water temperature issues

[jon haines]

So my car is slow to warm up according to the gauge, sticks at 70 for a couple of miles then creeps to 80 sticks for ages then in 5 seconds goes into the red and then back to 80 in the same time. Does not over heat or smell hot so could this be the sender unit? not an issue i have ever had.

[ElvisWedgeman]

It could be the sender or or could be the gauge. It could also be an earthing issue. Take the wire off the back of the sender with the ignition on and touch it momentarily on the engine block to make earth and watch the gauge. It should creep up all the way smoothly and fall back when not earthed. If this happens then it’s probably the sender. Fairly easy to change but may need calibrating the sender to the new gauge for accuracy.

PS. if both gauge and sender are good it could also be the thermostat???

Edited by ElvisWedgeman on Thursday 20th October 22:36

[KKson]

I agree with Tony. I would certainly put a new thermostat in as the first job, as the old one could be sticking. If that doesn't help then I'd suspect the sender unit. Make sure the swan neck is full via the blanking cap. If the sender is sat in an air pocket it could also give weird readings

[jon haines]

Cheers guys. Just had an engine refresh so will ask if thermostat was changed or not. I have a spare sender unit so will swap over.

[KKson]

The new stat should have a jiggle pin in it to bleed out any air. Be worth checking for air locks first. Cheers

[Pumpkin123]

I had similar symptoms when I had an airlock, did they change the water in the engine refresh...

[jon haines]

So coolant was changed but thermostat was not. Now I never had any issues before so could be an air lock.

[SLB]

Had a similar issue with mine when the radiator was repaired. Going into the red was a little worrying but it was all due to air locks and I ended-up letting it idle on an up-slope and then topping up the swan neck.

[Thundered]

Before changing anything electric - try bleeding the system first. Make sure the car heater is set to 'Hot'. From cold fill the swan neck to full then cap off Remove pressure cap from the header/expansion tank and fill to half way. Run the engine on a fast idle until the thermostat opens. You can tell as the water level in the header tank will drop slightly. Let the car idle and watch for the water to start 'burping' the air out of the system until it stops, the fans should also cut in to drop the temprature. Keep the car idling until the temp rises again, the fans should also cut in again once that happens cut the engine allow it cool with the cap off the expansion tank. When cool top up and replace the pressure cap and you should be good to go.

[adam quantrill]

KKson said:

The new stat should have a jiggle pin in it to bleed out any air. Be worth checking for air locks first. Cheers

Also jiggle pin should be at the top.

Instead of filling up at the swan neck blanking cap, I remove the small bleed pipe that goes to the swan neck from the expansion tank at the tank end, attach a small funnel, and top up while watching the expansion tank level. This helps getting air out.

The reason for not disturbing that blanking cap is that it's very easy to break the seal as it's not spring loaded.

But, I have lived with a similar initial warmup fluctuation issue for many years on the 350i and it never developed into anything worse, or lost fluid. It's just the way it works sometimes.