Adding an expansion tank to a RV8

[rich112]

Further to exploring the cooling system on my Rover 4.6, it has no expansion/header tank.

There is a filler with a pressure cap and overflow pipe in the hose from the water pump to the top of the rad. (marked in red)

But no expansion tank or header tank.

If you fill the system brim full, it just empties a load out of the overflow hose once the engine gets warm.

I think there needs to be an expansion tank.

There's a plugged hose at the top of the rad (circled in green). Would this be the best place to attach an expansion tank? Then I can just replace the existing cap with a bit of hose and fill the system from the expansion tank.

[stevieturbo]

You could use that into a sealed container with a pressure cap ok. Ensure the new tank is at the highest point in the system, and no need to ovefill it.

When cold even just a visible amount in the bottom and that allows the rest for expansion without risk of chucking anything out.

[garrycol]

You could use the same system that the RV8 in a FC 101 has - the expansion tank is mounted down by the chassis so at the same height as the bottom of the radiator. The expansion tank is outside the 'pressurised' area and is connected to the radiator header via a pipe. As the coolant expands any excess lifts the seal on the radiator cap and allows the excess to flow to the expansion tank. However when the coolant cools it creates a vacuum in the system and the radiator cap allows the fluid in the expansion tank to be sucked back into the radiator.

The radiator coolant is topped up through the radiator cap and not the expansion tank.

Garry

[ChrisJC]

You've got a couple of options here, and they require different radiator caps!!

Option 1 is an expansion tank, which can be anywhere, above or below the radiator cap. This needs a cap with two seals. The 'overflow' pipe runs into a bottle of fluid, specifically to the bottom of the fluid. When the engine heats up, the coolant expands, forces past the lower seal on the rad cap, and ends up in the bottle. When the system cools down, it sucks it back in, which it can do because the upper seal is present. The expansion bottle is not pressurised and is open to the atmosphere (through a cap!). This is like a Series Land Rover.

Option 2 is a header tank which itself is pressurised. It has to be the highest point in the system. It is basically part of the system so your rad cap would just be a top seal only, no pressure valve in it. The overflow pipe would go into the bottom of a header tank, which has the pressure relief rad cap on it. This is like the SD1, or Range Rover P38.

Chris.

[stevieturbo]

Option 2 is always the better option.

Of course it can always be operated with an overlow reservoir too. But a sensibly done header tank is maintenance free and easy.

[rich112]

You could use the same system that the RV8 in a FC 101 has - the expansion tank is mounted down by the chassis so at the same height as the bottom of the radiator. The expansion tank is outside the 'pressurised' area and is connected to the radiator header via a pipe. As the coolant expands any excess lifts the seal on the radiator cap and allows the excess to flow to the expansion tank. However when the coolant cools it creates a vacuum in the system and the radiator cap allows the fluid in the expansion tank to be sucked back into the radiator.

The radiator coolant is topped up through the radiator cap and not the expansion tank.

Garry

Yes, I believe that's technically what as expansion tank does as opposed to a header tank. I'd never even noticed that a radiator cap has a return valve as well as an over pressure valve.

I could attach a simple container to the existing overflow hose. It has to be vented to the air and the overflow hose has to go right to the bottom of the expansion tank so that it's always covered and the engine coolant can get blown in and sucked out as it heats and cools.

[rich112]

You've got a couple of options here, and they require different radiator caps!!

Option 1 is an expansion tank, which can be anywhere, above or below the radiator cap. This needs a cap with two seals. The 'overflow' pipe runs into a bottle of fluid, specifically to the bottom of the fluid. When the engine heats up, the coolant expands, forces past the lower seal on the rad cap, and ends up in the bottle. When the system cools down, it sucks it back in, which it can do because the upper seal is present. The expansion bottle is not pressurised and is open to the atmosphere (through a cap!). This is like a Series Land Rover.

Option 2 is a header tank which itself is pressurised. It has to be the highest point in the system. It is basically part of the system so your rad cap would just be a top seal only, no pressure valve in it. The overflow pipe would go into the bottom of a header tank, which has the pressure relief rad cap on it. This is like the SD1, or Range Rover P38.

Chris.

Thanks Chris.

I see that the header tanks on Car Builder Solutions have three ports. The outlet has to go into a tee on the bottom rad pipe, the inlet goes to the top rad bleed pipe and then there's the overflow to the road or an expansion tank.

There are pretty cheap aluminium tanks online with just an outlet and overflow too.

[stevieturbo]

As you have no inherent self bleeding ports in the system, the additional port on the round one is of no use to you.

But whether you hook the lower port to the bottom hose ( ideal ), or somehow access that bung on the top of the radiator, makes little odds.

And if you wanted as an additional, yes you could also run an overflow from that header tank too. But there should be no need.

[ChrisJC]

You've got a couple of options here, and they require different radiator caps!!

Option 1 is an expansion tank, which can be anywhere, above or below the radiator cap. This needs a cap with two seals. The 'overflow' pipe runs into a bottle of fluid, specifically to the bottom of the fluid. When the engine heats up, the coolant expands, forces past the lower seal on the rad cap, and ends up in the bottle. When the system cools down, it sucks it back in, which it can do because the upper seal is present. The expansion bottle is not pressurised and is open to the atmosphere (through a cap!). This is like a Series Land Rover.

Option 2 is a header tank which itself is pressurised. It has to be the highest point in the system. It is basically part of the system so your rad cap would just be a top seal only, no pressure valve in it. The overflow pipe would go into the bottom of a header tank, which has the pressure relief rad cap on it. This is like the SD1, or Range Rover P38.

Chris.

Thanks Chris.

I see that the header tanks on Car Builder Solutions have three ports. The outlet has to go into a tee on the bottom rad pipe, the inlet goes to the top rad bleed pipe and then there's the overflow to the road or an expansion tank.

0027248_vertical-header-tank-rear-bracket.jpeg

There are pretty cheap aluminium tanks online with just an outlet and overflow too.

71s4ra1JqnL._AC_SL1500_.jpg

Yeah they are both header tanks and must be at the highest point. The main difference is the lack of a rad bleed input, which is an application specific detail - you might need it, or you might not. You do need a bleed from the highest point to let any air into the header tank though, somehow.

Chris.

[rich112]

I got one of the basic header tanks to try out, which has an outlet but no inlet. I can add one easily enough.

Trying to find somewhere to put it, that's at the highest point is a litle tricky but for now I may just put it on top of the radiator.

Adding an inlet to the header tank and attaching it to the top bleed on the rad would be fine, but the orginal filler and top rad hose are higher that the top of the rad, so this makes a good place for an airlock?

Maybe the header tank inlet should go the where the current filler overflow is, as its the highest point? I could replace the old filler with a straight section and a small tee off in the top.

[stevieturbo]

Mount a bottle off the the drivers side high up, this will be the new filler. Either from the rad end tank, lower hose, whatever.

Dump that original filler/cap in the pipe, and instead use a pipe with a small 8mm tee at that location as it is a high point and potential air trap, as a bleed vent to the new header

[rich112]

Mount a bottle off the the drivers side high up, this will be the new filler. Either from the rad end tank, lower hose, whatever.

Dump that original filler/cap in the pipe, and instead use a pipe with a small 8mm tee at that location as it is a high point and potential air trap, as a bleed vent to the new header

Getting a tank in, up at the top of the bulkhead under the scuttle is going to need a custom tank as there's not much room. Agreed, its the best spot though!

Yes, a tee where the filler is now, would defo be the highest spot.

[rich112]

Here's the ideal location:

Just need someone to modify the tank....

A TR7 one might do the trick, I think these are brass so will clean up nice. They are orientated the right way to slip into the same spot and have all the right pipes on.

[unstable load]

The Classic Minis had a virtually identical tank, but it stood "upright" with the filler cap at almost right angles to that one, maybe worth looking at as an alternative for space issues.

[stevieturbo]

Just draw a tank up and have it made, you can get custom stuff done like that fairly cheaply.

Seems plenty of room to have one sit on that box above the brake pipe stuff.