CDT overheating

[karthiks]

Originally Posted by SD1too

I agree that the thermostat is a suspect, but in the 75/ZT it is unconventionally mounted in the radiator return hose to the engine. Therefore it's the temperature of the bottom hose (containing the bleed screw) which needs to be felt.

Simon

Hmm the Haynes manual states that the top hose should be the one checked if the thermostat opens. Weird

[SD1too]

Have a look at your own hoses and see which one leads to the thermostat.

Simon

[karthiks]

Originally Posted by SD1too

Have a look at your own hoses and see which one leads to the thermostat.

Simon

I am confused too actually. I thought the bottom one was were the thermostat was. I'll have to grab both hoses, I guess

[T-Cut]

I believe this is the coolant flow diagram for the diesel.





The diagram forms part of the discussion on the diesel thermostat failure mechanismhttp://www.the75andztclub.co.uk/foru...d.php?t=102943

TC

[karthiks]

Originally Posted by T-Cut

I believe this is the coolant flow diagram for the diesel.

The diagram forms part of the discussion on the diesel thermostat failure mechanismhttp://www.the75andztclub.co.uk/foru...d.php?t=102943

TC

So, which pipe (bottom/top) should I be touching to figure out if the thermostat is working properly?

[karthiks]

Observations:

I went for a ride to heat up the engine. Stopped when it reached 80. Top pipe to radiator and expansion tank are hot. The entire radiator is cold.

I hope this helps narrow down the diagnostics

[FrenchMike]

Another view:

Cooling system.jpg

Circulating pump ?

Mike

[karthiks]

Originally Posted by FrenchMike

Another view:

Attachment 25184

Circulating pump ?

Mike

Is that the water pump?

[FrenchMike]

Originally Posted by karthiks

Is that the water pump?

No,here it is in 15:

[T-Cut]

Yes it could be the pump has lost the impellor, it could be a silted up radiator, but I suspect the thermostat has seized 'shut'. The latest diesel stats are prone to failure (premature opening - not what you have here), but the earlier ones remain a mystery (to me anyway). What year is the car?

Here's that diagram again.



Report this image

The colour of the arrows does NOT indicate temperature.

The stat is located at the water pump inlet and controls two flow loops using two coaxial valves. When the stat is cold (stat 'shut'), it allows full flow through the heater circuit, but blocks flow out of the radiator (bottom). When the stat is heated from the hot flow from the heater, it opens the radiator valve and throttles down the heater loop. If the stat is seized 'shut', it will only allow flow through the heater loop and the radiator won't have circulation. The main outlet hose from the head will get very hot by coolant conduction and convection.

With a fully operational thermostat and very hot coolant entering at the top of the radiator, there will be a thermal gradient down to the bottom. Coolant exiting the bottom will be at a significantly lower temperature than at the top, but it certainly won't be cold.