Wierd overheat problem

Hi Guys

I've had a search, but nobody seems to have the same problem as me (story of my life!)

A major HGF and overheat lead to a new head on my 300Tdi as the old one was like a banana.

Since then she keeps on airlocking. As you all know the coolant system is full of high points, so I unbolted the header tank and hitched it up

The advantage of being a boater is you can tie decent knots!

Brought up to operating temperature, heater working well, no apparent air in the system. No leaks either, with the system pressurised.

Replace the tank and take her for a drive, 20 miles or so and all's well.

Stop for a while, then drive on. System airlocked. No heater, expansion tank hot, no leaks. I've tried changing the cap to the expansion tank, but its made bugger all difference. No sign of HGF, and the mechanics swear there are no leaks on the coolant circuit.

She's done this several times and I'm at my wit's end. :frown:

Is there a micro leak, drawing air in as the engine cools???

Mike

Round black gizmo in pic with three pipes, name escapes me at moment- check not blocked

Stupid question but you have bled the syatem havent you. At the thernostat housing and the rad. Changed thermostat so it isnt sticking removed the ufo in the 3 way pipe to make sure its not buggered

And has your expansion bottle got a crack in it that leaks under running pressure.my tank had a split smack bang in the middle and was on the join.

fanatic said:

Round black gizmo in pic with three pipes, name escapes me at moment- check not blocked

Click to expand...

this is air bleed valve, part number PCH117840 - they are about £7, and best replaced on a vehicle of this age....

Thanks

I'll try the air bleed valve next. Expansion tank is newish.

Mike

Check under the front carpets around the transmission tunnel, the heater matrix is now +15 years old, they have a bad habit of leaking and letting air into and coolant out of the system.
Took me weeks to track the leak in mine, did the old noggin in until I saw the red coolant stain on the underside of the floor whilst checking out the gearbox oil level.

Problem resolved.

Mechanic put the heater return hose on to the bypass spigot on the water pump and the bypass on to the heater return. :wtf:

All's well that ends well. Just need to read up on changing the lock springs as three out of five doors are out of action...