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Radiator Cap Pressure.

551 Views 3 Replies 1 Participant Last post by  Underthebluesky
Hello again.

Today my bottom hose decided to pop off from the engine side. But before that happened, I replaced the radiator cap. The cap is rated at 1.3 bars. The coolant level in the overflow tank prior to this ordeal was just a finger width above max. Coolant does not spill out of the overflow tank.

Driving to a nearby park for a leisurely stroll posed no problems.

However, the journey home was when it happened.

In both situations I drove leisurely.

If my memory serves me right, the specifications of the radiator cap should be between 1.1-1.3 bar.

I also replaced the radiator, top and bottom hoses the thermostat and coolant half a year ago, however didn't replace the hose clamps.

I never had a problem with the bottom hose popping out until today.

So what I'm wondering is...

Who's the culprit here? The new cap or the old clamps? Or both?

Also, while I have your attention, there's a minor leak at the thermostat housing. The housing itself seems fine. Could it be the gasket wasn't seated in properly? I only noticed this recently. It likely has been going on for a period of time, judging by a couple of dried stains.


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Hello again.

It seems like I made a mistake when choosing radiator caps.

The rating range is 0.95 - 1.25 bar, and not 1.1-1.3 bar as I had previously thought.

Perhaps this rise in rating is the culprit.

Higher rating = higher boiling temperature, which in my mind means the coolant is allowed to get hotter before it reaches boiling temperature and so there is more pressure?

I guess what I'm trying to ask is: does a higher-rated radiator cap increase coolant temperature and/or pressure, or does a higher-rated radiator cap allow more wriggle room for the engine because it increases boiling temperatures?
Hello again,

I've just replaced the coolant and the coolant clamps. I've reinstalled the thermostat. I've also bled the system.
The original radiator cap was put back on.

So far I don't see any leaks from the thermostat housing. Nor from the radiator.

However, there's this rhythmic sound, and I think it's coming from the front of the engine.

Here's a video of the rhythmic sound.

Last oil check was last week. No top up was necessary.
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Hello again.

I've just went for a test drive.

Most of the spilt coolant has been evaporated. At the same time, the sound I described in the above post has all but subsided as well, so perhaps it was something to do with that.

No leaks reported.
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