Was under the car the other day, noticed a silver corrugated thing, kind of like a small radiator under the drivers seat, any ideas? 54 plate TDI Cupra.
It's a fuel cooler.
It cools the hot fuel returned from the engine before it goes to back the tank.
It cools the hot fuel returned from the engine before it goes to back the tank.
The fuel pump is driven by the camshaft, so is always delivering fuel.
Most of the time this will be more than is required, so it gets returned, but it picks up a lot of heat on it's travels through the cylinder head.
Most of the time this will be more than is required, so it gets returned, but it picks up a lot of heat on it's travels through the cylinder head.
Not quite true I know muddy just over looked this, but the fuel tank has a pump which allways pumps fuel to the engine, whats not used goes back the tank via the fuel cooler. Put your hand on it after a run gets quite hot.
And it's positioning under the car isn't ideal for venting. I'm looking at fitting an additional cooler in direct airflow, so the return pipe goes through 2 coolers, not just one. 
And it's positioning under the car isn't ideal for venting. I'm looking at fitting an additional cooler in direct airflow, so the return pipe goes through 2 coolers, not just one.
Many TDI models don't even have one fuel cooler. It's been suggested that this is one reason why some cars get lower fuel economy in hot weather, over and beyond the effects of air conditioner use and loss of intercooler efficiency.
Fuel temp is one input to the ECM, and hot fuel may result in retarded timing. At least that's my understanding, and I could be wrong.
Yes, if it the fuel gets over a certain temp, the ECU starts cutting back.
Can't remember what temp it is, but it's pretty darn hot.
Perhaps there is more than one return ?
The tank pump supplies the tandem pump (on the end of cyl head) which presumably has a return - which I think is the one you're referring to.
But I also thought there was a return from the injectors, as most of the time the tandem pump will be supplying more fuel than the injectors needed. And my understanding was, that it's the return from the injectors where the main heat is gerenated.
If there are 2 returns, wonder if they both go back through the fuel cooler ?
Might be wrong, be interested to know in a geeky techy way though !
I've had a little inspection of my fuel cooler (I spent a couple of minutes with a flat screwdriver opening up some "impact points" ) and there were definitely just two pipes from the fuel tank to the engine - i.e one in, one out. Unless they had hidden one other pipe elsewhere? I doubt it
) and there were definitely just two pipes from the fuel tank to the engine - i.e one in, one out. Unless they had hidden one other pipe elsewhere? I doubt it
I've seen the mod in the Tdi section where you fit a engine bay mounted fuel cooler before the fuel gets to the fuel pump, is there any point in doing this for normal day to day driving?
Ah good diagram, that makes sense. The return from the injectors goes back via the pump and joins the pump return, which all then goes via the cooler.
Great diagram there! Where exactly is the fuel temp sensor which sist between the engine and the fuel cooler? I imagine it must be somewhere on the engine itself?
temp sensor is in fuel return pipe next to duel pump should be rubber hose from duel pump sensor rubber hose metal pipe to fuel filter then return to fuel cooler and then tank. they sometime use the temp sender for the cheep chips you get off ebay
Similar threads
