't much really especially if stop start with the viscous going

Dr_evil said:

No it wont stop it, thermostat does


However my 300 doesn't heat up in this weather at all, get to about 1/3rd to 1/2 way when doing 70 on a long journey but other than that it sits at c, even if doing 55 its only just up to the base of the line

18 miles isn't much really especially if stop start with the viscous going

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I have removed the viscous fan and fitted an electric one. And the gauge gets to 'red hot' within 1 mile, even in this weather...

calm down think simple engine not red hot gauge say's it is so gauge or sender problem. not thermostat or engine out to check. Don't dive in try simple first

Take the thermostat out and see if that cures the circulation problem. That's is the real problem, as others have said you probably have a mis smatch with the gauge and sender.

The Mad Hat Man said:

the sensor and the gauge have to be from the same vehicle.

change the sender to a 2.5td one.

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I still have the old engine in my garage, so I will change them over. Will it be a straight swap over or does it require an adapter to make it fit properly?

And where can I find the sender units on each engine???

i did the same conversion on my 90, the sender for the 300 sends the wrong signal to the 2.5 td gauge, so always in the red, however the 2.5 sender does not fit the 300.

i got a new gauge reading in temp deg 40 - 120 of ebay and a sender to match. now in running about 75 - 80 deg all the time which is better to know than red or blue.

cheers Gary

dv8i said:

i did the same conversion on my 90, the sender for the 300 sends the wrong signal to the 2.5 td gauge, so always in the red, however the 2.5 sender does not fit the 300.

i got a new gauge reading in temp deg 40 - 120 of ebay and a sender to match. now in running about 75 - 80 deg all the time which is better to know than red or blue.

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I did conversion of my 2.5TD to a 300tdi and had same problem with gauge and sender. You must use a 300tdi gauge with the 300tdi sender.