Thermostat pictures

[widdowson2008]

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 ??

Honest opinion? No.
Yes - they amount to the same thing but it's the bypass from the head getting throttled rather than controlling flow to the radiator. Two entirely different things.
Think about it this way - What is the highest priority - engine or radiator?
Gotta be engine.
I'm not at home at the moment so aint got access to data, but there is now absolutely no doubt in my mind what is being protected.
Basically, from the logged data, what is happening is that the heater circuit is staying at a consistent 65 ish. This is the ONLY circuit at the stat which is in constant flow.
Coolant from the head (via the bypass) mixes with the heater circuit, and when this mixture reached 82C, the stat begins to open. At this point, coolant begins to enter the stat from the radiator, retarding the overall temperature mix.
Initially, the balance of the bypass/rad flows is biased toward the bypass.
As the stat opens wider, the ratio between head/rad shifts, becoming biased toward the rad.
The stat is now in 'hunt' mode as the mixed temperature attempts to stabilise.

Gotta go - England have just scored - Andy Murray will be so p**sed off.

[haydn callow]

'fraid that's a bit complex for me.......surely what happens is.....the stat stays shut whilst the engine gets up to temp and the heaters get all "snuggy warm" then this circuit hits the "magic" 82, starts to open the stat and the radiator then takes over and makes sure things don't get out of hand. Seems simplezzz! to me or am I missing the point.

[widdowson2008]

'fraid that's a bit complex for me.......surely what happens is.....the stat stays shut whilst the engine gets up to temp and the heaters get all "snuggy warm" then this circuit hits the "magic" 82, starts to open the stat and the radiator then takes over and makes sure things don't get out of hand. Seems simplezzz! to me or am I missing the point.

Hi Haydn
Thats exactly what I (and many others) thought until I started getting accurate results from Helen. What blows this way of thinking clear out of the water is the fact - repeat FACT - that the heater return circuit (including top up temp from expansion tank) never got above 65C. ie:17degC too low to operate the stat.
However, the stat DID open and the bottom hose DID get warmer, so it looks very much like it is the bypass that is doing the stat opening with the heater circuit acting purely as a governer.
Hope this is a bit clearer. Need to get home and use MY computer. The kids have crap machines.

[haydn callow]

'fraid I must be a bit thick....isn't the "bypass" circuit.....cylinder head to top of rad...top of rad to expansion tank....Ex tank to heaters via the top of stat......when this reaches 82C the stat starts to open......?????? my ex tank and heater hoses certainly get up to 82C...or am I missing the blindingly obvious ???

[missfixit70]

I think what Steve means by the bypass is the recirc from the head to the top of the stat, I think we are in danger of arguing about semantics here when we all basically agree on how the cooling system works. the stat is controlled by a mix of the heater returns (which include the header tank returns) & the recirc form the head into the top of the stat.
Interesting observations from my multiple bleedings recently - if you switch the heaters on full in high heat when the engine temp is above @60-70 degrees you'd expect it to bring the top hose temp down as it extracts heat from the system wouldn't you? This is not the case, as you extract the heat from the heater circuit, it means the heater returns cool down thus lowering the average temp controlling the stat, closing it down, thus accelerating the rate the temp of the engine increases. So putting the heaters on is possibly not the best thing to do when you want to dump some extra heat as it looks like this closes the stat & actually makes it run hotter. Makes sense to me anyway

[patnben]

Basically, from the logged data, what is happening is that the heater circuit is staying at a consistent 65 ish. This is the ONLY circuit at the stat which is in constant flow.

Your conclusions regarding return temperatures make no mention of the total heat content.
If you are only measuring the temperature then basically your data is flawed. You have to
measure the total volume of water flowing in the circuit and to do that you need to know
it's velocity. There is a great deal of difference in thermal energy between water travelling
slowly in a circuit and water travelling at high velocity.

It is a relatively simple matter to calculate the pressure loss in any circuit, it's
proportional to it's length and inversely proportional to it's diameter. I have no intention
of doing that as I trust that Mazda would have got it right in the first place. However
I could make an educated guess at what they may be in terms of the pump volume.

My guess is that the two heating circuits and the turbo cooling circuit account for about
20% of the pump volume. If you measure the main by-pass length and diameter, and the radiator
circuit parameters you may be surprised to find that both circuits have a similar pressure
loss when passing 80% of the pump capacity. This has to be so, the thermostat is acting as
a simple 3 port mixing valve and to avoid excessive hunting the port pressures should be
roughly balanced.

In my original post, I was concerned with the by-pass port closing completely during a warm
spell in the summer. In these conditions I would not want any hot air from the cab heating
blowing over my body so there would be very little heat loss in the cab heating circuits,
combine this with the fact that the turbo cooling circuit is heating the circulating water
then the overall effect of these three circuits would be almost zero and exist only as a
permanent by-pass circuit which would do nothing to cool the engine.

So, we are left with 80% of the pump volume which has to go somewhere. When the thermostat
radiator port is closed, this volume is flowing through the by-pass port. If the thermostat
bulb expands sufficiently to completely close the by-pass port then this volume has to travel
round the radiator circuit. A healthy Bongo radiator is more than capable of cooling the
flow to relatively low temperatures depending on the vehicle speed and ambient temperature
but certainly should be no problem in our temperate climate.

My point is, why would the thermostat completely close the by-pass port ?. Shortly after the
radiator port started to open the relatively cool water from the radiator would stop the
thermostat expanding towards the by-pass port. The only time this condition can occur is
when the vehicle is standing still and no air going through the radiator, at that point the
block temperature will rise and the ECU will switch on the radiator fans to assist.

As I said earlier, If the By-pass port closes completely while you are travelling at any
speed then you have lost control of the engine temperature, there is no reserve, the return
water from the radiator is too hot to close the radiator port or the thermostat is stuck
open or the pump impellers have rotted away due to poor corrosion inhibitors or you are
simply trying to haul 8 fat ladies up a very steep hill with a manual gearbox in top gear.
Whatever the cause it's an abnormal condition and will eventually overheat the engine.

[Northern Bongolow]

wow great post .
think i will have to read this several times to digest fully.but again great post.

[Northern Bongolow]

wow again,
BUT
all the above stated imo is what is/should be happening in a new healthy cooling system,the problem as i see it is when you loose 10 per cent eficiency of the rad(crud) 10 per cent down in the old stat,and so on,the stat must close fully the top port to try to (save the engine) if this fails to happen the only things that can assist is the fans,and then up to a point,after that its all over,the weakest link will break.

[bongobaz]

All a bit deep for me, fitted Haydn's[ i alert ] temp maintains itself at around 83 > 85 * goes to 90 when switched off then cools naturally.

[missfixit70]

Agree with what Ben's saying, & very well put , BUT at slow speeds & high loads (as well as stationary & slow moving traffic), ie hauling up a hill in low gear, especially towing a heavy load or fully loaded is going to result in the stat opening fully, closing off the recirc port, forcing the majority of the flow through the rad, which due to the vehicle's motion the airflow will not be great enough to remove the heat. This will still be well within control parameters as you've got all the stages (which we still aren't clear on until ecu interrogation is done) of the rad fans operation. In the uk, especially in this part of the country , this accounts for a lot of the driving conditions & the cooling system in good fettle copes with it fine from my observations & monitoring.

[The Great Pretender]

There is a great deal of difference in thermal energy between water travelling
slowly in a circuit and water travelling at high velocity.

I hope you can get that across................................I failed.

[mikexgough]

I guess we need to consider ALL the previous data evidence of Cooling System temperature and it's usual temperature at given times plus consider the Thermal energy at different given times.....

Now...Keeping it simple.... the message for the NOT so technical should be that if your Bongo is new to you....whether your the 1st UK owner or subsequent..... look after the cooling system by changing your coolant and a genuine thermostat as a minimum..... I would go the extra (personally) and thoroughly flush the system and replace the radiator..... You won't need to worry any more...

[helen&tony]

Hi
TGP...you'll never get anyone to understand the system as long as it goes by the misnomer of "Cooling" system
Air is a cooling system, and highly efficient....water is there as a jacket to keep heat in to aid in maintaining heat, and the whole shebang is controlled by a few cheap components
The technology in an IC engine is Victorian / Edwardian, and is superseded by superior technology , as the relatively cool engines produced for cars are there to use as much fuel as possible
Enter the Bad Taste Bears...the ones that drive around in silver plated German cars, and own strings of racing camels...THEY NEED your cash......Business= cheap and nasty....Science = superior technology...and that ain't a so-called modern diesel
Anyway, for the meantime, we're stuck with it!
Cheers
Helen

[rita]

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

Hi,

The thermostat looks like it has been IN the Barbie..??

[Bongo nads]

bongonads