rad cap

right,, car was overheating on the odd occasion, so i have changed the water pump the thermostat,back flushed the rad and change some suspect pipes (4.6 v8 lpg). no smoke no crap in oil and antifreeze dont smell of exhaust gas. dont seem to be over pressuring but still losing a very small amount of water, about 1/4 a pint in a week.. done a 100 mile trip on sunday and checked water when it had cooled and was spot on,, this morning she is down about 1/4 pint again !!

noticed that the rad cap is hissing when i turn off the car is this normal?

robp38 said:

right,, car was overheating on the odd occasion, so i have changed the water pump the thermostat,back flushed the rad and change some suspect pipes (4.6 v8 lpg). no smoke no crap in oil and antifreeze dont smell of exhaust gas. dont seem to be over pressuring but still losing a very small amount of water, about 1/4 a pint in a week.. done a 100 mile trip on sunday and checked water when it had cooled and was spot on,, this morning she is down about 1/4 pint again !!

noticed that the rad cap is hissing when i turn off the car is this normal?

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First of all i would change the cap. Cap should not leak until the pressure in the system exceeds 15 psi. Each pound of pressure on cap increases boiling point of water in system by 2 degrees F. So instead of the water boiling at 212 degrees F it boils at 242 degrees F. If the engine is heating and pressurising the system enough to escape through cap, you should see this on the temp gauge. If you don't see this on temp gauge then it can only be a faulty cap releasing before it should. Part of that release will be water vapour so over time you will lose water.

I am nominating Wammers for the most concise and accurate answer of the year award.

AND, he uses english instead of metric!

wammers said:

First of all i would change the cap. Cap should not leak until the pressure in the system exceeds 15 psi. Each pound of pressure on cap increases boiling point of water in system by 2 degrees F. So instead of the water boiling at 212 degrees F it boils at 242 degrees F. If the engine is heating and pressurising the system enough to escape through cap, you should see this on the temp gauge. If you don't see this on temp gauge then it can only be a faulty cap releasing before it should. Part of that release will be water vapour so over time you will lose water.

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makes sense to me

just ordered a new cap hopefuly thats gonna sort her out.. the wifes waving a box of matches at my Rangie. had to restrain her after she broke a nail opening the glove box

Just out of interest - does the system still have pressure if you remove the cap (carefully) after the car has stood overnight?

norseman said:

Just out of interest - does the system still have pressure if you remove the cap (carefully) after the car has stood overnight?

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no why

robp38 said:

right,, car was overheating on the odd occasion, so i have changed the water pump the thermostat,back flushed the rad and change some suspect pipes (4.6 v8 lpg). no smoke no crap in oil and antifreeze dont smell of exhaust gas. dont seem to be over pressuring but still losing a very small amount of water, about 1/4 a pint in a week.. done a 100 mile trip on sunday and checked water when it had cooled and was spot on,, this morning she is down about 1/4 pint again !!

noticed that the rad cap is hissing when i turn off the car is this normal?

Click to expand...

Hi robp38,

Just to chip in with my recent experience on my 2000 4.6 Vogue, occasional overheat, occasional hissing rad cap. As I had only owned it a few days, went back to dealer, they changed thermostat (had a hole in it), still same problem, back to dealer to change head gaskets, but they said they had already done them before selling to me! Ok, so they pressure tested cylinders... the dreaded cracked block. So now happy with a very smooth recon engine and no cost to me at all. I was lucky it happened straight after buying it. Good luck .....