Another symptom on VW Caddy heater not getting warm

'08 Caddy 1.9TDi van. I notice that there is some heat inside the cab. if I rev the engine over about 2000 rpm. Below that, the cabin heater
output is just cool. Measured the engine coolant temp and its 78 deg C - so on the cool side.
Sounds like water pump would you say? thx
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If it was the water pump the engine would be overheating. Thermostat seems much more likely. Air locks and a sludged heater matrix are also possible but if the coolant temp is low then your thermostat is the prime suspect.
Tim
Tim
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wrote:

Oops - I should have said, - have changed the thermostat.
Yes I wondered why the engine temp is on the low side too. Can't really explain it but am certain it is the case. Steady Rev the engine for a few second and warm air comes out the heater. Back to idle, back to cold air.
I put the van up on racks, open the heater to full open and ran engine for 10 mins - still the same situation.
Looks like a sludged-up heater matrix then - which is a damn awful thing to get at in this VW.
When I changed the 'stat, the coolant that came out looked very clean!
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On 11/03/2016 20:55, mike wrote:

I would look for an airlock first. you could find if the heater is sludged up by running a domestic hose pipe to it and seeing how easily the water flows through if it runs through at a dribble it is blocked, otherwise it is OK
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