Bongo Fury

I have to agree with Bongo nads as far as the thermostat is concerned.
The simple fact is that the job of the thermostat is to modulate the
coolant supply to the radiator. If the temperature rises sufficiently
to close off the by-pass supply then you no longer have any reserve,
maintaining the current conditions will cause the engine to overheat,
either the radiator or the pump cannot cope with the current thermal
energy being produced by the engine.

I would guess that in the UK temperate climate, and a healthy engine
and cooling components, the thermostat would normally modulate between
a third and 2 thirds open and I for one would be extremely concerned if
I thought that the thermostat ever reached a point where it completely
closed off the by-pass supply except when idling in traffic with no air
moving through the radiator.

Once the stat reaches the position of closing the recirc port, it's forcing more coolant through the rad, which then means that the fans (which have several stages of switching, two fans each with two speeds I think) can work more effectively to cool more coolant than with the recirc port still open to any degree.
As Ben says, this is usually in a situation when the airflow across the rad is reduced due to being in slow traffic or sat with the engine idling. This is where the gauge (if modified) will rise up to the point of fans switching on (around 94 degrees) where it will quickly cool down as a good chunk of the coolant is being forced through the rad. If the stat is "lazy" or not able to close the recirc port at this point (which is still well within control parameters) then the fans will switch on, but will only be cooling a small percentage of the coolant, probably not enough to bring the engine temp down as a chunk will still be recircing straight from the top of the hot block into the top of the stat rather than being forced through the rad to be cooled. If this is allowed to continue the temp will continue to rise even if both fans/high speed kicks in, as they will still only be acting on too small a percentage of the coolant.
My observations when bleeding are that the stat (mines a recently fitted mazda stat) closes the top port at @88 degrees as at this point using the funnel/seesaw method, when you rev the engine, the water is forced into the funnel, no matter how high it is held, as the bleed pipe is coming off the cross docking stock at the point where the recirc pipe goes down into the stat, this tells me that route has just closed off. Before the stat opens, revving sucks the coolant out of the funnel, as the stat opens, this lessens in force until the stat closes the recirc port as I describe above.
Just my thoughts/observations

i must say that was well put, and exactly as i see it, that is not to say it is 100per cent right,as we are all still understanding the quirks of the system.keep the input coming in,kirsty loves to type long explanations
keep it up girl.

dave_aber wrote:this is a very polite forum though. Ever visited the singletrack world mountain bike forum?

All those sweaty guys in Lycra..?? No thanks..!

I also think that if Bongo nads is anywhere near land of Mordor, in the fires of Mount Doom & manages to keep his Bongo cool..? I'm interested in what he has to say..!!

... I'm all pointy ears!!

Hi Jay
Quote: All those sweaty guys in Lycra..??

Oh...dunno...sounds interesting

Cheers
Helen

Hi
Here's our old thermostat now its retired and a nice new Mazda one working in its place

It's enjoying a nice spot of sunbathing in the garden, and its just had a nice glass of iced coolant
After a nice spot of lounging , its time for a seat by the barbie

Ah....a retired thermostat living it up
Cheers
Helen

looks like your spoiling that stat,
beach towel! drinks brought to him.has he now got his reward for all his hard work.

Hi Ady
I thought that might amuse
Why do I keep all the old (....)? I've got all manner of rubbish sitting in the yard on windowsills
Cheers
Helen

put them all together round the barby,they may chat,you could then eaves drop on the conversation,who knows they may let the secrets of the cooling system slip out

....especially if you put them in rocking chairs and give one of them a banjo

Hi
Love it!!!!!!
Can I do my Grannie Clampett impersonation now.....JETHRO ...!!!
Cheers
Helen

Yes but !! under the new government retirement rules that stat may have to return to work for up to a further 5 years.!!

Hi
That's just a matter of STATistics

Cheers
Helen

patnben wrote: The simple fact is that the job of the thermostat is to modulate the
coolant supply to the radiator.

Hate disagreeing with folk, but I think you may be slightly off the mark here Ben.
From my observations, I truly believe that the main function of the stat is to get the engine to its ideal working temperature AND KEEP IT THERE. Yes, it modulates coolant to the radiator, but its main objective is to keep the engine and head at workable temperatures. I know this to be true from the data currently to hand (recent/ongoing heat tests on a fully up-to-scratch system.)

From the data, there seems to be two things being strictly controlled by the thermostat.
1 - the head temperature at around 90C
2 - the block temperature at around 65C

When you think about what the cooling system is there for - maintain the engine at optimum working temperatures - it all makes sense.

Ben - what you are saying is absolutely correct with the exception of the above.


Need to get the fact sheet (based on facts) published - so close to completion - just a couple of I's/T's to dot/cross

widdowson2008 wrote:

patnben wrote: The simple fact is that the job of the thermostat is to modulate the
coolant supply to the radiator.

Hate disagreeing with folk, but I think you may be slightly off the mark here Ben.
From my observations, I truly believe that the main function of the stat is to get the engine to its ideal working temperature AND KEEP IT THERE. Yes, it modulates coolant to the radiator, but its main objective is to keep the engine and head at workable temperatures. I know this to be true from the data currently to hand (recent/ongoing heat tests on a fully up-to-scratch system.)

From the data, there seems to be two things being strictly controlled by the thermostat.
1 - the head temperature at around 90C
2 - the block temperature at around 65C

When you think about what the cooling system is there for - maintain the engine at optimum working temperatures - it all makes sense.

Ben - what you are saying is absolutely correct with the exception of the above.


Need to get the fact sheet (based on facts) published - so close to completion - just a couple of I's/T's to dot/cross

Yes !! but doesn't it do this by controlling the flo through the Radiator.....controlling the rad flo and maintaining the working temp amount to the same thing don't they ??