The V8 Owners Forum -

Hi everyone. I'm looking for information on how to simplify the cooling system in my '74 Vauxhall Viva fitted with a Gems 4.6 V8. Can anyone help? It has an E46 bimmer radiator, a Volvo 760 single outlet header tank with small return & a standard heater matrix with an inline shut off valve. Any help will be gratefully received! Cheers. Leigh.

What does your waterpump look like? Every connector on it is an input so one of them can be used for the output from the inlet manifold and the heater matrix. The expansion tank is either just a vent or goes to a catch tank dependent on if you have a two way cap on it or not.

Hi Scudderfish! It only has the radiator connection. It may be possible to add fittings to either It or the front cover. Cheers. Leigh.

The water pump rotates in the opposite direction to the crank. Here's a pic of the rear of the front cover. Cheers. Leigh.

Is there a reason you can't stick to the GEMS layout?

On my Land Rover, I faithfully reproduced the OEM cooling system layout (from a P38 Range Rover), and have had no problems with engine cooling whatsoever.

Chris.

I'm not entirely sure, but I think the P38 has a smaller hose vulcanized onto the inlet hose that leads from the radiator to the water pump. This is the return line for the heater/heater valve.

The line to the heater core comes out of the rear intake manifold.

The heater control valve should be a 3/2-way valve (not a 2/2-way valve).

That means there's always a flow, either to the heater or to the return. There should be a T-piece in the return.

Without it, the engine wouldn't have a small cooling circuit when the heater is off.

Best regards,
Frank

ChrisJC wrote: ↑Sun Jul 06, 2025 1:22 pm Is there a reason you can't stick to the GEMS layout?

On my Land Rover, I faithfully reproduced the OEM cooling system layout (from a P38 Range Rover), and have had no problems with engine cooling whatsoever.

Chris.

Hi Chris! My problem is the bmw rad has larger inlet & outlet to which I have made adapters to link both sizes, plus cost for extra parts is an issue due to this car eating money like it's gone out of fashion!!

Cheers. Leigh.

FBW wrote: ↑Sun Jul 06, 2025 3:09 pm I'm not entirely sure, but I think the P38 has a smaller hose vulcanized onto the inlet hose that leads from the radiator to the water pump. This is the return line for the heater/heater valve.

The line to the heater core comes out of the rear intake manifold.

The heater control valve should be a 3/2-way valve (not a 2/2-way valve).

That means there's always a flow, either to the heater or to the return. There should be a T-piece in the return.

Without it, the engine wouldn't have a small cooling circuit when the heater is off.

Best regards,
Frank

Hi Frank. Thank you for your concise redrawing of my effort! It's very much appreciated & answers my question, however, where would the return from the expansion tank go? Back into the water pump? Another problem is the gems inlet manifold doesn't have a rear outlet, only on the right hand side.

Kind Regards.

Leigh.

It isn't really a return on the expansion, it's a vent for excess. Either dump it or catch it in a bottle and if you have the right pressure cap it'll get sucked back in as the water cools.

Exactly! The expansion tank has no return line.

A hose leads from the highest point on the radiator to the expansion tank. It does enter at the top, but there's a pipe inside, so the line ends at the very bottom of the tank.

If there's air in the radiator, it moves into the expansion tank and bubbles upwards.

If the system expands due to heat, it pushes the air, or, if too much coolant is added, the water, out through a pressure relief valve.

If everything contracts again during cooling, air can be sucked into the expansion tank through a check valve.

However, the radiator always sucks in water through the low-lying pipe.

It's actually quite simple.

Hi guys. Thank you for your replies. I'm running a Volvo 760 expansion tank with an E46 M3 radiator and the standard heater matrix in my Vauxhall Viva HC. The gems 4.6 had the thermostat in the inlet manifold... it may have been in another vehicle before I stripped it for rebuild. It is definitely a gems inlet as it differs from sd1 and classic range rover efi inlets.

Regards. Leigh.

The thermostat housing and inlet manifold base.

That looks good, though. Are those larger funnels?

The thermostat should open at 82°C. The P38's only opens at 88°C, which is too high and bad for the engine.

Does the engine have T-liners?

Oh yes, about the expansion tank. My description referred to the typical Land Rover tank. The Volvo one certainly works the same way. The inlet here is only from the bottom.


Greetings
Frank

FBW wrote: ↑Mon Jul 07, 2025 8:27 pm Oh yes, about the expansion tank. My description referred to the typical Land Rover tank. The Volvo one certainly works the same way. The inlet here is only from the bottom.


Greetings
Frank

Cheers Frank!

Regards.

Leigh.