Sudden Temp Guage Drop

[Catkins]

So having had to try to refill the coolant in my K series R300 due to a hose popping off and having carried this out using the strong waggling of the lower hose attached to the radiator method I seem to have now developed a hairline crack at the point where the stubby aluminium tube that the lower pipe connects onto attaches to the radiator. I have tried to seal this with a hardening metal putty to no effect so resigned myself to getting this professionally re-welded (if that is possible?). Needing to drive the car to Caterham for a service and probably to get this sorted there I decided to see how my refilling efforts had worked and so started the engine up to bring it to temperature. All seemed well and it seemed to rise to just over 80 and stayed there for a while (I was only letting it idle and a little bit of movement up and down the small road outside my house as no MOT) I was about to turn it off when suddenly I next looked at the temp gauge this had dropped to zero but the fan had just kicked in so seemed to be still hot. Help Please!! Is it safe to drive!? Could an air lock cause this?

[Rich N]

If the temp gauge drops to zero I would suspect the temperature sender.. take the spade connector off and touch it to a grounded metal place in the car.. it should go full scale if the gague and wiring is fine.

[Catkins]

thank you Rich N.....would you be able to give me a numpty description of how to locate and identify this?

[Graham King]

The temp sender is in the water rail, just above the exhaust headers. It will have a single wire connected to it, touch this on the engine block.

 

Graham.

[Catkins]

Thank you very much Graham. Apologies but just to double check I am just going to touch the disconnected wire on the engine block to see if that makes the gauge move and that is whilst the engine is running to confirm that the wiring is working fine which means the temp sender is faulty or do I take out the sender and wiring?

[MADMALC]

No need to have engine running just ignition in the on position. Just detach the wire/spade from the sender and earth same to the engine block. Make sure the bit you earth to is clean bare metal, ie no paint.

Full deflection is good gauge likely faulty sender.

[Catkins]

Thank you very much madmalc for the reply . I took the clip off and cleaned it a little then re-attached it and started the engine again and the temperature gauge seemed to work this time (or it climbed to around 85 and seemed to stay there with fan cutting in). Could it have been a bad connection or is there the possibility of anything more sinister or am I just paranoid!?

[grumpy the 7th]

Catkins, hi (right time of year for you to come out 😬)

 

The sender is sh!te and very tempremental. If you gently twist the spade connector either way you will probably find the plastic insert thingy will twist within the brass housing. After swapping mine twice I twisted the last one till it stopped and I've not had a problem since. (sods law says it'll now pqack up )

 

Anybody know of a more robust alternative sender??

[Catkins]

Hello Roger ...I do like it when the weather starts to change! (hopefully more time in the car when frustrating issues don't interfere!!) 😬

Thanks very much for the re-assurance.