Cooling system

[Grahame at work]

Brora when you changed out the sensor did you loose much coolant and have to refill and bleed etc. ?
Also did it come out easily?

regards Grahame

[brorabongo]

It's from my Brother-in-laws bongo. He changed the switch himself, and got a little wet doing it, so he told me, I did ask at the time how much water was lost, and he thought he did not lose much.......but how much is much?

He had already started to fill the system before I arrived to give him a hand ( ) with the bleeding. I just hope we bleed it right. It's not a job, I would say I am totally confident in doing.

We did get a few burps, using a funnel in the bleed pipe, and rising and lowering it, whilst reving etc. So I told him to keep an eye on the level in the tank, plus an eye on the temperature gauge etc.

[francophile1947]

I'm no expert and, unfortunately cannot do your drawings on the computer, but I think both Aethelric's and alphabetter's diagrams are wrong.
Aethelric's show all sources flowing toward the thermostat - this surely cannot be right cos' where does the water go when the flows meet? I think alphabetter's diagram around the thermostat is more logical as it allows a continuous flow.
Both diagrams have the water flowing through the heater system in opposite directions for the front and rear heaters - how can this happen in a pumped system without causing turbulence where the contraflows meet. I believe it is more logical that the water flows in an anticlockwise direction through the rear heater and continues, in the same direction, through the front heater, thus forming a continuous flow round the circuit from the bottom of the hose from the "header/expansion" tank and back to it - at least this means that the water flows, in the same direction throughout the system.
Hope this makes sense to everyone.
Be gentle with me cos' I really don't know the answer , but it does seem more logical that all the water flows in one direction.

Hi John
The diagram does not show the output of the thermostat, which is into the engine. Somewhere in there, the coolant meets the pump and gets pumped out of the top hose. I think the heater return flow joins up in the engine as well.
Two flows meeting are no problem, its just the opposite of one flow splitting.
We are all guessing BTW, apart from Grahame who is taking real measurements

Dave

Thanks Dave, I never thought about it going into the engine
I still think it makes more sense if the entire heater system flows in one direction though - must make for a better flow

[alphabetter]

Hi John
The diagram does not show the output of the thermostat, which is into the engine. Somewhere in there, the coolant meets the pump and gets pumped out of the top hose. I think the heater return flow joins up in the engine as well.
Two flows meeting are no problem, its just the opposite of one flow splitting.
We are all guessing BTW, apart from Grahame who is taking real measurements

Dave

Exactly.

This is another thing that would be really useful. If someone who has taken the termostat housing apart could show us how the various pipes (including the hidden one to the engine) are connected with the termostat closed and open that would provide more evidence.

[Aethelric]

Here's a way to test the fan switch. It seems to work on mine. (Mind you I'm not sure that mine is right )
When the engine in warmed up after a run. Switch it off. Open the bonnet and wait a minute or so. Now switch on the ignition, but not the engine. The fan should start. This is because the heat of the engine has got to the radiator switch. The fan should keep running because, as the pump is not running, its doing a pretty ineffectual job of cooling the engine. Now start the engine. The coolant will now circulate, cool the sensor down, and the fan should cut off after 10-30 seconds. Make sure you have the A/C off as those fans wil mask the sound of the radiator fan. I'm not saying this is a rigorous test, but it gives confidence.

Dave

[dandywarhol]

Sounds like yours is running a bit too hot if that's happening Dave - especially in this cool ambient temperature. I did the pressure checks on mine the other day in a 20 degC workshop and it didn't do as yours does.

Grahame.

When you remove the sensor - block off the hole somehow, put an ohmeter over it's connections and imerse it in a pan of room temp water and heat the water up.
The readings should be:
20 deg.C - 2300 - 2600 ohms
80 deg - 290 - 340 ohms

[Bongo.Baz.tard]

Sorry if i missed something.
Sort of making sense of this , barely .
What i would like to know is should the expansion tank be hot?

[Aethelric]

Sounds like yours is running a bit too hot if that's happening Dave - especially in this cool ambient temperature. I did the pressure checks on mine the other day in a 20 degC workshop and it didn't do as yours does.

Grahame.

When you remove the sensor - block off the hole somehow, put an ohmeter over it's connections and imerse it in a pan of room temp water and heat the water up.
The readings should be:
20 deg.C - 2300 - 2600 ohms
80 deg - 290 - 340 ohms

Hi Dandy. I was worried about that, but I thought it made sense. How does this arguement fit:-
A properly warmed up engine should run at the same temperature, winter or summer. That is what the thermostat is meant to control. It should be lower than the temperature which switches on the fan, otherwise the fan would be on all the time. However it should not me MUCH lower than this temperature or the temperature variation from normal, to fan assisted would be excessive.
Putting figures in, - the thermostat keeps the engine at a temperature which is arrived at with coolant water ay 82C. If the coolant gets to (say) 90C the thermostat is wide open, cooling is not enough, so the fan kicks in.
The engine works with the internal surfaces of barrels, pistons and valves exhauset manifold etc at much higher temperatures than 100C. When the engine is switched off, this heat dissipates into the cooling water, now not moving. (There must be an engine design criteria for any water cooled engine to have enough coolant mass in the engine to keep it below boiling in this period.)
So the coolant tempertature in the head will rise to its absolute maximum after switching off a hot engine. It would be better if the coolant kept moving but all it has now is a little convection, which will stop if the thermostat closes - and the thermostat is affected by the rapidly cooling water in the bottom hose so will cut of quickly.
You can see the same effect on digital projectors, switch it off and the fan keeps running for a minute or so to cool it down.
SO I think its a valid test, but if it only works on mine then the logic must be wrong

[haydn callow]

I have invested in a digital laser thermometer. Using this I reckon I can determin the direction of flow along any pipe in a few seconds. By simply "scanning" the beam along a pipe the temp will either go higher/lower. The direction of flow will be from hot to cool.
If I can do any readings that will help this topic let me know.

[Aethelric]

I have invested in a digital laser thermometer. Using this I reckon I can determin the direction of flow along any pipe in a few seconds. By simply "scanning" the beam along a pipe the temp will either go higher/lower. The direction of flow will be from hot to cool.
If I can do any readings that will help this topic let me know.

That sounds great Haydn. The "other" pipe leading to the thermostat (the one from the heater supply) would be interesting. I think this is the main input for coolant to the engine until the thermostat opens when it starts to come from bottom hose. It should also be hotter than the bottom hose before the stat opens fully.

Dave

[dandywarhol]

What you say is right Dave - the heat soak will activate the fans but as the fans are connected through the "ignition" switch then they won't work if it's off. Some cars do have the fans connected into the main battery supply so they can come on when the engine/vehicle has stopped.

What I'm looking into now is why the thermoswitch for the fans aren't just an on/off switch. the figures I posted earlier show there's a circuit contact at both 20 and 80 deg.C I would have expected an open circuit at 20 deg.

I've got access to a laser guided digital thermometer thingy haydn - I'll borrow it from the college for the weekend.
I used it to give Dave Mason some info for his alarm perameters - it seems pretty accurate.

[haydn callow]

I reckon the flow from the rear heater supply to the top of the stat housing is from the stat housing down to the metal rear heater T junction. ( could be wrong) but I was getting a 5 C differance on the rubber connecting pipe 4" along from the stat housing and 4" up from the T. Hotter nearer the stat.
Also 70 C on the top of the stat and 18 C on the bottom.
I can confirm that coolant flows from the head via the top hose to the top of rad, then out of top of rad to the header tank. What I'm not sure of is if coolant is also flowing into the header tank via the smaller bottom hose or leaving via this hose to the heaters.
The laser thermometer seems to work well. (£20 from China)
I noticed that the rad fans were coming on/off for no apparent reason whilst the engine was nowhere near warmed up. Always been the same. Not worried. Bongo runs well and we tow a C'van.

[Grahame at work]

Dandy

The fan sensor is very similar (or the same) as the sensor for the dash gauge. It is a temperature dependant resistor, this is why I will be connecting a volt meter to it and monitor the value while travelling.

There must be a logical reason for its position in the head (or is it the block?) I just can't think what it is.

Haydn

Your Bongo sounds similar to mine in fan operation.

I can feel a Poll coming on - just can't think of the questions yet

I will be re-positioning my temperature sensors and investigating the fan sensor at the weekend .
[I haven't told Valerie yet so I've got some negotiating to do ]

Regards Grahame

[Aethelric]

What you say is right Dave - the heat soak will activate the fans but as the fans are connected through the "ignition" switch then they won't work if it's off. Some cars do have the fans connected into the main battery supply so they can come on when the engine/vehicle has stopped.

What I'm looking into now is why the thermoswitch for the fans aren't just an on/off switch. the figures I posted earlier show there's a circuit contact at both 20 and 80 deg.C I would have expected an open circuit at 20 deg.

I've got access to a laser guided digital thermometer thingy haydn - I'll borrow it from the college for the weekend.
I used it to give Dave Mason some info for his alarm perameters - it seems pretty accurate.

Just a thought
They may use a temperature dependent resistor to introduce a bit of hysteresis. Relays have built in hysteresis in that the pick up voltage (where they close) is always higher than the drop off voltage (where they open). So with temperature dependent resistor in series with the relay its possible to have a bigger temperature range between between coming on an going off than you would get with thermal switch. I don't know why they would want this though

This would preclude having the relay off the main battery as even with the fan off, there would be battery drain. I think the bongo needs the pump operating for cooling though, and keeping the fan on after the engine has stopped would have minimal effect.

For the test BTW I did say switch on the ignition, but not the engine

Dave

[Aethelric]

I reckon the flow from the rear heater supply to the top of the stat housing is from the stat housing down to the metal rear heater T junction. ( could be wrong) but I was getting a 5 C differance on the rubber connecting pipe 4" along from the stat housing and 4" up from the T. Hotter nearer the stat.
Also 70 C on the top of the stat and 18 C on the bottom.
I can confirm that coolant flows from the head via the top hose to the top of rad, then out of top of rad to the header tank. What I'm not sure of is if coolant is also flowing into the header tank via the smaller bottom hose or leaving via this hose to the heaters.
The laser thermometer seems to work well. (£20 from China)
I noticed that the rad fans were coming on/off for no apparent reason whilst the engine was nowhere near warmed up. Always been the same. Not worried. Bongo runs well and we tow a C'van.

Hi Haydn, there are only two pipes to the header tank(I think) so if its flowing in one, it must be going out the other.
Hmm - trying to get my head around that flow at the stat. If hot water is coming out of the stat, it can only be coming from the engine. That implies its supplementing the the hot water from the header tank. Can't see the logic in that. Anyone any ideas?

Dave