Following on from here:- http://www.mazdarotaryclub.com/forums/showthread.php?t=67195
Possibly a bit of a ramble, but bear with me, I do have a question or two at the end!! :)
I\'ve replaced most of the coolant hoses now on my 92 fd3s after having three of the originals spring substantial leaks in quick succession - all whilst driving and only by a mixture of good fortune and decent observational skills have I avoided an overheat because I\'ve been able to switch off very quickly each time...
Needless to say, I\'m a bit paranoid about the cooling system now, even though all 3 hoses that failed had good reason for doing so
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- Had been nicked with pliers or similar close to the hose clip (by someone working on the car previously) and had failed where it had a fairly deep chunk taken out of it
- Was rotten - once removed it was obvious the hose was as weak as anything where it had failed
- Standard hose clip had been replaced by a Jubilee which had been overtightened, causing the hose to split internally and eventually all the way through
I\'ve carried out the champagne test at the cap by the thermostat, and was relieved to see no bubbles at all going from a cold engine all the way through to the fans cutting in, just a tiny bit of foaming when the coolant was properly hot.
To monitor against future failures, I\'ve plumbed a 0-15psi "fuel" pressure gauge into the cooling system using a t-piece in the hose to the rear of the throttle body, but the results aren\'t quite what I was expecting...
Cold start & left at idle From cold (0psi) the reading rises quite gradually as the coolant warms up, peaking at around 12psi, at which point there is a sudden drop in pressure (back to about 3psi) and then the process repeats - pressure rises slowly (couple of minutes) to around 12psi and then drops back quite suddenly. Does the same before and after the thermostat opens. Would this be the (0.9 bar) AST pressure cap in operation, releasing pressure to the header tank?
Driving On the road it\'s a different story however, the coolant pressure seems to rise and fall dramatically with engine revs. For example, accelerating from 1500rpm to 5000rpm would see a fairly static pressure reading of perhaps 6psi suddenly shoot off the scale and peg the needle. The speed at which the needle hits the peg would suggest the system could actually be hitting 30psi+!!! :eek: As soon as the revs are reduced the pressure drops back to sensible levels.
Obviously as the revs increase the water pump is spinning faster, but would that be expected to cause such a massive pressure increase?
Any suggestions for possible problems to investigate would be very welcome. I can\'t help feeling these sorts of peak pressures are way too high and would go some way to explaining why the cooling system has seemed to be finding the next weakest link via which to release pressure...
Thanks
Mark