I'm re-routing the cooling circuit on my project truck. The heater circuit has moved.

Normally, a hose comes out of the main cooling circuit downstream of the water pump, into the rigid pipe that runs over the top of the engine, into the heater, back from the heater and into the back of the engine.

I've moved the heater, so now the flow comes off the main cooling circuit downstream of the pump, into the heater, back from the heater into the rigid pipe that runs over the top of the engine, then into the back of the engine.

What does this flow do inside the engine? In other words, if I get a massive airlock in the heater, which bits of the engine will suffer? Does anyone have a functional block diagram of the cooling system (i.e. not the drawing from the workshop manual, but something more abstract that shows what flows to and from where)?

Thanks in advance!

Shameless thread bump - does anyone know the 300tdi cooling system inside out?

I can’t help you I don’t do diesels... but you may possibly get your answer if you post your question in the 300tdi section of the ‘engines’ Forum.
As you can see the disco Forum has moved over more to the troublesome disco 2 threads

I dont know what block diagram from the workshop manual you mean but the attached one looks clear enough to me, what ever you did it's important to keep the flow as it was so if you reverted pipes make sure that the flow goes into the heater's feed pipe(16) from the engine's outlet and from the hetare's return(7) into the pump's hose.

thetim said:

Shameless thread bump - does anyone know the 300tdi cooling system inside out?

Click to expand...

wouldnt matter were you take feed from as long as its on the exit side of water pump and it returns to the inlet side of water pump to ensure flow

Thankyou all - much appreciated. The heater feed's definitely running from pump exit to pump inlet, so will flow - but the routing's longer and more tortuous than the original setup, so I'm concerned about the possible consequences of airlocking it. Clearly the heater won't work well if so; that doesn't bother me so much. With reference to sierrafery's helpful diagram above, I think my key question is - what inside the engine, if anything, relies for cooling on the flow that subsequently outflows into pipe 16?

thetim said:

Thankyou all - much appreciated. The heater feed's definitely running from pump exit to pump inlet, so will flow - but the routing's longer and more tortuous than the original setup, so I'm concerned about the possible consequences of airlocking it. Clearly the heater won't work well if so; that doesn't bother me so much. With reference to sierrafery's helpful diagram above, I think my key question is - what inside the engine, if anything, relies for cooling on the flow that subsequently outflows into pipe 16?

Click to expand...

nothing relies on any flow from 16 apart from the heater,the block and head are hollow ,coolant is directed into the block were it flows back and up through the head to the top hose/thermostat housing like stirring water in a bath with your hand the pump creates a flow if you took the feed for heater from rear of block/head and returned it very close there would be little flow,so feed is one side of water pump ie rear of engine but return is on water pump inlet side

Here's a very basic scheme of diesel engine cooling, that's the general principle:



the heater is on a ''parallel" circuit