Mystery disappearing coolant

Engine Oily Bits, Ignition, Fuelling, Cooling, Exhaust, etc.
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Sloppy 2000
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Re: Mystery disappearing coolant

#41 Post by Sloppy 2000 » Mon May 15, 2017 9:23 pm

This thread has been a little outdated now but I will see if you can help or are still alive even. I have bought a new recored radiator 3 Cores x 52. It has been tested to 35psi. It therefore is an uprated one. The thing it it looks slightly different from mine, being as it has a more rounded top profile. I suspect although being told is compatible for a MK1 it is actually from a mk2. There were differences in recommendations of caps between the two.

Some of you seem to know quite a bit about caps. I am wondering whether to fit the cap that fits best, or keep to a 7lb as the mk1 is prone to head gasket leaks (who knows). Incidentally, do the necks of the radiators differ. In that the overflow header pipe is at a different level in each radiator neck. Would a 13lb realistically put any strain onto the cooling system, the pump or head gasket. Why did manufacturers not stamp the radiator with the type of cap pressure required. I would do if I made radiators.

I wonder what is important, the radiator neck and therefore the temperature/pressure that works the expansion bottle or whether you select the right cap for the engine coolant pressure. I am such a worrier.

Perhaps another good question is why do the books recommend different caps. Is it due to different radiators, or different engines?

Such a muddle :(
Jeff Mk1 Estate
White Triumph 2000 estate mk1 1968
Triumph 2.5PI Valencia

Clifford Pope
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Re: Mystery disappearing coolant

#42 Post by Clifford Pope » Tue May 16, 2017 7:41 am

Back to first principles:

The purpose of a pressurised cooling system is to permit running at a higher coolant temperature, because the boiling point of water increases with pressure.
The running temperature is determined by the opening temperature of the thermostat. So if you select a higher temperature thermostat, the engine will run hotter, and there will be an increased likelihood that in circumstances where the temperature rises substantially above that base setting you risk the coolant boiling, so you need a higher pressure cap to contain it.

Modern cars run at 90 degrees or more, so caps tend to have higher pressures. Very old cars weren't pressurised at all, and ran very cool. The Triumph comes somewhere in between, and I think later models have a higher temperature than earlier.

I don't really know the pros and cons of each, but my instinct is not to push limits, and to use the lower temperature thermostat and lower pressure cap. If something does burst, you get a more spectacular and disabling coolant loss with a high pressure. :)

Paul64
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Re: Mystery disappearing coolant

#43 Post by Paul64 » Fri Jun 09, 2017 3:46 pm

You could of course go to Evans Waterless coolant - no water = no pressure for the pump seal or pipes to handle. As there's no water, there's no corrosion so no silting up of the heater...
I changed my car over at the beginning of the year to see if it worked - no problems so far and it's true; you can take the cap off after a hard, fast run and there's no pressure what so ever.

Paul

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