A while back (September) I got my K3, it over-heated from day one and two weeks into ownership I took the head off with the intention of replacing the gasket. That was the last time it moved.

When the head was off the level of corrosion to the block and head indicated that a new gasket was unlikely to ever seal in this engine again. I bought a replacement engine which was immaculate internally, replaced the head gasket, water pump, cam belt etc. Ever since I've been putting it all back together with new bushes, bearings, ball joints and so on, bearing in mind I'm working in the road outside my house this has taken some time.

The entire cooling system has been replaced, including new temp sensor and fan sensor, it has an MGF radiator and all the hoses have been replaced with silicone at some cost. I've also fitted a PRRT system using a new thermostat, the old thermostat has been modified to suit with the valve section removed.

Today I finally had all the pipes on, after spending a not inconsiderable time chasing drips and leaks the car was started up. It warmed up gently before the needle headed towards the red before dropping quite dramatically and then rising again over the next 5-10 minutes, the fans don't cut in and running them in manual over ride makes no difference, the radiator does get hot.

I have bleed points at the radiator, heater top hose and the metal pipe that runs to the water pump. The expansion tank and cap are new. The car is on axle stands at present, slightly nose down as I live on a hill.

The car shouldn't be over heating so I've obviously missed something. All suggestions are welcome....

Air lock somewhere ?

But front radiator and rear engine doesn't make good water flow on idle.
Where is the fan sensor placed ?

The Drop sounds like the thermostat opening, then enough cool water enters and it closes again.
Try upping the revs a little and see what happens.

Worth looking at http://www.mgfcar.de/thermostat/Water_System_Mods.htm
as MGF is similar setup.

Hi Ken,

The fan sensor is the standard K series unit bolted into the outlet on the head, I'm hoping it is an air lock as I'd hoped the remote bypass thermostat would prevent the up and down temperature see-saw and the subsequent stress on the head gasket.

Hi Rich

Can't remember exactly what other steps we took when I had My K3, but I know we ended up with the back end of the car jacked up as high as we could, before we got a loud burb (from the car) and the last air lock cleared

Thanks Malcolm, did you have similar symptoms prior to the airlock clearing?

Mine's an A series in a Rossa but for what it's worth I jack the back end up as high as I can and fill it slowly through the thermostat housing. So far I've never had an air lock......

Sorry Rich, I forget it was a fair while back.

No worries, family issues hit today's work on the car so it'll be after the night shifts before I get another go at the ruddy thing.