Expansion/header tanks

cappers · Nov 18, 2021

The 3.5V8 efi transplant in my 90 uses the original 2.5P lozenge shaped brass expansion tank like the tdi's.

The bottom outlet is blanked off and the top goes to a V8 rad. Originally the bottom hose joined the bottom rad to block return hose. The overflow pipe is there.

I have acquired f.o.c a later black plastic Disco tank with 2 outlets like the brass one, but no overflow pipe.

Can I blank off the larger outlet in the plastic tank as in the brass one or is is better to use the large outlet to join to the bottom hose from the rad to the block? Will there be any merit in doing this? Does the lack of the overflow pipe matter?

As it is the temp is always spot on, 83*C and have no coolant issues although filling and burping it can be a chore.

Cheers in advance.

Hicap phill · Nov 18, 2021

Quick Q.
Have you a T piece in the lower radiator pipe to allow water into the system?
Only asking as I use the same metal header & use the lower large outlet to keep level correct

cappers · Nov 18, 2021

Hicap phill said:
Quick Q.
Have you a T piece in the lower radiator pipe to allow water into the system?
Only asking as I use the same metal header & use the lower large outlet to keep level correct

There was a T piece in the hose from the rad to the block but not now.

Screenshot 2020-09-08 at 11.09.17 copy.png

I think that's the reason for it although mine seems to work ok without it but wondered of its best to T-in the bottom outlet? If so I need one of these...

Hicap phill · Nov 18, 2021

Yes T into the bottom with that hose.
Unsure how those plastic tanks overflow. Think it’s through the cap which releases the pressure.
Some fit the RR caps so they get a low water warning light

marjon · Nov 18, 2021

If it works fine now, why try and fix it

.

J

cappers · Nov 18, 2021

marjon said:
If it works fine now, why try and fix it .

J

Good question!
It was given to me by someone who thought it would be better than the brass one.
My main Q is whether the bottom tank outlet and T piece to the rad bottom return hose is actually required as mine seems to cool and function without them ok?

Hicap phill · Nov 18, 2021

Even on my V8 that bottom outlet was connected.
How does your cooling system replace the expanded water that goes into the tank?

old cars used to have the small pipe as expansion & when car cooled down it would suck the water back. Now this is ok as there pipe went to the bottom of the expansion tank, unlike yours

cappers · Nov 18, 2021

Hicap phill said:
Even on my V8 that bottom outlet was connected.
How does your cooling system replace the expanded water that goes into the tank?

old cars used to have the small pipe as expansion & when car cooled down it would suck the water back. Now this is ok as there pipe went to the bottom of the expansion tank, unlike yours

I inserted some tube inside from the spigot to the bottom of the tank as it wouldn't syphon back into the rad without.

I might go for the new tank and plumb it in to the rad return hose pukka-like.

discool · Nov 20, 2021

If u intend to use the later 3.9 onwards expansion tank u will need a port from the top of your radiator then use the bottom hose which u have shown in #3. So now a small hose from the top of the rad and the larger T hose from the bottom hose will fit.
The 3.9 have two hoses from the top of the rad one to the expansion tank the other if the hot flow which goes over to the plenum, the return from the plenum disappears into the inlet manifold on my 3.9, so we have is call a closed circuit cooling system which vents when necessary via the expansion filler cap valves (pressure/vacuum) with an overflow hose hanging from the tank or even from a rad below the rad cap.

I can’t remember a hose layout or even going into the top of the 3.5 I had… but its a long while ago, so must go and have a look in my RR manuals

cappers · Nov 20, 2021

@discool
Thank you that helps.
Currently with the brass expansion tank, the bottom outlet to the bottom rad hose is blocked. All the other hoses are as in the diagram including the two small hoses from the top of the rad (it's for a V8), one to the throttle body and one from the expansion tank. There is also an overflow pipe.

The plastic tank doesn't have an overflow, and the cap is rated at 15psi.

I still don't know whether the brass tank set up as it is as it works ok or plumb in the plastic tank.
If so do I need the bottom hose outlet or not? I'm still unsure about its role; is easier filling, better circulation, prevention of air locks? Is it an improvement or an unnecessary change?
Thanks for the advice.

discool · Nov 20, 2021

Ok cappers I’m going back in time with three photos I’ve just taking from my RR parts catalogue.
First is the vertical looking tank which is just a remote radiator header with connection to the rad and overflow, possibly an upgrade, from the days when the radiator was combined with a header tank and just had an overflow pipe hanging at the side, don’t know why, a redesign of rad maybe.

Then the other two, both now have a tank connection to the radiator bottom hose as well as a hose to radiator, the earlier one still has an overflow pipe.

The last one the tank doesn’t have a overflow pipe and has a screw cap fitted with two valves as fitted to the RR 3.9 and my D1 so now a close circuit cooling and self venting system.

The first expansion tank photo appears familiar so possibly that style NTC4084 was fitted to my 1987 3.5RR

So is it not possible your expansion tank works ok just the port for the bottom hose connection has been blocked as in ‘not required’.

That’s about it with expansion tanks

cappers · Nov 20, 2021

@discool
Great, many thanks.

discool said:
The last one the tank doesn’t have a overflow pipe and has a screw cap fitted with two valves as fitted to the RR 3.9 and my D1 so now a close circuit cooling and self venting system.

That's exactly what I've got off a D1 3.5 V8.
The bottom rad to block hose has a redundant thermoswitch housing for an electric fan (I went back to viscous) so I can remove the switch and put in a 22x1.5mm spigot and some hose to the bottom outlet from the tank to make a CCC/SV system.

The hose from the tank will be closer to the rad than standard (midway) but that shouldn't matter.
Should make filling and air purging easier as it will be through the expansion tank rather than undoing the radiator cap.

discool · Nov 20, 2021

Thats a good plan and I see there’s no reason to change it. Unless u wish to use is a temp sensor.
On my D1 the bottom hose is so close to the rad and there’s a manufactured cutout in the fan cowling so it will fit at the base of the radiator, between the rad and the bottom hose as a 3.9 does…

Your cowling is of course is different, but mine goes to the bottom of the rad and crosses over to the other side below the fan, which has a viscous coupling the whole lump has to be removed before the cowling can be pulled out.

Anyway your bottom hose looks very accessible and nice and clean as well.

Also something i didn’t mention is ,that if u do fit the black expansion tank the max coolant level is up to the half way mark , thats the external seam, around 1.5 litre is just above so leaves plenty of room inside the tank, you know that.
Plus the re-filling with new coolant… if done slowly will or should help in releasing any possible air blockage in the cooling system. But I expect u know that also.

Expansion/header tanks

cappers

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