Tech advice for a 75e17

Hi all,
Need a bit of advice please.
I used my Cargo to move a lot a gear over to my French gaff recently and came out of a service station to find the brakes wouldn’t release due to poor air build up.
Ive just replaced the blown compressor head gasket (its a 53 plate Tector 75e17 by the way) which has got me moving again but since then the water temp is erratic, sometimes not registering at all, sometimes shooting to 100 in a couple of mins till I release the rad header cap.
The compressor head was water cooled so Im guessing I just have an air lock in the system somewhere but everything ive tried has failed to sort it over the past week.
Is there a special sequence to bleed the system?
Cheers in advance

Don’t rule out it having been a problem with the cooling system that caused the compressor to go by overheating.
Have you checked the coolant pressure?

Own Account Driver:
Don’t rule out it having been a problem with the cooling system that caused the compressor to go by overheating.
Have you checked the coolant pressure?

Cheers

Checked the pressure and found that the system isn’t holding any.
Header cap checked and working ok and then found a small rusted through hole in a steel pipe.
Ive managed to temporarily cover it with a rubber hose and the system now holds pressure so going to see if it makes any difference tomorrow.

Remove header tank cap and dump the air by pressing the brake pedal a few times. As the compressor fires in watch for air bubbles from the header tank. If bubbles appear when the compressor is under load you have a cracked compressor head.