Thread: 6 cyl series 3 radiator cap question

the series cap can use either but the recuperation tank will only work with a cap that has the 2 seals.

without the top seal if your recuperation tank is full OR the feed line to it is full then the coolant will be expelled past the cap. OF more dire consequence is that if the top seal is missing then the systme will not recuperate as it cools and eventually you will expel enough coolant to potentially hit a low cooland condition (if you can look into the filler neck and the coolant does not cover the cores then you are low on coolant in a series).

you can use pretty much any generic radiator cap that fits that is rated to 14psi. normal system pressure should only be about 7psi at normal operating temp.

Originally Posted by Blknight.aus

you can use pretty much any generic radiator cap that fits that is rated to 14psi. normal system pressure should only be about 7psi at normal operating temp.

From what I've read the original caps are rated at 4psi. The replacement in Repco's catalogue is also 4psi. From what you have said that seems pretty low if 14psi is what you suggest as a replacement.

I'm running a 186 with the original landy radiator and I think even the 186 conversion manual suggests 9psi rather than 4. Could this be why my expansion tank never seems to circulate, never seems to suck water from the tank when the radiator level drops?

atm the missing top seal will be stopping it from drawing off the recuperation tank.

at 4psi Its probable that its pushing so much coolant out that its flowing out the overflow of the tank and being lost forever.

Originally Posted by pfillery

From what I've read the original caps are rated at 4psi. The replacement in Repco's catalogue is also 4psi. From what you have said that seems pretty low if 14psi is what you suggest as a replacement.

I'm running a 186 with the original landy radiator and I think even the 186 conversion manual suggests 9psi rather than 4. Could this be why my expansion tank never seems to circulate, never seems to suck water from the tank when the radiator level drops?

There are two types of cap in all of the various pressure ranges.

With the plastic recovery tank you need to have a recovery cap, the type with a second spring loaded valve in the cap (as pictured above). The expansion or header tanks on vehicles like Range Rover have the regular cap.

With a recovery system the cap needs to seal on the rim of the filler as well as on the top of the radiator tank. You also need to confirm the recovery system is not blocked or have any air sucking leaks between the reservoir and radiator.

So in the spirit of series landrovers and the ability to fix them using a coat hanger and duct tape, I spent 90 cents on some neoprene rubber from Clarks and made a new seal which works beautifully. Will check the level tonight when I get home but looks good so far.

So what is the reason for the different pressures of the caps? Sorry, dumb question I know. One cap I have is a 4psi and the other is 10psi, obviously the 10 has a stronger spring. But why the difference? And also while I'm on the stupid questions, why the difference when you convert to a holden 6? Is it just that the original landy motor runs a much lower pressure?

Originally Posted by pfillery

So in the spirit of series landrovers and the ability to fix them using a coat hanger and duct tape, I spent 90 cents on some neoprene rubber from Clarks and made a new seal which works beautifully. Will check the level tonight when I get home but looks good so far.

So what is the reason for the different pressures of the caps? Sorry, dumb question I know. One cap I have is a 4psi and the other is 10psi, obviously the 10 has a stronger spring. But why the difference? And also while I'm on the stupid questions, why the difference when you convert to a holden 6? Is it just that the original landy motor runs a much lower pressure?

Higher pressure rated cap gives 1. higher boiling point, 2. higher stress on hoses/radiators/heater cores. So unless you are using 14psi rated Holden radiator and heater cores I would stick with the 4 psi cap.

The thing is that the cap pressure doesn't do something magic inside, it is a relief valve setting at which it releases some expanding air/vapour/steam to keep the pressure at that point or below. Pressure reduces water loss through vapourising, but old Landy radiators weren't designed to hold higher pressure than 4 psi so don't push your luck.

This is an old vehicle, you are supposed to check the water daily, not shut-bonnet-and-forget for 10,000km between services.

The increase in pressure increases the boiling point of the coolant,3 deg.F per LB,so as engine operating temps increase so does the cap pressure and the boiling point
A few thing need to work together,
The way the different parts of the cooling system are made,with older radiators and heater cores the two flat sufaces of the tanks are just soldered together,they doent stand much pressure,then they changed to the V shaped lip on the core that the tank is soldered into it,later on plastic tanks are clamped together
The termostat also has to match the required operating temp and cap pressure
The size of the radiator has to deal with the heat generated
So an early non presurised system boiled at 212 deg.F
Increasing op temps improved efficiency so 4LB cap system can run up to 224 deg F and so on.
With the changes so the recovery system(over flow bottle) came into play,and I think that all pressure systems should run this.
So your holden powered landy should work with a 7 or 9LB recovery cap and a 180 deg C thermstat increasing the pressure may lead to cooling system component failure