Cavitation

[john.p.clegg]

On my return from Stoneleigh a recurring problem again reared its ugly head...cavitation....I believe.

At revs above 3500 the heater starts to blow cold not hot air,I seem to remember the word cavitation for this phenomenon but does anyone know what causes it and better still how to cure it as the weather is starting to turn cold and next week is Newark Autouumble and it's bound to be chilly...

Thanks

John

[stuartgb100]

John,

This may help with an explanation of "cavitation".
It's a Triumph-stateside link:

http://www.team.net/sol/tech/coolant.html

Regards,
Stuart.

[john.p.clegg]

Hmmmm.....interesting but not my problem methinks,maybe I have the wrong word?

John

[types26/36]

Sounds like its been "overcooled" .......fit a thermostat with a higher opening temp. ...........you do have a thermostat in?

[tower of strength]

sounds like you have air in the system to me, I had a similar problem on a special i built a few years back, I ended up running the car with the front end up on ramps, squeezing various hoses till the air bubble ended up in the header tank!! It took quite a while but was succesful

mark

[types26/36]

John, what is the temp gauge showing when the cool air is been fed into the car?

[bcmc33]

My first thought goes to the point of fill when these type of problems appear. To address this potential problem, I fitted the filler housing from Ford that fits on at the thermostat position. This results in the fill being at or very near the highest water point, and should give the system the best opportunity to bleed air. It?s not good practice to have the fill level point half way down the system.
Cliveboy does a thermostat housing specifically for the Elans.
If you already have this type of housing fitted ? then I shall be very interested in knowing the the failure mode of your problem.


Brian Clarke

[1964 S1]

Sounds like a thermostat problem to me.
A bit of cardboard blocking part of the radiator fixed the same problem in our old Peugeot 505, I removed it in the summer. Does the heat fade occur mostly during highway driving? It may be too much water circulating too rapidly and the increased air flow at speed through the radiator cools it too much.
If it is a cavitation problem, you can try running with the radiator cap loose allowing bubbles to vent. Just make sure it doesn't overflow in stop and go traffic, or after you shut the engine off.

[john.p.clegg]

The temp.guage reads normal so I assume that somehow the pump is not pumping hot water to the heater matrix but O.K. to the radiator,I suppose bleeding the system of air will be the next job ..
As for the stat,that seems to be opening and closing O.K.

Will bleed the system and report back after Newark...

John

[rgh0]

Problem may be a fouled heater core. The plus 2 mixes cold and hot air with a constant hot water flow through the heater. If the heater core is fouled you just dont get enough water to create hot air to mix. Could also be in part due to misadjustment of the dampers in the heater so that the cold air is not shut off enough even when heater set to full hot

If the thermostat is fully open the pressure drop available to drive water through the heater is also at its lowest and this also increases the problem of a fouled heater core.

regards
Rohan

[john.p.clegg]

Thanks all..
Re-furbished the heater box last winter,flushed out the matrix and made new flap seals for the flaps so should be as good as new,all I can think of is that at a certain speeds the impellor is just stirring the water rather than pumping it round the heater circuit,but having said that there is no sign of overheating so the pump must be working as a pump at least via the radiator..... Maybe there is something re the pressure drop when the stat. is full open....

John

[tdafforn]

obvious thought (And I'm sure you've checked this..)
But is the heater supply pipe being kinked?
Tim

[Dave-M]

Possibly a faulty rad cap allowing overflow bottle to fill, dropping level to a point where water is below heater pipe connection on cyl head. As it cools down water is drawn back and all appears OK. Temp guage still reading OK due to metal temp of head?
Don't know for sure but must be a possibility.
Regards
Dave

[theelanman]

cavitation is a water thing........
rya power boat instructor speaking....
but probably not the onfo you want!!!.