Caterham 7 no coolant temp

[Sumpplug]

I Have a 2005 Caterham R300 K series. After winter layup engine temp rose alarmingly. No sign of dreaded HGF, engine had a new water pump with cam belt around 600 miles ago.

I removed and tested thermostat in boiling water and it didn't open so replaced it. The old one was stamped 82 degrees so ordered the same from Elsie Parts.

Since refitting the thermostat and refilling cooling system the temp gauge refuses to budge further the about a millimetre off the cold end of the scale, even after several miles. The top house is warm to touch, bottom hose is cool.

I'm concerned the cooling system may be blocked and the engine is actually still overheating and we all know what happens to a K series if you cook it.

Has anyone experienced anything similar?

Thanks in advance

[Peter T]

Sounds like trapped air in the system. Does it have a heater? If so then bleed air from the top heater hose.

[Richard-D]

From that description it's just as likely to be a stuck open thermostat.

[E-bmw]

Both of the above should be the first obvious port of call from what you describe.

[DVandrews]

Check the gauge operation by removing the wire from the sender and breaching it to earth. If you know the gauge is OK, then check the spade connector on the water rail , these are known to come loose and give an intermittent reading.

If that is sound, warm the coolant rail area with a heat gun (carefully) to see if the gauge moves; if it does then no coolant is getting to the sender so a bleed / top up at the heater hose would be a good thing. If it doesnt then suspect the sender.

Oily

[stevieturbo]

get a cheap IR heat gun and see what sort of temps various parts around the engine are. Head, top/bottom hose etc. Presumably you can feel if water is moving through the system, heater etc ? as pipes heat up.

[jeremyc]

Bleed the cooling system with the nose of the car as high in the air as possible: the top hose/bleed screw on the radiator needs to be the highest point.

Run the car with the bleed screw open, header tank cap off and heater (if fitted) on full hot - hopefully that will get rid of any air locks.

[Sumpplug]

Thanks all for your replies, suspect it may be an airlock in the heater as many of you suggest. Will try re-bleeding it again, cheers

[Sumpplug]

You were all on the money, I jacked the front up and re-bled the cooling system with the header tank unbolted and raised as far as it would go. Seems to have cleared the airlock and the gauge is reading as normal. Appreciate all your help. Cheers