what if your gauge reads 240 but it doesn'r boil over?????? is the gauge bad or what?????

 

not if your rad cap is good and you have no leaks...system is pressurized...makes the boiling point higher.

 

Our gauges (and or sending units) are notorious for being way off. Verify your real coolant temp.

One way is to borrow a IR thermometer and shoot the temp at different places. Like the sensor in the head and at the thermostat housing and see what the difference between that and your gauge reading.

 

or, you could be cheap and lazy like me, and just replace the temp gauge sending unit.... about 95% of the time, that's what makes the gauge read wrong

 

Well, coolent boils at around 212*. Every pound on your pressure cap is worth around 3*. So a 16# rad. cap = 48* + 212* = 260*. So when your gauge hits 260 shut it off.

Auggie

 

Actyally water boils at 212, an Ethylene glycol/water mix will have a higher boiling point. How high depends on your mixture.

 

Well, thats good info. I have a 50/50 mix. What will my coolent boil at without a rad. cap.

Auggie

 

But when should I decide to turn it off at what temp.? Actually mine runs cooler on streets rather than highways If that sounds weird or not?

 

Mine has survived 260 degrees without boiling, with a 16 pound cap and 50/50 Water/Antifreeze. I know the temp was real, as it was a mechanical gauge on the thermostat housing.
Just lucky I guess. Pretty good test for leaks, though!
The factory gauge is very inaccurate.
I can compare readings with the mechanical and sometimes they match, sometimes they're 40 degrees different!
A new sender may help, but it may not.
A bad ground can also give an electrical gauge flaky readings.

I'd try to avoid letting it get over 230, but 240-245 shouldn't kill it.
above that is head-gasket danger zone.
-Rich-