Pressurising the coolant system for testing

Hi,
A question of principle: When I pressurising the coolant system for testing, is there a difference when I'm doing this with cold/warm/hot engine?
Example: I know there is the small and large cooling circuit, do I test also the large part when engine is cold?
Thanks and best
Mario

Hi, what do you mean by "presurising the system", how would you do that?

You can get pumps to put on the expansion tank or radiator cap to pressurise the system.
I don't know anything about small and large cooling circuits, only familiar with one circuit to cool the engine as a whole and heat the cabin.

Doing it cold with the engine off is a great way to find any small leaks.
Doing it with the engine up to temperature is the best way to find any internal problems like failed head gasket, cracked head or block etc

kermit_rr said:

I don't know anything about small and large cooling circuits, only familiar with one circuit to cool the engine as a whole and heat the cabin.

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It's more complex than that. On a Td5 the coolant circuit is fully completed only when the thermostat is open or if the engine is cold the flow will be "larger" only above 1500rpm when the mechanical bypass valve opens but the radiator still bypassed, on a cold engine at idle the coolant circulates only in the lower circuit through the block and heater core, the radiator and top side of the circuit are bypassed. So if you want to check for leaks with cold engine you must keep rpms above 1500 untill the thermostat opens, only then the radiator comes into play too.

sierrafery said:

It's more complex than that. On a Td5 the coolant circuit is fully completed only when the thermostat is open or if the engine is cold the flow will be "larger" only above 1500rpm when the mechanical bypass valve opens but the radiator still bypassed, on a cold engine at idle the coolant circulates only in the lower circuit through the block and heater core, the radiator and top side of the circuit are bypassed. So if you want to check for leaks with cold engine you must keep rpms above 1500 untill the thermostat opens, only then the radiator comes into play too.

Click to expand...

Cheers for that. Sounds like the designers used to work on p38s

I want to test with something like this Amazon product
Currently it looks like that I'm loosing water from the water pump itself and something in the hight of the motor cooler which I cannot see while pressuring the system. I read also about the two paths of the coolant system and it sounds like I've to repeat that with some engine revs....

Thought I'd chip in with my experience.
I had an intermittent water loss on my TD5, I was in the habit of checking water and oil levels every few days.
No water in the oil, no obvious leaks, sometimes it didn't need topping up for weeks, other times it was every few days.
I tried using the U.V. leak detection method, didn't show much.
In the end, I changed the water pump which had done 350000 km and was the original one.
Cured the issue! But I didn't find anything obvious wrong when I changed it.
Could just have been the O rings on the water pump, there are three of them, I changed these at the same time.

I will replace my water pump in the next days....