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Mike Noc · 20th March 2012, 19:37

Good start TC but I think you need to add the fuel cooler, thermostatic valve and the associated pipework to the diesel circuit, because when the fuel is cold I don't think it returns to the tank but stays in a closed loop circuit, with the ITP topping up what is taken by the HP pump to fuel the engine. Overspill from the ITP returns to the tank during this time.

If you look closely at the circuit there isn't a simple bypass of the fuel cooler to the tank, and the way it is piped, taking into account the different pressures from the returning fuel and the ITP, it diverts fuel straight back to the UBP which gets it up to temperature in cold climates alot faster, then as everything warms up the thermostatic valve starts to open to regulate fuel through the fuel cooler and back to the tank.

One other point is that with a failed UBP the engine stops. The ITP can't supply fuel past the UBP. A good UBP will run fine with a failed ITP with enough fuel in the tank, although it has more work to do.

The system is a bit more clever than it looks!

Mike

20th March 2012, 19:37	#3
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,547 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	Good start TC but I think you need to add the fuel cooler, thermostatic valve and the associated pipework to the diesel circuit, because when the fuel is cold I don't think it returns to the tank but stays in a closed loop circuit, with the ITP topping up what is taken by the HP pump to fuel the engine. Overspill from the ITP returns to the tank during this time. If you look closely at the circuit there isn't a simple bypass of the fuel cooler to the tank, and the way it is piped, taking into account the different pressures from the returning fuel and the ITP, it diverts fuel straight back to the UBP which gets it up to temperature in cold climates alot faster, then as everything warms up the thermostatic valve starts to open to regulate fuel through the fuel cooler and back to the tank. One other point is that with a failed UBP the engine stops. The ITP can't supply fuel past the UBP. A good UBP will run fine with a failed ITP with enough fuel in the tank, although it has more work to do. The system is a bit more clever than it looks! Mike Last edited by Mike Noc; 17th August 2014 at 22:10..