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Anyone ever had a radiator cap fail?

BRE Fabrications LTD

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As the title says, anyone know of radiator caps failing?

My 80 overheated on Sunday. I opened up the bonnet and saw dried up coolant all around the radiator cap. There were no signs of coolant leaking from anywhere else. The radiator cap wasn't letting the system overflow into the overflow bottle. I pulled the cap, amateur mistake i know, which resulted in a fountain of hot coolant and me loosing the radiator cap so I cant check it...
 
As the title says, anyone know of radiator caps failing?

My 80 overheated on Sunday. I opened up the bonnet and saw dried up coolant all around the radiator cap. There were no signs of coolant leaking from anywhere else. The radiator cap wasn't letting the system overflow into the overflow bottle. I pulled the cap, amateur mistake i know, which resulted in a fountain of hot coolant and me loosing the radiator cap so I cant check it...
I've got a spare one lying around if you need it
 
As the title says, anyone know of radiator caps failing?

My 80 overheated on Sunday. I opened up the bonnet and saw dried up coolant all around the radiator cap. There were no signs of coolant leaking from anywhere else. The radiator cap wasn't letting the system overflow into the overflow bottle. I pulled the cap, amateur mistake i know, which resulted in a fountain of hot coolant and me loosing the radiator cap so I cant check it...
Yes, the rubber seal perishes over time.
 
Yep happens all the time, normally the syphon system seizes and stops working.
 
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Rich, its not so much the levels as you would notice odd goings on with the cooling system!

When it happened on the 80, the expansion bottle level never changed, but every time I opened the radiator cap when cold I would have to add a little coolant. Then I noticed when it was cold the radiator hoses would be completely collapsed until I undid the cap. There were a few slightly weepy patches around some of the joints and hoses etc.

It was the radiator syphon valve seized, meaning it couldn't draw more coolant from the tank, or expand into the tank, which was causing the weeping joints as it went over pressure. Changed the cap and it has been fine since.

On a Nissan I had I kept getting leaks, as soon as I fixed one I would get another appear, pipes getting pin hole leaks etc. Expansion bottle kept dropping. That was the same thing, an elderly cooling system and a seized cap, not letting water back out to expand, changed the cap and never had a leak again.

I have put new radiator caps on both my MR2's without waiting for symptoms, I have a new spare genuine cap in the garage also. Saves a lot of aggro! You also can check the pipes are not blocked to the expansion bottle often they fur up with gunge.
 
I wonder if my cap is original then. Both Clive and I cannot keep coolant in our expansion bottles but the rad settles about 1/2” or so down and never moves. Been like it 14 years so it’s not a problem but after reading that I think it may be worth changing.

Got a pic of an original or genuine replacement one?
 
I wonder if my cap is original then. Both Clive and I cannot keep coolant in our expansion bottles but the rad settles about 1/2” or so down and never moves. Been like it 14 years so it’s not a problem but after reading that I think it may be worth changing.

Got a pic of an original or genuine replacement one?

Just to clarify that, my expansion tank is constant at about the 1/2 way line, but the rad tank level is always 15mm from brimming, even when I fill it the level drops, but the expansion tank looks the same.

I had a new rad cap and thermostat fitted about 5 years ago, but willing to change it if this may be a cure...
 
I've always been told to fit nothing else but a genuine radiator cap, this is from family in oz though where the temps get a lot warmer than here in the UK.
 
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The truck has been stood for a couple of days so this is the level cold,

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A lot of crud builds up under the cap, I suppose it also must get washed into the expansion bottle and collected so probably worth washing it out.

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There are 2 seals, the upper one seals the chamber that the expanding water flows through, the lower is the one that keeps the pressure in the radiator and seals the valve that lets it top itself up.

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The pressure valve has a linear spring and opens smoothly with constant pressure on a good working cap.

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This is the valve that lets the water back in when the water contracts. The spring is much softer than the pressure spring.
 
Ahh, that isn’t what I’ve got fitted. We may be on to something here. Time to investigate.
 
Here’s mine.
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Looks like a Japanese after Market part possibly? It’s what was fitted when it was shipped over anyway.

Looks to be much the same.
 
It does look the same. And the tube to the expansion bottle definitely isn't blocked?
 
I don’t think it is but I’ll check.
 
Any leaks whatsoever in the cooling system will prevent coolant being drawn back from the expansion tank, as will soft hoses that collapse as they get old and soft.

Regards

Dave
 
Just checked and my expansion hose isn’t blocked.
 
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