Coolant cap worked itself loose?
Today I was on the motorway and of course being glued to the temperature gauge, I noticed as soon as it started to go up above normal. Fortunately I was near an exit junction and was able to merge into the first lane and slow to 60 and put the cabin heater on full. As soon as I did so, the temperature dropped back down to normal. It did get to about 3/4 for a few seconds. I pulled over as soon as I could and checked the coolant tank. The level was normal but I could hear a slight hissing. I (safely) checked the coolant cap and it was very loose. I tightened it back up and drove home (about 15 miles) and everything was fine and the cap remained tight, although I only did a couple of miles at 70mph, the remainder being 50/60.
So can the coolant cap work itself loose like that? Perhaps I erred on not over-tightening it and it just needed to be tighter. Or could something else still be wrong and caused this to happen? I.e. will it happen again??
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With a kit like this you 1st fit the suitable adapter in place of the coolant pressure cap and use the pump to pressurise the cooling system to @ 12 - 15 psi and look for leaks and see that the system holds pressure without the needle on the gauge dropping.
Then you use the appropriate adapter to test the cap in the same way.
"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"
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- Airportable
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And he has a lathe that’ll swing a greater diameter than mine. At my age that’s about it for size envy.
M
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- David Aiketgate
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Replied by David Aiketgate on topic Coolant cap worked itself loose?
Posted 1 week 3 days ago #208478David
:shrug:
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this process can be found in the workshop manual or it the howto section of this site.
"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"
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- David Aiketgate
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Replied by David Aiketgate on topic Coolant cap worked itself loose?
Posted 6 days 5 hours ago #208578I've been trying to make sure I don't still have any air in the system. When I run the engine with the coolant cap removed, the coolant level gets higher and higher until it gets near the top of the tank and I then turn the engine off before it overflows. Instructions I have seen say it should go down as air is removed. The coolant remains high until I bleed the radiator which drops the level to where it should be. Is this normal or does it mean there is a blockage or something with the radiator??? Instead of removed air, I seem to be introducing it? Could such a blockage have cause the overheating, resulting in a loose cap?
David Aiketgate wrote:-
For our purposes we can take it that liquid doesn't expand when heated (it does but not significantly). The only reason your coolant level will rise substantially is gas in the cooling system. Gas expands dramatically with temperature! Obviously a worki g pressure cap will reduce the expansion but the level will rise substantially. With the cap off, the rise will be dramatic!
This gas can be trapped air or combustion gases! If it is air you should be able to eventually bleed it out, if it is combustion gases from a failed head gasket it will be continuously reintroduced whenever you run the engine.
The quickest test that can determine which it is, is a sniff test that any garage will be able to do for you. They draw the gases above the coolant in the expansion tank through a liquid with a blue coloured indicator. If combustion gases are present, the liquid turns yellow. Then your bank balance turns red!🫣
David
:shrug:
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- Airportable
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I’ll be under it later changing one of the coolant pipes & I don’t anticipate any problems. One good burp from each bleed point & forget.
I have however swapped the original MGR header for a VW design, that shouldn’t make a difference other than it might not ingest as much air when refilling.
M
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