At a loss....

The Godfrog · Jul 3, 2018

Folks,
I have an ongoing saga with my cooling (or not) system in a D90 300Tdi. My thermometer starting reading high and nearly going into the red after a few miles. To cut a long story short I have now: replaced the thermostat, the sender unit, the top and bottom pipes and the water pump. I took the radiator out and thoroughly examined it (it looks in good nick) and I flushed and back flushed it. I refitted it, refilled and then drained and refilled again very carefully in case I had an air pocket. Now it doesn't get more that 0.5 mile before going into the red! I have tested the thermostat in a tin and it opens at the right temp.

I'm now very frustrated so any advice on what to do next would be welcome.

Disco1BFG · Jul 3, 2018

I suspect you're having gauge issues, rather than anything else given what you have done .... Temp gauges on 300 series deafeners have something of a reputation

.

So, how hot is the engine really .... ( you need to know this ...)

how solid is the top hose when the engine is "hot" ...

what happens if you leave the ignition is position two for a white - say ten mins - does the gauge move then ? - or try putting the battery on charge whilst the ignition is on - ( see if the increased voltage send the gauge loopy )

If you leave the expansion tank cap off - can you see evidence of the water pump actually pumping - they can fail - impeller comes off the shaft and no water circulation = overheating quite quickly

Can you get access to a proper IR thermometer, or fit a proper capiliary gauge? (Durite are very good IMHO)

A search on here should give a few other things to check ....

Kwakerman · Jul 3, 2018

Dont trust a LR temp gauge especially after doing an engine swap. Gauges may all look similar but their characteristics are different and designed to match a particular sender type. Best bet is to get a decent matching gauge and sender set, numbers are better than just blue/red scale. I vent for VDO and that showed I had a stuck open thermostat while the original gauge was still reading mid band.

The Godfrog · Jul 4, 2018

Disco1BFG said:
I suspect you're having gauge issues, rather than anything else given what you have done .... Temp gauges on 300 series deafeners have something of a reputation .

So, how hot is the engine really .... ( you need to know this ...)

how solid is the top hose when the engine is "hot" ...

what happens if you leave the ignition is position two for a white - say ten mins - does the gauge move then ? - or try putting the battery on charge whilst the ignition is on - ( see if the increased voltage send the gauge loopy )

If you leave the expansion tank cap off - can you see evidence of the water pump actually pumping - they can fail - impeller comes off the shaft and no water circulation = overheating quite quickly

Can you get access to a proper IR thermometer, or fit a proper capiliary gauge? (Durite are very good IMHO)

A search on here should give a few other things to check ....

Thanks - very helpful. I'll start looking at those items. I have brought an IR thermometer so will get to work with that first. A capillary gauge sounds interesting..... are these easy to fit?

The Godfrog · Jul 4, 2018

Kwakerman said:
Dont trust a LR temp gauge especially after doing an engine swap. Gauges may all look similar but their characteristics are different and designed to match a particular sender type. Best bet is to get a decent matching gauge and sender set, numbers are better than just blue/red scale. I vent for VDO and that showed I had a stuck open thermostat while the original gauge was still read mid band.

Thanks I'll have a gander.

zeaphod · Jul 4, 2018

If the engine is running at normal temp (80-90 degrees) you will be able to hold your hand on the rad top hose- just. Once the engine gets to 100 and over you will smell the hot oil and the top hose will be too hot to hold. I highly recommend fitting a Durite (other gauges are available) gauge and sender - you'll then know exactly what the temp is.

Disco1BFG · Jul 4, 2018

The Godfrog said:
A capillary gauge sounds interesting..... are these easy to fit?

Yep, for the most part ... worst bit is getting the capilliary gauge tube through the bulkhead without damaging it, or something else...

- "its" sender will just screw into where the current sender is now - you might need an adaptor ... and of course your old gauge will be useless without its sender - but given its, er, accuracy .... I doubt its much of a loss

At a loss....

The Godfrog

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Disco1BFG

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Kwakerman

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The Godfrog

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The Godfrog

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zeaphod

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Disco1BFG

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