Monitoring coolant pressure??

[99t]

My RX7 seems to like springing leaks in the cooling system, and in fairness all the hoses are the 1992 originals so far as I can tell, so a new set of hoses throughout is obviously the first job to attend to.

However, given that rotary engines really don't tolerate overheating and a fair proportion of the rebuilds I've read about online seem to have been triggered by a coolant loss episode of some sort, I was thinking how best to monitor such an event?

The reason I'd like to monitor coolant pressure is because once coolant is lost in any significant quantity, the coolant sensor will run dry and so will then only register temperature increases via the thermal transfer of heat through the block etc., and so by the time the sensor registers a significant change in temperature at its location, the hottest parts of the engine could well be fried.

Coolant pressure should, I believe, drop (from normal warm levels) as soon as a significant amount of coolant is lost, thereby potentially giving earlier warning of a problem before serious overheating occurs?

Question is, how to monitor the fairly low levels of coolant pressure? Initial thoughts are an oil pressure warning light switch plumbed into the cooling system and connected to a small additional warning light. I think the pressure switches are usually designed to activate the warning light when sensing below around 4 psi, so this would cause the light to illuminate from cold and hopefully go out when warm and the system pressurises, then if it lights again during driving then this could indicate a problem..?

Obviously some trial and error with different switches might be needed to find an activation level below normal operating pressure, to prevent false alarms, but in theory could this work? Fundamentally would an oil pressure switch survive when subjected to coolant instead?

Any other suggestions welcomed

Thanks
Mark

[Milky Bar Kid]

Whilst I'm not sure how it works, or where in the system it fits, MGF/TFs can be fitted with a low coolant level alarm to help avoid any warping in case of HG failure. I'm not sure that a pressure system would be that helpful, as if you're losing coolant and what's left heats up, it should stay at whatever pressure you're rad cap is. Or what ever pressure the old hoses can cope with!

The other thing I can think of is fitting another temp sender somewhere lower down so it's going to be wet pretty much regardless of water levels. Ok, it might read lower than the usual one, but that can be accounted for. It's only a change that you're looking for rather than an actual figure.

[99t]

Milky Bar Kid said:

Whilst I'm not sure how it works, or where in the system it fits, MGF/TFs can be fitted with a low coolant level alarm to help avoid any warping in case of HG failure. I'm not sure that a pressure system would be that helpful, as if you're losing coolant and what's left heats up, it should stay at whatever pressure you're rad cap is. Or what ever pressure the old hoses can cope with!

The other thing I can think of is fitting another temp sender somewhere lower down so it's going to be wet pretty much regardless of water levels. Ok, it might read lower than the usual one, but that can be accounted for. It's only a change that you're looking for rather than an actual figure.

I agree to a point, if the rate of coolant loss is low then pressure loss will be minimal initially, however I'm looking for warning of a more catastrophic loss of coolant, and judging by the most recent one on my car, the system had lost pretty much all pressure very quickly - luckily I spotted steam as soon as it happened and was able to switch off before damage was caused.

The RX7 does have a low level warning, but it hasn't activated on my car when coolant has been lost quickly - possibly it isn't working so that is something I can check too..

The idea of a second temp sensor low down is a possibility, thanks

[Marf]

Simplest suggestion would be a t-peice in one of the coolant pipes with a pressure sensor screwed in feeding a pressure gauge that reads 0-1bar.

You could look into designing a circuit which reads the pressure off the sensor and triggers a light if it goes below xxpsi, but it'd be more work.

[anonymous-user]

best suggestions are: ;-)

1) header tank with float sensor - std on most cars these days, has reed switch and float in header tank, level drops, switch closes - put large lamp on dash that says "STOP NOW !!!"....... (there is a nice round VW part that works well on other cars - see eurocarparts etc

2) fit CHT (cylinder heat temp" sensor instead of coolant temp sensor - requires drilling and tapping to your engine in some sensible location, but would immediately show any cooling system porblems - sensors availible for aircooled cars, so 911 unit would work for example (ect sensors typically only read to 120degC max, CHT sensors read up to 150 = 160 degC)


(The problem with the "Pressure sensor" is it will only read when the engine is warm and the system has expanded / increased vapour pressure)

Edited by anonymous-user on Friday 29th October 14:25