Diesel help !

[john lang]

It's not a Merc, so I'm being a bit cheeky posting it here but....



> I've got a VW Passat 1993 with a 1.6 t/diesel engine. Since I changed the
> head gasket 25000 miles ago due to oil leaking from the gasket, it runs
> OK, albeit it seems to run a little hot with the gauge around the 95C
> mark. The heater works very hot so obviously the coolant is circulating
> around the heater circuit. It doesn't loose any coolant.
> However, in normal running, the thermostat doesn't seem to open and this
> bothers me a bit. The bottom of the radiator and bottom hose are cold
> (the thermostat is fitted in the water pump where the bottom hose fits
> onto the pump.)
> If I take off the header tank cap and let the car idle for long enough,
> eventually the thermostat opens and the rad/ bottom hose heats up. After
> a bit longer, the fan cuts in.
> I've fitted 2 new thermostats and they are definitely fitted correctly.
> Also a new sender unit for the temp gauge.
> So, is this normal ? Is it right that this engine is so efficient that it
> can stay cooled using just the heater and bypass circuit without needing
> the radiator except in a traffic jam ?
>
>
> Best wishes,
> John Lang
200E 16V + Passat diesel estate.

 

[NormanB]

Hi

Fault finding by remote is difficult but it sounds to me that your radiator is blocked.

At normal (or above) operating temps, the whole radiator should be hot - (of course there will be a temp gradient across) it but definitely no cold spots that would indicate there ain't no hot water flowing through that section.

Best case Radflush treatment and then off hoses and reverse flush. May be worth taking rad out and flushing off the vehicle. Some specialists shops may do a more aggressive citric acid based clean - you will have to ring around and check.

Worst case - new rad.

Good luck and keep us posted.

 

[john lang]

Thanks Norman, I should have said I've already had the radiator tested by a rad specialist and it's not blocked !
And when the car sits at idle and the thermostat does open, the rad gets nice and hot all over.
The problem ( or it might be normal) is that in normal driving the thermostat doesn't open.
John

 

[NormanB]

Hi John

Sorry I assumed we were starting from square one! :wink:

I am afraid I am not familar with the VW Passat (although I had an old one (1975 model) yonks and yonks ago.

The symptoms you describe do sound strange, almost if there was a bubble of air blanketing the thermostat and distorting its opening setting - sounds b**ll**s though so ignore my ramblings.

Have you tried the Honest John site you may hit a knowledgeable Passat owner or techie, directly :http://www.honestjohn.co.uk/forum.

Good luck

 

[dieselman]

In this cooler weather it is possible that the heater could be cooling the engine sufficiently.
Try running with the heater off for a while.
It is also possible that the water pump is breaking down or not being driven properly since the timing belt was removed / refitted.

As long as the engine doesn't overheat then there is no real problem. It actually sounds like everything is operating within specs.

 

[john lang]

Thanks Dieselman - last time I took the thermostat out I checked that the impellor was firmly attached to the water pump spindle - you can reach it through the thermostat housing.
In fact, I've done so many things to get to the bottom of this I think it may well be that there's nothing wrong.
It just doesn't feel right to have a rad and bottom hose that are nearly always cold.....
John