head/block-warping temps

[dark_knight]

at what temps are you likely to warp your block/head past recoverable levels..? i recently ditched my air-con, meaning the auxiliary fan went with it, but now, i'm getting slow-moving traffic temps of about 92 deg C -- at ~94, the rad fan will kick in as it should. but once on the move, it will drop way down to about 86~84 deg C. is this normal..? & should i be worried..? i live in a fairly hot locale temp-wise and running the stock thermostat set at 82 deg C.

ps: i have an after-market temp sensor thus the reason i'm able to get these very specific readings. interestingly enough, even when the after-market gauge is doing its dance, the stock temp sensor is stuck at the mid-point.. tsk tsk tsk..

 

[Texx]

Those temperature readings are fine, you'll only cause damage if the coolant is allowed to boil. Water boils when it reaches 100°C under standard atmospheric pressure, increasing the pressure surrounding the water will increase it's boiling point. The cooling system in your car is a sealed system and is designed to increase in pressure as the coolant temperature increases. The actual maximum pressure the cooling system will operate at is dictated by the rating of your radiator cap, so if your using a stock 0.9bar rated cap then the boiling point of the water in your cooling system will be increased to approx 111°C, when using a radiator cap with an even higher pressure rating the boiling point of the water will be increased even more.

The thermal transfer properties of water are most efficient when the temperature is just above it's boiling point, it was said to me many years ago that the optimum coolant temperature for heat transfer is 113°C, but how true that is I wouldn't like to say.

So going back to your original question, I would suggest that as long as your coolant temperature doesn't rise above 105°C (allowing for a safety margin and temp. gauge/fan switch inaccuracy) and your cooling system does not have any leaks (this is very important) then you should have no reason to be concerned.

It's when a leak develops, whether it be through a failed headgasket, leaking pipe, dodgy radiator cap or other component, the pressure in the cooling system drops along with the boiling point of the coolant. When the coolant boils all you'll have cooling your engine is a load of hot air, that's when engine temperatures sky rocket out of control and serious damage is caused.

 

[dark_knight]

thanks Texx.. makes a lot of sense how you put it.. running green-stuff coolant with a 0.9bar rad cap. would you recommend i uprate to a 1.1bar cap..? would this be 'safe..R'..?

 

[Texx]

If your rad cap isn't opening and dumping coolant into the expansion tank then there's no real need to change it. Put it this way, your using a 0.9bar cap, it's not opening so (assuming the cap is good) the pressure in the cooling system never reaches 0.9bar, if the cooling system pressure never reaches 0.9bar what's the point in using a 1.1bar or 1.3bar etc... rated radiator cap?!

 

[dark_knight]

after reading your post Texx, i have just spanked myself in the back of the head for not figuring that out earlier.. :!
it doesn't dump but it has on two occasions sipped up some coolant from the expansion bottle -- from the 'full' mark to about 3/4 full. does this mean i didn't properly bleed and so the system took the little deficit that i didn't give it..?

 

[Texx]

The cooling system works on a pressure release / vacuum return basis. The idea being is the cap regulates the maximum pressure, when the pressure reaches the caps rating it bleeds coolant into the expansion tank to maintain the desired cooling system pressure. When the system cools a vacuum is created and coolant is drawn back into the system from the expansion tank. This process ensures the radiator is full at all times. Having said that, the design of the stock radiator is, in simple terms, crap. The header tank is too small and under harsh driving conditions the coolant can boil in the very top of the radiator, the vapour from the boiling coolant escapes past the rad cap and into the expansion tank, this can cause some coolant to be forced from the expansion tank as the level rises, once the 'harsh driving conditions' cease the cooling system temperature and pressure drops and coolant is drawn back into the radiator. Over time this can lead to a drop in the reserve coolant level in the expansion tank without any immediate signs that any coolant has been lost.

Generally you find that the cooling system finds it's own 'normal' expansion tank level and often it's lower than the 'MAX' level found on the side of the tank. As long as the radiator is full and the level in the expansion tank is above the minimum when checked from stone cold, the above shouldn't cause any trouble. It's only when racing the car such as you would during a trackday (where the car is being driven hard for much longer sustained periods of time), that the crap stock radiator can become a real issue.

 

[dark_knight]

it's all good Texx. i've been a good student listening to all you have said..
so back to the original worry, i should just keep my temps from residing past the ~110 deg C mark & i'll be alright, right..