Very High Engine Temp in Traffic MK1

[Scotty65]

So can any of you MK1 brainiacs experienced/ solved this issue.
Its a 1471cc FD engine and has been cooling normally untill recently where suddenly in slow moving traffic its less than a hair below the red.
Changed the temp sender no change. Changed the head gasket (slight water leak before) no change. Flushed it, replaced the collant and still no change.
The water temp in the radiator appears still to be Ok as the fan operates as it always has and does not run constantly when the temp gauge is almost in the red.
Oil temp is unchanged and rearly exceeds 80 degrees
The temp sender is in the housing coming out the side of the head and goes to the the heater matrix and inlet manifold.
So it appears to be only the water coming out the head thats the problem?

Any random thoughts?
Cheers
David

[gldgti]

Yeah - check that you have good earth from the engine and the gearbox to the chassis. I had a bad earth once that was causing the temp gauge to go crazy (the sender wire was acting as an earthing point).

Rare engine too - nice one

[Peter Jones]

Voltage reg behind the dash could be an issue too. Is the fuel gauge also playing up?

[Scotty65]

will have alook at the earth lead to the gearbox make sure everything is ok but everything was good a tight last time.
Fuel gauge is working ok but I do have issues will low voltage when using lights and heater. Battery is getting the correct voltage 13.5v load to 14.4v no load but the volts drop to electrical equipment can get down to under 12v with lights and heater on but temp stays high either way.
I do have a new tacho unit so I could change it over to see if the problem persists

[Peter Jones]

Check the earth strap between the alternator and the engine.

Some motors have the alternator mounted on rubber bushes and should have a separate earth cable or all sorts of weirdness happens.

[IBN]

Check the earth strap between the alternator and the engine.

Some motors have the alternator mounted on rubber bushes and should have a separate earth cable or all sorts of weirdness happens.

Can second that. The straps get ratty with age. I had one fail and only noticed when I was poking around under the bonnet in the dark and saw the last few threads in the strap glowing red (!).

[twin eng, twin turbs]

The impeller in your water pump corrodes along with the housing over time causing coolant flow through the system to reduce. I have also had a sticking thermostat that didn't fully open causing overheating in slow traffic. For a simple test you can place your thermostat in a pot on the stove with a thermometer and see what temp it opens and if it opens fully, the temp it opens at is stamped on the thermostat.