My recent purchase

[classicgreendog]

HI,

I recently purchased FPF 678B. 1964 408. Vin number : 408 7043.

It is not in a good state. It has suffered from a bit of neglect and needs some TLC.
I have begun to re-commission it, but it will take some time. I want to get it
on the road shortly and use it through the summer as a 'running resto'.
Next winter I hope to get it re-sprayed

I need some advice. Can someone tell me what the pressure the radiator cap should be please ? It isn't fitted with an overflow bottle, and it blew out 2
core plugs.? I found the wrong thermostat was fitted. It seems to build up pressure but doesn't release out of the rad cap ?

I don't have a manual.

Many thanks.

[Kevin H]

Apparently, according to this thread Bristol recommend a 15lbs radiator cap.

I would question why it needs to be that high, given several reports of popping core plugs on these engines, but maybe it has something to do with the design of the waterways in the engine.

Of course you need to make sure the valve in your rad cap is actually opening at the correct pressure (not sure how you test that!)

As for the presence of an expansion tank, another 408 owner will need to confirm that. (There is one fitted to the 409 but the 408 Mk2 parts list does not show one. I don't have a 408 parts list).

There is one on the attached pic of a 408 engine bay, but it's doesn't look original.

[GREG]

The radiator on a 408 has an in built expansion tank. When you look through the filler hole you will see a second hole about 5 " below and you only fill with coolant to about 1/2"below the second hole. Sounds like you have been over filling the system.

The manuals are available from Bristol cars and the Bristol owners club.

I have only heard of three of these engines blowing a core plug even at 45 years old. Heard of more core plug problems with 411 's. I wouldn't question the rad cap apart from if it's working ! Try a new one.

Greg

[Rubbond]

My ignorance no doubt but I've never heard of a core plug? The name suggests
it may be to release the sand after the block has been cast. Or maybe a
design feature to prevent the block from cracking if the coolant were to
freeze? Or to assist with flushing the engine?
But in any case, the radiator cap cannot really fail. It's just a
spring-loaded seal that would leak, rather than get stuck. And surely the
radiator core would be the next thing to burst, or the coolant hoses if
cracked.
I have on many occasions had problems with engines overheating (come to
think of it most recently with a vintage outboard engine). It was always the
thermostat, or in the case of the outboard, blocked water channels, but the
steam always came out of the radiator cap. If these cores "pop out" at less
than 15 psi, then might they not just drop out going over a speed bump?
Andrew.

[Kevin H]

Originally Posted by GREG

Heard of more core plug problems with 411 's.

Where did you hear that Greg?

In 10 years of running a Bristol Enthusiasts mail list then web based forum and before that as a member of BOC and BOCA, I can't remember hearing of one 411 losing a core plug!

[Kevin H]

I have started another thread here http://www.bristolcars.info/forums/r...-pressure.html to discuss the topic of radiator caps and why we pressurise the cooling system.

Another thing just occurred to me however given Greg's revelation that the 408 has an integral expansion tank. A modern radiator cap has TWO valves - one pressure activated valve to let coolant out (usually into an expansion tank) once the pressure exceeds the cap's rating. It also has a vacuum operated valve which allows coolant back in from the expansion tank as the system cools. The coolant usually flows out and back in through a pipe in the filler neck where the radiator cap sits. But how does it work on a radiator that has an "integral" expansion tank?

[caspian pugh]

Originally Posted by Rubbond

My ignorance no doubt but I've never heard of a core plug? .

Even my Willie has heard of a core plug - you have a problem.

I have spoken to Butch our mechanic, he tells me that core plugs often rust but electrolytic corrosion between the edge and the block can cause them to loosen and pop with cooling system content pressurisation.

As Greg confirms, Mini core plugs in steel will fit most Chrysler V8 but the best replacements are brass core plugs from the States fitted with a little RTV sealant (non acetic acid cure) around the edge.

Hope this helps,

Cass.

[Sam410]

I'm not sure about the 408, but the 410's expansion tank is under the bonnet slam panel, between the grille and the radiator. Easy to assume there isn't one!

[pasini s]

Hello,


here's where the expansion tank of my 409 is:

http://www.stefanopasini.it/Bristol_...nsion_Tank.htm

Of course I don't know if this applies to a 408 as well....

Cheers

Stefano

[classicgreendog]

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CURRENT MESSAGE FROM: pasini s

Hello,


here's where the expansion tank of my 409 is:

http://www.stefanopasini.it/Bristol_...nsion_Tank.htm

Of course I don't know if this applies to a 408 as well....

Cheers

Stefano



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I'm not sure about the 408, but the 410's expansion tank is under the bonnet slam panel, between the grille and the radiator.. Easy to assume there isn't one!



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---Quote (Originally by Rubbond)---
My ignorance no doubt but I've never heard of a core plug? .
---End Quote---
Even my Willie has heard of a core plug - you have a problem.

I have spoken to Butch our mechanic, he tells me that core plugs often rust but electrolytic corrosion between the edge and the block can cause them to loosen and pop with cooling system content pressurisation.

As Greg confirms, Mini core plugs in steel will fit most Chrysler V8 but the best replacements are brass core plugs from the States fitted with a little RTV sealant (non acetic acid cure) around the edge.

Hope this helps,

Cass.

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[classicgreendog]

[i]

Hi, It's me again.

I thought my problem was resolved but it has re-surfaced, and I have a new query.
On Saturday afternoon I was sitting in a car park waiting to exit when a loud POP was followed by a gush of water and a third core plug had blown.!

I spent all day today re-fitting a new one and checking the thermostat etc.,

The car was running OK - The temperature was sitting nice and steady at 40 degrees, and I had set the Kenlowe to cut in at 45 degrees.

I am mystified.

I let the car tick over until the temp was steady, and made sure the Kenlowe cut in etc., which it did.

I checked the rad cap and it was duly stamped 15 degrees.

However, and this is my query. Having reached operating temperature I was surprised that I was able to remove the rad cap without any pressure or steam blowing out. In fact there was no pressure obvious at all ??

Very different to my Daimler 250 V8 where pressure is very obvious and water is expelled out of the overflow pipe.

Why haven't I got any pressure at the rad cap ? - and is this why the core plug is blowing instead ? The pressure is at the bottom of the engine instead of at the radiator top ?

Any ideas guys ??

Regards,
MIKE

[GREG]

Was the car stood a long time before you bought it? I am wondering if it's corrosion from being stood so long with no antifreeze, but sorry , no real answers for you !

I hope it's sorted now

Greg

[412usa]

Mike,

Have you checked if the thermostat is clogged shut? This could build up
pressure in the block.

Peter

[David Olivant]

If you have sufficient pressure to blow a core plug, but no pressure at
the radiator cap, there are perhaps two reasons
One .- excess pressure from a head gasket/block.
Two:- Blockage to or at the radiator.
Check the thermostat and the bottom of the radiator. If both are blocked the
core plugs take the brunt of the pressure.
Hope this helps and happy digging.
David

[Kevin H]

Originally Posted by classicgreendog

[i]
However, and this is my query. Having reached operating temperature I was surprised that I was able to remove the rad cap without any pressure or steam blowing out. In fact there was no pressure obvious at all ??

Well it sounds like there is pressure in the block, so to my mind the logical conclusion would be a blockage. Maybe one of the waterways in the block?

Was the top of the radiator hot?

This situation would make me very nervous. Imagine if you lost a core plug while you were driving along and didn't notice!

Kevin

[classicgreendog]

Thanks Guys,

I have fitted a new thermostat, and I fear you could be right, but nothing
is obvious. The car has stood for 3 years or more and it has blown before I bought the car. The underside of the bonnet and the top of the engine show signs of heat by way of crackled paint etc.,
The top of the radiator does get hot.

I took the car for a 15 mile run this morning and it behaved perfectly.
The temp gauge held perfectly steady at 80 degrees in and out of traffic.

regards,
Mike

[Rubbond]

If you still have the old thermostat, wife permitting, you can easily check
if it is/was working by putting it in a pan of water and bringing it to
boil.
At least you will know if a faulty thermostat was a contributing factor.
I would at least take off the top and bottom radiator hoses, and flush both
radiator and the engine seperately. See what comes out.
Good luck!
Andrew.