How "HOT" does it have to get ???

[widdowson2008]

The 'pull-over immediatly' temperature of vehicle cooling systems is not widely understood. The relationship between temperature, cooling, and vent pressure depends on; 1) what the coolant is and its flow rate, 2), the pressure design of the system, and 3) the available temperature drop which depends mainly on ambient temperature, engine load, and whether there is forced or ambient cooling.

If the radiator/expansion cap relief valve is designed for about 1.1 bar - 16 PSI then the maximum temperature at which the coolant should boil is 126 C. This gives you the 'pull-over, dummy' temperature. The coolant system thermostatic valve is not an open/closed switch, but operates over a range. (Modulates) The specified 82C or so at which it starts to open, gives no more than the tiniest flow through the bypass circuit (radiator) , but the 'stat will be fully open by 110C. The engine cooling system is designed to keep the engine coolant galleries somewhere at about 90C for maximum efficiency which it can easily do, even if ambient temperatures of 40C limit the amount of temperature drop across the radiator. Design standards for automobile engines are such that ambient temps of +50C (Dubai in Summer for instance) still allow the engine cooling system to operate.
Older systems with viscous-coupled fans do a good job of shoving ambient air past the engine block, and in those conditions, even in a British summer, the coolant might not go much above 80c. Electric fans are demand driven, providing closer temperature control but often higher coolant temperatures.

If the cooling system is in good order it can run all day at 115-120C coolant, 40-50C ambient without hoses popping, boiling or meltdown. If it's in good order.

In practice sludge forms, limiting coolant flow, rad/ex tank caps let go early loosing coolant, thermostats wilt, coolant contaminants reducing the boiling point, the anti-corrosion additives in the coolant become diluted by tap-water or distilled water top-ups, and hose clips become tired with the expansion/contraction cycles.

If the temperature at the base of the rad (it's a downflow rad on the Bongo) reaches 120C and continues to climb, I would say that that is the point to turn both sets of heater controls to hot, put the heater fans on full, and pull over. If there's no coolant loss, leave the engine running to allow the coolant circuits and fans to operate.

The rad/expansion blow-off cap is a vital part of the system, as you can see, and the only part of the system designed to loose coolant to prevent engine damage. It's worth replacing those when the cooling system is overhauled. However if the cap lets go early, before the 1.1 bar pressure is reached, the pressure reduction lowers the coolant boiling point, coolant loss occurs, and this can lead to engine damage before it's spotted. Coolant pressure loss into the engine block or from a gasket also lowers the boiling point, a viscious cycle from which there is no return.

Specifically, a peak coolant temperature of 107C under load is not a concern, assuming the cooling system is operating.

Beautifully put. Wish I could have picked that wording. The only thing I would change is that the 'stat will be fully open by 96C, not 110C.

[widdowson2008]

I hope you guys don't mind me throwing this n the mix....?!!

I'm thinking; say you put yer new hoses in, new stat, new rad, flush bleed... Basically concentrate on the whole coolant system..? Fit your sensors for peace of mind..

What about the auto box oil & flow to the cooling bit under the radiator?? If poorly maintained would that contribute to remaining abnormal engine temperatures... On hills??

You're right there - it must add heat to the radiator, but only the lower section. However, when you are moving, doesn't the throughdraught remove some of this heat?
And have a think about this - When moving, the top of the rad always gets hot (and stays hot cos its coming straight from the head) The bottom may be warmed by the ATF, but the throughdraught keeps the middle section relatively cool. Now as soon as the stat opens, where does this cooler mid section first travel? Past the ATF. So under normal running conditions with the stat open, the ATF is getting first call on cooling.

[Northern Bongolow]

i would just like to add some actual pressure figures to this very good thread if i may.
as stated above the pressure in the system is very important.
i run an active pressure monitoring gauge /device,and have found the following.

the normal running pressure during light driving is approx half a bar (8 pounds).
enthusiastic driving is 10- 11 pounds.
fans low speed on, pressure is 12-13 pounds.
leaving only 3 pounds pressure left to go for high speed fans (not sure of the pressure switching point of this), then we reach 16 pounds and your coolant is on the floor.

[The Great Pretender]

i would just like to add some actual pressure figures to this very good thread if i may.
as stated above the pressure in the system is very important.
i run an active pressure monitoring gauge /device,and have found the following.

the normal running pressure during light driving is approx half a bar (8 pounds).
enthusiastic driving is 10- 11 pounds.
fans low speed on, pressure is 12-13 pounds.
leaving only 3 pounds pressure left to go for high speed fans (not sure of the pressure switching point of this), then we reach 16 pounds and your coolant is on the floor.

And your heart is in your hand while the other one is getting your wallet out.......................

[widdowson2008]

The 'pull-over immediatly' temperature of vehicle cooling systems is not widely understood. The relationship between temperature, cooling, and vent pressure depends on; 1) what the coolant is and its flow rate, 2), the pressure design of the system, and 3) the available temperature drop which depends mainly on ambient temperature, engine load, and whether there is forced or ambient cooling.

If the radiator/expansion cap relief valve is designed for about 1.1 bar - 16 PSI then the maximum temperature at which the coolant should boil is 126 C. This gives you the 'pull-over, dummy' temperature. The coolant system thermostatic valve is not an open/closed switch, but operates over a range. (Modulates) The specified 82C or so at which it starts to open, gives no more than the tiniest flow through the bypass circuit (radiator) , but the 'stat will be fully open by 110C. The engine cooling system is designed to keep the engine coolant galleries somewhere at about 90C for maximum efficiency which it can easily do, even if ambient temperatures of 40C limit the amount of temperature drop across the radiator. Design standards for automobile engines are such that ambient temps of +50C (Dubai in Summer for instance) still allow the engine cooling system to operate.
Older systems with viscous-coupled fans do a good job of shoving ambient air past the engine block, and in those conditions, even in a British summer, the coolant might not go much above 80c. Electric fans are demand driven, providing closer temperature control but often higher coolant temperatures.

If the cooling system is in good order it can run all day at 115-120C coolant, 40-50C ambient without hoses popping, boiling or meltdown. If it's in good order.

In practice sludge forms, limiting coolant flow, rad/ex tank caps let go early loosing coolant, thermostats wilt, coolant contaminants reducing the boiling point, the anti-corrosion additives in the coolant become diluted by tap-water or distilled water top-ups, and hose clips become tired with the expansion/contraction cycles.

If the temperature at the base of the rad (it's a downflow rad on the Bongo) reaches 120C and continues to climb, I would say that that is the point to turn both sets of heater controls to hot, put the heater fans on full, and pull over. If there's no coolant loss, leave the engine running to allow the coolant circuits and fans to operate.

The rad/expansion blow-off cap is a vital part of the system, as you can see, and the only part of the system designed to loose coolant to prevent engine damage. It's worth replacing those when the cooling system is overhauled. However if the cap lets go early, before the 1.1 bar pressure is reached, the pressure reduction lowers the coolant boiling point, coolant loss occurs, and this can lead to engine damage before it's spotted. Coolant pressure loss into the engine block or from a gasket also lowers the boiling point, a viscious cycle from which there is no return.

Specifically, a peak coolant temperature of 107C under load is not a concern, assuming the cooling system is operating.

Beautifully put. Wish I could have picked that wording. The only thing I would change is that the 'stat will be fully open by 96C, not 110C.

So impressed with binkys post that I misread it.
Binky is TOTALLY CORRECT when he says fully open at 110C.
96 is where the head flow is cut off. Sorry binky.
Once again, brilliant post.

[roofraisers]

Jaylee wrote:-
I hope you guys don't mind me throwing this n the mix....?!!

I'm thinking; say you put yer new hoses in, new stat, new rad, flush bleed... Basically concentrate on the whole coolant system..? Fit your sensors for peace of mind..

What about the auto box oil & flow to the cooling bit under the radiator?? If poorly maintained would that contribute to remaining abnormal engine temperatures... On hills??


I think we need to remember what is heating what,
The pipe for cooling the automatic gearbox fluid runs through the bottom of the radiator.
On a blocked radiator, sediment tends to find its way to the bottom of the radiator with the effect of coolant flow & gravity.
This then leads to the ATF pipe being covered in sediment which act's as a poor conductor of heat & therefore this leads to inefficient cooling of the ATF fluid.In other words, the ATF fluid gets hotter BUT NOT the coolant, so the engine running temperature is unaffected.

The bottom line is that a poorly maintained radiator can increase the running temperature of your engine & your automatic gearbox.
You can overheat an auto gearbox without it affecting the engine temp, because the gearbox fluid couldn't be cooled sufficiently because of sediment in the lower part of the radiator.

To prevent auto gearbox overheating, a secondary oil cooler (oil radiator) should be fitted as these generally use air to transfer heat & not coolant.

Nigel

[Velocette]

Jaylee wrote:-
I hope you guys don't mind me throwing this n the mix....?!!

I'm thinking; say you put yer new hoses in, new stat, new rad, flush bleed... Basically concentrate on the whole coolant system..? Fit your sensors for peace of mind..

What about the auto box oil & flow to the cooling bit under the radiator?? If poorly maintained would that contribute to remaining abnormal engine temperatures... On hills??


I think we need to remember what is heating what,
The pipe for cooling the automatic gearbox fluid runs through the bottom of the radiator.
On a blocked radiator, sediment tends to find its way to the bottom of the radiator with the effect of coolant flow & gravity.
This then leads to the ATF pipe being covered in sediment which act's as a poor conductor of heat & therefore this leads to inefficient cooling of the ATF fluid.In other words, the ATF fluid gets hotter BUT NOT the coolant, so the engine running temperature is unaffected.

The bottom line is that a poorly maintained radiator can increase the running temperature of your engine & your automatic gearbox.
You can overheat an auto gearbox without it affecting the engine temp, because the gearbox fluid couldn't be cooled sufficiently because of sediment in the lower part of the radiator.

To prevent auto gearbox overheating, a secondary oil cooler (oil radiator) should be fitted as these generally use air to transfer heat & not coolant.

Nigel

Doesn't the aircon condensor coil also waft heat straight into the rad to add to the load?

[roofraisers]

Again if the radiator is blocked internally with sediment, the coolant/engines heat isn't being transfered to the air efficiently, so the engine temp won't be reduced.
If the radiator can't disapate heat efficiently, it's hardly going to gain heat efficiently so I think the air con alone won't affect the engine running temp.
If the radiator is working efficiently & correctly, as the coolant travels down through the radiator coils the coolants temperature is reduced by ambient air temperature with the forward movement of the Bongo or the aid of the electric fan before it re-enters the Bongo engine to absorb more heat. Coolant enters the top of the radiator at temperatures in excess of 90*C, I know it's been warm lately but the air temp was always cooler than that, so the coolants heat will tranfer to the outside ambient air.
The question is, How fast will this take because of the condition of your radiator?
If it's clean & full flowing, then your coolants temperature will reduce & your engine will remain within it's working parameters.
If it's blocked internally with sediment then coolant won't flow & heat transfer will not occur so your engine will exceed it's working parameters & then overheat.

If the radiator fins are blocked externally with dirt, leaves, fluff or what ever, then the same senario will occur but you can at least see the problem with your own eyes & clean the fins so air can pass through freely & heat tranfer will occur more efficiently.

Nigel.

[haydn callow]

Gotta agree with all that.......
When I first got the latest Bongo it was (it seemed) running fine and all was well with the cooling....However the header tank was badly stained so I suspected that all may in fact NOT be 100%........I put a chemical flush in and gave it as good a flush as you can do with a hosepipe.....removing as many hoses as required and backflushing just about everything including the rad for 30 mins.......refilled and all seemed well......noticed after a week that the coolant was slightly discoloured so decided the radiator must have some "crud" in the bottom....removed the rad and it weighed a good Kg more than a exact replacement new one...

My conclusion....you will have a very hard job removing "crud" from the bottom of the rad....Bongo now runs 3 or 4 degrees cooler than before although temps were acceptable before changing the Rad.

[jaylee]

Thanks fer putting the time in to explain guys... This is a great thread, & it certainly highlights the importance of a clear flowing rad...!

So, then... Why did they stick a ruddy gert air con condenser in front of it??

[roofraisers]

Jaylee wrote:-

So, then... Why did they stick a ruddy gert air con condenser in front of it??

It's all about priority & how things work efficiently.

The air con. condensor works by cooling compressed refrigerant which has just come from a compressor as a hot high pressure gas.
It passes through the condenser & cools to a high pressure liqued.Heat has been removed to the surrounding air.
This high pressure liqued then passes through a very small hole into the evaporator.
Once in the evaporator the liqued pressure drops & it can now evaporate into a gas again.A liqued turns into a gas by attracting heat from the air around it.
This low pressure gas then returns to the compressor & the whole cycle begins again.

HEAT CAN ONLY BE TRANSFERRED TO A COOLER SUBSTANCE.(not shouting, just stating a bit point before continuing)

If you want your car interior at 10*C, then the low pressure air con gas has to be lower than this, to be able to absorb heat.
To be efficient the returning high pressure liqued needs to be as low a temperature as possible to be able to absorb as much Bongo interior excess heat as possible.

If the condenser was on the other side of the coolant radiator, on a hot day the minimum air temperature is going to be above 90*C (see previous post) after the air has cooled the engine coolant.This temperature is going to be unable to cool a high pressure air con. refigerant & so as the refigerant progresses through to the evaporator it isn't cold enough to be able to absorb any Bongo interior heat & the air con. would be ineffective.

With the condenser in front of the radiator, the ambient air temperature cools the air con. refigerant but the air temperature as it leaves the condenser is still less than 90*C and is therfore able to absorb heat from the coolant as it passes through the radiator.
This results in both systems losing excess heat to the air as efficiently as possible.
It would be great if the front of the Bongo was a bit taller or wider then both condenser & coolant radiator may be mounted side by side & could be cooled independantly, each with it own clean cool air source.

This may be a bit long winded but I hope it makes sence.

Nigel

[jaylee]

I does Nigel, thanks!

Sorry to come up with these Q's, it's just my enquiring mind seeing things like the gear box or the condenser & wonder what contributing factors they bring to the heat exchange table with the engine..?!!

I wasn't trying to suggest these units where doing a "tapeworm"... Probably explains why the fans need to kick in when the AC is on!

Nice one..