+1 on air stuck in the system. Note that 'pressure bleeding' and bleeding per the repair manual are not the same thing.

Try the 'Cooling System Flushing' procedure, and maybe have a shop do the 'Vacuum Filling' procedure.

Is the waterpump original? I don't think you mentioned changing it.

Was any cooling service done prior to this issue? This just started out of nowhere?

 

Good advice from the lads, me i would get it checked out ASAP at local garage if you are unsure

 

You need to define high pressure. Your cap is prolly 14 psi? To force flush with higher pressure you'd want to disconnect the inlet and outlet hoses from the radiator and even then know that cooling systems aren't built to take high pressure. If your radiator is clogged and you want to flush it, you'll want to disconnect it anyway because you don't want to let loose whatever's clogged into the rest of the system.
Personally, I don't think you're done diagnosing. I still recommend putting an infrared thermometer on the hoses, inlet and outlet of the water pump, thermostat. A failing water pump can mirror your symptoms. So can a partially open thermostat.

 

The waterpump is new.
So you would think it is because of air in the system?

This issue was there prior changing all these things. Maybe it was the reason why the engine got faulty

We changed the engine and all the parts like waterpump, thermostat and cooling fan.

 

ah, now we're getting somewhere. Yes I would flush the radiator and backflush it while disconnected from the rest of the cooling system.

 

Yes , easy enough to back flush with the garden hose. A ladies stocking over the outlet would capture any debris that might be in there.
In the OP’s original post, said he changed the auxiliary water pump. Is that the same as the one in the block?
I’m thinking air in the system. Was the heat fully on when bleeding?

 

I am a „she“ but ... we also changed the auxiliary sater pump because it was cheap and easy to replace.

Yes heat was on.

 

Sorry. Didn’t catch that in the posts.
This is a tough one as you have fixed most of the obvious stuff. More obscure things like fan turning the wrong way or incorrect hose connections may be worth double checking.

 

Does the heater get hot? If not, that would point to air in the system.

 

Yes the heater gets hot and if the heater is on the highest setting it cools down the cooling water temperature.

If I set back 22 degrees for ventilation then the cooling temperature increases again

 

@Chibbi , I performed a test on a car's cooling system in the craziest of fashions, when I was a teenager playing with cars:

Everyone is going to laugh, but here it goes.

I over bored and over 'carburated' my entry level mid engine car, an X1/9.
(I had the aim to be able to squawk the tires at every gear change and beat all my friends with thier novas, mustangs and camaros on a very windy road)

And it was always overheating... to get to the root of the issue, I wanted to confirm flow... I bled the system at every bleed screw point and then bypassed the radiator (in the front of that car) and cooled the engine by circulating through in a big metal bucket.
(crazy teenage kid on a budget solution)
But I did learn, the radiator was not doing the job and I needed to increase the flow by increasing the diameter of the cooling pipes (yes, pipes on that car) and getting a larger radiator.

 

Thanks for the tip. I can bypass the radiator to check whether the temperature gets cooled by an external cooler.

If yes then the radiator must be faulty

 

That is good .....then coolant is at the heater and the heater is acting like the radiator should.
Check the radiator more

 

Put an aftermarket oil cooler in line with rad in my TR6. Could sit in traffic all day no overheating.
BTW I'm not laughing...very creative.

 

This is a highly informative thread and am learning lots about X150 cooling system

 

When I fill mine I open the 17mm socket cap on top of the aftercoolers and fill the expansion tank. Once both levels are the same I'll burp the system by squeezing any hose I can find and the air comes out of the 17mm cap. It take a while to burp them but once done I can squeeze the hoses and feel the coolant flowing.

 

Hi Chibbi,
are you sure that it’s the correct thermostat. All the XK parts suppliers in the UK list a 3/4 part stat.
It sounds like a restricted flow at low water pump revs. The multi part stat has various by-passes etc at various water temps.

I changed the stat on mine last year and ordered one on line which was listed for my car but when arrived it was a one part model.
It didn’t look right to me so I returned it and went to the main dealer and got the correct one which was multi part.

 

100 degrees Celsius at idle on a hot day isn't unusual or harmful. 118 degrees is. In your first post you said it was getting up to 118. If the changes you have made so far have lowered the temp to 100 at idle, I think you've fixed your problem.

I have the 5 liter engine, and it regularly gets up to 105 Celsius when I'm idling in the drive-thru lane.

 

Hi Chibbi
have gotten anywhere on solving the overheating?

 

Not yet ... I have to look for somethibg which can cool down the cooling fluid to test whether the cooler is faulty or not.

A new one will cost about 900€ here in Germany :-(

Does anyone have a used one in good consition maybe?