Cylinder head drip

[stonedrive]

Hi Julian, the drips are on the outside edges I’m wandering if I over pressurised when testing like Flying farmer. I put a pressure of 20psi in, no drips before that. Cheers Steve

[jbuckl]

Hi Julian, the drips are on the outside edges I’m wandering if I over pressurised when testing like Flying farmer. I put a pressure of 20psi in, no drips before that. Cheers Steve

That is the pressure for a later car.

[stonedrive]

My stag is a manual 1974. Is it the correct pressure test for mine or should it be less than 20psi. Cheers Steve

[jbuckl]

My stag is a manual 1974. Is it the correct pressure test for mine or should it be less than 20psi. Cheers Steve

All later cars as yours is were 20 psi coolant systems.

some owners have opted to run at 13psi instead though.

you could try that…. Just fit a 13 psi radiator cap…. See what happens.

check / retorque the heads again?

boiling point will be about 97 degrees C at 13 psi instead of 108.8 degrees C at 20 psi

happy place for engines is 90 degrees C ish.

an electric fan can help to prevent any boiling under U.K. hottest days, even at a lower system pressure.

(unless there a bad system issue)

many stags have electric fans these days.

mechanical engine fans were becoming outdated in the mid / late 1960s.

to be fair , they were / are a bit awful, because they are inversely matched to demand…. Hence the viscous drive, which is / was always a bit of a durability issue.

[stonedrive]

Hi Julian, many thanks for info. Steve

[DJT]

Just because it is the Mk2 system with a 20 psi cap, doesn't mean it will be running at 20 psi during normal use. That is the pressure at which the pressure cap will lift, so running at 20 psi would mean the cap was at the point of lifting all the time. I've never checked the 'normal' operating pressure, but I would be surprised if it was much above 10 psi.

[Lingen]

And doesn't water boil at 100 deg C. at sea level? It did when I was at school.
Mike.

[APS]

And doesn't water boil at 100 deg C. at sea level? It did when I was at school.
Mike.

Yes, though air pressure at sea level is 1013.25 millibars, or 14.7 psi. At 13psi boiling point of water is going to be lower than 100⁰C.

I recall my top hose feeling like it was under quite a bit of pressure, but still kept within the limits of the 20psi pressure cap.

[DJT]

Yes, though air pressure at sea level is 1013.25 millibars, or 14.7 psi. At 13psi boiling point of water is going to be lower than 100⁰C.

I recall my top hose feeling like it was under quite a bit of pressure, but still kept within the limits of the 20psi pressure cap.

Something not right there. Are you saying that a hot sealed Stag cooling system at 13 psi is at a lower pressure than the atmospheric pressure outside?

[Philip Wardle]

I think the confusion here is that the cooling system pressure is masured relative to atmospheric pressure, so 13 psi or 20 psi relative to a base of 14.7 psi at sea level.

[DJT]

I think the confusion here is that the cooling system pressure is masured relative to atmospheric pressure, so 13 psi or 20 psi relative to a base of 14.7 psi at sea level.

Correct. Then add in the ethylene glycol, which has a BP of close to 200C, and this raises the coolant BP further to >125C at 20 psi above atm, or >118C at 13 psi above atm. A healthy Stag engine should run at around 90C.

[jbuckl]

The point is, Steve can try a lower pressure cap to help with the drips, maybe.

sorry for posting numbers that fogged the suggestion.
they were only to show the principal and likley consequence.

on a dyno, we used to run curves at 90 degrees c. Cooled via a massive external exchanger system .

it was common to see peaks up to 120 degrees at the end of a curve, when returning to idle…. Even with the over capacity heat exchangers, due to local heat-soak….

the stag does seem to suffer from heat soak peaks, more so than other cars, as the gaydon Soc cooling tests showed…… worth a read; can’t find a link.

[Philip Wardle]

The write-up on the cooling tests is included in this re-print ...

SOC Reprints - 3 & 12 Cooling.pdf

[richardthestag]

could be wrong but testing the cooling system to the full 20lb is simulating an over heat situation, not so very sure that I would test over 15lb and that would only be to test the hoses for leaks. pump it up, leave it for 15 mins and observe. For troublesome systems such as the Rover v8 with leaking core plugs episode I suffered with, I warm the engine up first and then repressurise it to check for leaks.

I wonder if you have a set of those super nasty head gaskets where the gasket material is too thin for the fire rings.

Top hose firming up is a good thing because it indicates that you do not have one of the faulty expansion tanks where the neck doesn't seal to the plastic body.

Top hose firming shortly after start up and when the top hose is still cold is a bad thing as it is possible you have head gasket issues and combustion gases over pressuring the cooling system

While we are on about expansion tanks, yours needs to be no more than half full. when filling the system up for the first time I leave the expansion tank empty, brim the rad through the top hose plug and then seal it. The cooling system will find it's own level, it may need some expansion capacity in the top of the rad as well as the expansion bottle.

before a huge debate starts on ensuring no air in the rad, the mk1 cooling setup with an overflow bottle uses the top of the rad for expansion does it not?

My o-level physics understanding is that, no room for expansion and the system will over pressurise quite quickly and find an exit point, usually the pressure cap but if that has been replaced by gubbins to pressurise the system then I would have thought hose connections might be next but not inconceivable that a weak head gasket will throw in the towel.

Just saying