Running with no thermostat

[lukeb]

Can anyone confirm what would happen if you were to run your car with no thermostat, especially in a m30 engine.

cheers

[buster]

the engine will be over cooled so take a bit longer to warm up.No problem in summer but in winter it'll take ages for the heater to get warm.
No detrimental effects though.

[lukeb]

ive been told by a friend that on the m30 engines it goes into a "secondary cooling cycle"? (noy sure what this is) and that the cooling system would only go round half the block. i thought it would run cold, but my friends engine has badly overheated causing the headgasket to go and therefore the big ends, and was wondering if running wth no thermostat would cause this.

[bottlecapE30]

i have heard of this happening on m30 but not m20s my 735i would overheat and the fuel cut of would come on at like 2200 rpm. If you drive the car in the winter at all you will have to keep it or you will never have heat.

[mrLEE30]

running with no thermostat will have the effect of circulating the cooling water/antifreeze through the radiator at all times, where as a thermostat closes the water path to the radiator when the water temp is cold or cool, thus the water is only circulated around the engine block. this lets the engine block warm up quicker, once warm the thermostat opens and the radiator is brought into the system, this balance is kept as you drive, engine cool thermostat closes, warm it opens. in summer it is likely your thermostat will only be closed for the first few minutes after start up, then the engine will remain hot enough for it to be permamantly open. however in winter the thermostat could open and close under normal driving conditions, thus without a thermostat your engine would run cool and over fuel possibly causing bore wash (but this is quite unlikely), you would also have cold toes!

so to sum up... in a hot climate it will have no detremental affect to the engine or its ability to cool.

lukeb, a blown head gasket is normally caused by over heating, if a thermostat sticks closed then the engine would very rapidly over heat. if he did not have a thermostat then it is unlikely this is the cause of overheating, more likely a cooling leak, knackered water pump, viscous clutch on the fan etc etc.

mrlee

[lukeb]

cheers for the replys but my mate found something on the e28 forum.

in the m30 engine they run a different cooling system, with the thermostat in it runs normal, but if it is removed then the coolant follows the path with the least resistance, thus being that the coolant just goes round and round the block, and not into the radiator. with most engine types this does not happen and the coolant still flows through the radiator. Obveously another over complicated design by BMW

cheers for the help anyway, its apreciated as always

[mrLEE30]

now that is interesting, and logical too! I wonder if the M20 will suffer from same symptoms if run without thermostat?

mrlee

[Brianmoooore]

! I wonder if the M20 will suffer from same symptoms if run without thermostat?
mrlee

Yes it will.
Running any engine without a thermostat will be detrimental.
On many BMW engines it willl alter the flow characteristics, and, even if it doesn't allow the flow to bypass the rad, it will likely reduce the flow past certain areas of the head and lead to local hotspots.
In any case, all engines have an optimum running temperature. Too hot is bad. Too cool is bad, and if you run without a stat it willl be one or the other most of the time.