Hello All,

My first post, although I use this forum a lot, but never needed to post before - always found the answer via other threads.
Anyhow, my heater is blowing cold and the temp gauge hits the red when I travel over 60 mph - this just happend recently durung the cold snap (2 weeks ago), but as soon as i slow down it drops to about the 3/4 mark.
I had a leak in the radiator, so I've actually put in a new radiator and new coolant, but still have the same problem.
1. I'm thinking it may be an air lock. I've located 2 bleed screws, 1 on the top of the radiator and 1 on the supply pipe to the heater matrix and they both seem air free - is there another bleed valve I may have missed on the engine block? If so where can I find it?
2. If it's not the above, then how much work is it to replace the thermostat (and how?)
Not even thinking of engine problems yet

It's a 2004 Doblo Cargo 1248 cc multijet diesel.

Cheers, Paul.

Sounds like the coolant isn't circulating around the system, or there is a blockage somewhere. You have bled the air from the radiator and the highest point which is the bleed on pipe to the heater matrix.
So if there is still no heater it would seem that the water pump isn't circulating the water or something is blocked up.
If the system froze up it may have damaged the impeller on the water pump. Even with a stuck closed thermostat the heater would work and produce a lot of heat! A stuck open thermostat would make the temperature gauge hardly lift off the stop and poor heat output.

Thanks murphyv310,

I disconnected the heater matrix supply and return and blew through the matrix - all is clear. In fact I can blow right through the full system via both the supply and return lines of the heater matrix.

Would this suggest the thermostat is stuck open?
Never thought about the water pump.

Is it easy to replace the thermostat and/or water pumps. Looks like not much room - battery out etc I guess.

Cheers, Paul.

Same thing happened to me with the overheating and cold heaters ended up it was the water pump.
had water pump and timing belt and kit done for £250 at a local garage works fine now

Hey thanks sidewalksurfer,

Unfortunately that's not what I want to hear - just removed the thermostat (pig of a job) and it kinda looks pretty good (not that I would really know but it's moving freely on the spring). New thermostat coming tomorrow (90 quid here in Holland ) - at least I'll have a spare
I'll get it all back together tomorrow, and I just know it'll be the water pump - let's see.
Ah well - maybe it's time the timing chain was changed anyhow.

Thanks for the advice

Paul.

It does really sound like the water pump. You will get a certain amount of cooling at low speeds due to thermo syphon..
I really doesn't sound like a thermostat fault.