how can a BHG cause overheating?

[kingmick]

you will find you had to much air in the system i would say.

[nb86]

to answer the orig. question.
the combustion gasses overheat the coolant and reduce cooling capacity.
i actually had a 4age blow a head gasket. it was running 12:1 comp ratio though...
now i have a falcon which is doing the missfire on startup, doh.
usually overheating results in a blown head gasket, not the other way around.

[SL666]

the combustion gasses overheat the coolant and reduce cooling capacity.

i find that kinda hard to believe, if you were getting enough combustion gasses into the water jacket that it was doing that, im pretty sure overheating wouldn't be the first sign.

[mtp_69_i]

you'd blow a radiator/heater hose OR spray coolant into the overflow.

my mum cooked a mazda 929 not long ago. Cracked the head so bad the motor spat coolant about 6 feet out of the radiator top when cranking the motor.

[kingmick]

to answer the orig. question.
the combustion gasses overheat the coolant and reduce cooling capacity.
i actually had a 4age blow a head gasket. it was running 12:1 comp ratio though...
now i have a falcon which is doing the missfire on startup, doh.
usually overheating results in a blown head gasket, not the other way around.

lol confussed about the" not the otherway around" as over heating is just one thing that blows a head gasket or makes it creep, so a bhg from other things beside over heating can make the water over heat.

[SL666]

but HOW does as BHG cause overheating?

[kingmick]

by hot combustion gasses tracking into water system.This is why you hear"check for bubbles in water system" etc

suppose i should add it can also track water into the chamber and you loose water with a seep so less water in the system so over heating aswell.

[EldarO]

combustion gases, CO3 etc. etc. aso degrade the ethylglycol in the coolant, so the coolants rust-resistant capabilities suffer.

Eldar.O.

[mtp_69_i]

CO3?

carbonate? HCO3

[amichie]

but HOW does as BHG cause overheating?

Mostly by displacing the coolant. If you take a healthy car and drain coolant it will also overheat. I have had two MX83s over the years and both have had BHGs. Both would not overheat until the coolant level dropped.

[SL666]

okay, so everyone agrees that a BHG can only cause overheating by displacing the coolant?

[kingmick]

i can see you read what i wrote!lmao

[buddha]

Just a related question from a mechanical novice ... is it possible to avoid a BHG altogether, or will they all go eventually?

And apart from overheating, what else will cause a BHG?

Cheers.

[SL666]

detonation, and bad design.. some engines just do them eventually, G200 Isuzu's when pushed because there's not enough meat between the cylinders, ea falcon 6's coz they are crap.. and 7m's because of some other deficiency..

The basic stuff really, don't let your engine ping, and don't let it overheat... and don't stuff 40psi of boost into a stock engine - but if you do that and lose only the headgasket you would be pretty lucky.

[RObErT_RaTh]

and 7m's because of some other deficiency..

Nothing wrong with the motors, just weren't torqued to a high enough spec from factory. Something to do with changing the gasket material at the last minute I believe.