The V8 Owners Forum -

I've got a 1987 Defender V8 which overhheats. During normal everyday driving the temp guage never gets above quarter and is fine. As soon as I go off road, low box, low speeds it overheats. It has twin Kenlowe fans which work fine. If I leave it to idle, as soon as the temp guage gets to half the fans cut in and it takes 2 minutes to get the temp back to quarter the and the fans cut out. The system isn't pressurised so I don't think the heads are warped. It doesn't leak water and doesn't need topping up. Help!!

monty2556 wrote:As soon as I go off road, low box, low speeds it overheats. It has twin Kenlowe fans which work fine.

Hello Monty,

I think you problem is right there - low speeds = poor coolant circulation..

Even tho' the fans are fine, you still have to have effective coolant circulation to give the fans something to cool, so I reckon your system need a good flush thro' forward and reverse to get all the silt from the radiator and other parts of the system.

If that fails, assume the same problem is caused by a worn out water pump - ie poor circulation.

Hello Monty,

Sounds to me as if the radiator may well be partially blocked, that is to say sediment accumulation within the core.

Ideally the radiator would need to be removed from the vehicle and chemically cleaned.

I feel confident that such a procedure will cure your overheating problem.

Ron.

Any chance the water pump could have too big a pulley on it?

TC

As Ron says it sounds like the Rad is full of gunk. Just another thought have you fitted a big sump gaurd? just it could be there is not enough air flow through the rad because the air can't get out of the engine bay, if that is the case the fans can't help. Or if you have a great big winch infront of the rad, again it could reduce the flow.
Best regards
Mike

Presume this is a "current" problem

so you're probably running the cabin heater


For a quick fix turn the cabin heat off - no water circulation through it that will push all the water through the rad - it may help in a "get you home situation"

But I agree it sounds like the rad probably needs flushed.

Don;t forget that after flushing you need to make sure you get all the bubbles back out the system - PITA on my car

Ian

Many thanks to everyone who replied. Great help.

Monty