The curious case of the hot V8

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meles meles

meles meles

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I have a 3.9 litre normally aspirated V8 in a short wheelbase Land Rover. It's fitted with an Edelbrock manifold and Holly carb. The engine has just been stripped, rebuilt and put back in the vehicle, but now has a heating problem.

After a couple of minutes of running the top hose is pressurised and extremely hot, but the radiator and bottom hose remain cold. The expansion tank then gets very hot and the pressure release valve vents. There seems to be no flow of liquid through the cooling system, either by convection or being forced through by the pump. I've removed the thermostat, removed checked and replaced the water pump, checked the radiator. All are fine. If a hosepipe is connected to the top hose of the radiator, water can be squirted all round the engine block and exits at the water pumpoutlet.

From this, I assume:

  • There is no blockage anywhere in the system
  • There is no reason why the pump shouldn't be pumping - it's in perfect order and turns when the engine is running
Anyone got any suggestions?

##
 
No steam, and no airlock.

The system has been filled slowly, from the bottom, several times. Water flows freely through the radiator and the engine block when a hosepipe is connected to either. When the system is closed and the (fully functioning) water pump is relied upon to provide the flow, flow doesn't seem to happen.

*skratches ikkle kranium in kompleet bafflement*
 
Thats right the only item that moves the coolent around the engine is the pump and u have replaced that, as I would have said that the impeller shaft sheared ie. the pully is going around but not the impeller.

Have the small hoses that go to the expansion tank been fitted the correct way round and is the cap a good one.

If you run the engine without the cap fitted the coolent should overflow as the engine heats up.
 
The main thing that will stop circulation is an air bubble in the system causing the pump impeller to run in air and cavitate.

Has the water system got any air bleed piping? as on the later Discos etc.

If you run the engine with no rad cap, as Discool says, it should slowly push the water level up as the water temperature rises, but are there any bubbles in there as well?

Have you a flange-mounted thermostat, and if so, does it have the air-bleed toggle in the flange? Not all are fitted with it, and air is trapped below the 'stat' without it.

Peter
 
The thermostat has been removed completely - the Landy will be used for expedition work in North Africa so isn't likely to need one ! Cooling, or lack of it, will be a big issue though. If the lid is removed from the expansion tank then it does indeed bubble - though only a little - and then overflow - whilst the radiator remains completely cold.
 
meles meles said:
The engine has just been stripped, rebuilt and put back in the vehicle, but now has a heating problem.

After a couple of minutes of running the top hose is pressurised and extremely hot, but the radiator and bottom hose remain cold. The expansion tank then gets very hot and the pressure release valve vents.

  • There is no blockage anywhere in the system
  • There is no reason why the pump shouldn't be pumping - it's in perfect order and turns when the engine is running
Anyone got any suggestions?

##
Click to expand...

The symptoms sound like classic head gasket failure; why was your engine stripped and rebuilt? Have you run a compression test?

If you think it is an air lock, try raising the vehicle at the front on the side of the expansion/header tank (use a ramp/kerb or whatever) remove the cap and let it idle, make sure the heater is on full hot and see if that helps it.
 
The problem resolved itself in the end. I drove the vehicle to the end of the drive, turned it around, reversed it back into the garage. When I got it there I noticed the radiator was warming up and the temperature was reading normal. It's worked perfectly ever since. I can only assume that there must have been airlock somewhere that we couldn't locate, but that a short drive cleared it.
 
Whilst the best minds available are thinking about cooling problems....

I have 90 with a 3.9 / carbs fitted. The temperature runs just hotter that the previous engine - instead of the needle pointing at 12:00 O'Clock it points at 1:00 - runs fine but just indicates a bit hotter.

I am assuming that either the water pump is not working perfectly or could the radiator be not working so well - I am thinking the water pump as the previous engine (std 3.5) ran fine.

As the water pumps aren't so expensive (compared to a head gasket) would anyone recommend just changing it?
 
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