Cooling system

[dandywarhol]

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

Is the temp gauge sensor not a single wire thermoswitch earthed in the head?

[dandywarhol]

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

Maybe I'm misinterpreting your question Dave but the stat will flow hot coolant through the bypass valve at the opposite end to the main thermostat valve. It will also allow heat to transfer down the body of the stat to the main valve .

Thanks Bongobits

[Aethelric]

Hi Andy / Haydn

I thought the flow was as shown here



But that assumes a flow into the stat bypass from the heaters. Haydn's measurements suggest the flow is the other way from the stat.

Dave

[Grahame at work]

Dandy,

The sensor for the dash gauge is indeed earthed at the sensor but it is a temperature dependant resistance - there is only one wire coming from it.

The sensor further back in the head is also a temperature dependant resistance. The difference is that this sensor is part of the control system, feeding the coolant temperature to the ECU. This sensor has two wires both going back to the ECU (nowhere near any relays). The temperature reading is used to control the cooling fans, the scavenger fan, the glow plug operation and the idle revs The ECU wants to know when the coolant goes over 20C, over 60C and over 108C.

So if this fails lots of things could go wrong.

But Brora didn't report poor starting on his brothers Bongo did he? (or was it an inlaw Brora - sorry)
By the way I dont suppose you tried to check for any fault codes when you were checking it out did you? According to the book you should have had service code 09 for a disconnected sensor.

I have got this from the schematics and the workshop manual but I note several errors in the workshop manual regards the ECU functionallity so it may be "almost true".


Regarding the flow schematic - I think it is improtant to note that the hose that goes from/to the header/expansion tank to/from the heaters is smaller diameter than both the other hose connected to the tank and the metal pipe that it is connected to near the heaters.
I'm working on the pipework trying to come up with a better drawing (no offense Alphabetter) but its not easy

Bed time again

Regards Grahame

[The Great Pretender]

Im a beliver in the KISS system. What goes where is in the main irrelivent, the top of the radiator the return pipe is hot I think we all agree. What you are all missing is what is happening at the bottom of the radiator, that will provide the answer.
Where is my tin hat.

[dandywarhol]

OK got you Grahame - the rear sensor also signals to the ECU to lock up the torque convertor when it feels like it..........

[Aethelric]

Im a beliver in the KISS system. What goes where is in the main irrelivent, the top of the radiator the return pipe is hot I think we all agree. What you are all missing is what is happening at the bottom of the radiator, that will provide the answer.
Where is my tin hat.

The top of the radiator is hot because there is a flow of hot coolant into it from the top hose. Some of it comes straight out again to the header tank.
Some of it travels down through the radiator and out of the bottom hose. When the stat is fully open, most of the coolant will go this way. The bottom hose will be hot, but not too hot as the radiator will have cooled it.

Now, as regards the stat, I think it is supplied with hot water from the header tank as well as cool water from the bottom hose. When the hot water from the header tank reaches 82C the stat opens and becomes a sort of mixer tap, feeding the engine with a mixture of hot water from the header tank and cooler water from the radiator, but maintaining an average temperature of 82C.

So, the bottom of the radiator will remain cool until the top of the radiator (or the header tank) has reached 82C. There may be a low volume bleed through the stat, which is why the bottom of the rad gets warmish quite quickly, or it may be that the the water at the top, which is what feeds the stat via the header tank reaches 82C quite quickly.

Thats my take on it. It seems logical, good engineering and fits the measurements taken by the folk here (with the execption of Haydn's measure of direction flow from the heater T piece to the stat, which he did say could be wrong)

Dave

[haydn callow]

Why carn't coolant be flowing into the header tank via BOTH hoses ???

[dandywarhol]

I think that makes sense and I've been saying that for a wee while now.
So..............if the bottom of the radiator is sludged up then the systems not operating properly WHEN IT'S REQUIRED MOST.
The van will run fine using the top tank and assocciated piping/matrices until a demand is made on it like long accents/towing/low gear, low speed work..........the stat opens fully at 95 deg, the coolant can't circulate past the sludge and the engine overheats.
Blow, blow, crackety crack - the games a bogey..................

Alan

[dandywarhol]

Why carn't coolant be flowing into the header tank via BOTH hoses ???

I think it flows back to the thermostat bypass by return. As TGP and others are saying it isn't really an expansion tank (although the coolant level does raise when hot allowing expansion) it is an integral part of a flow system in an anticlock direction if you like when the stat isn't allowing the radiator to be part of the circuit.

Still to find out why the coolant level doesn't fall relative to the amount removed when TGP removed the stat

[brorabongo]

But Brora didn't report poor starting on his brothers Bongo did he? (or was it an inlaw Brora - sorry)
By the way I dont suppose you tried to check for any fault codes when you were checking it out did you? According to the book you should have had service code 09 for a disconnected sensor.

No problems starting on the Brother-in-law's bongo. I did not think to check for a fault code, how do you do it anyway?
There were no warning lights that stayed on, to give us an idea that something was wrong. I just knew that the radiator fans should'nt be on constantly, so investigated it.

[Aethelric]

Why carn't coolant be flowing into the header tank via BOTH hoses ???

I'm not sure what you are getting at Haydn. If there was flow in via both hoses, how would it get out?

[Aethelric]

I think that makes sense and I've been saying that for a wee while now.
So..............if the bottom of the radiator is sludged up then the systems not operating properly WHEN IT'S REQUIRED MOST.
The van will run fine using the top tank and assocciated piping/matrices until a demand is made on it like long accents/towing/low gear, low speed work..........the stat opens fully at 95 deg, the coolant can't circulate past the sludge and the engine overheats.
Blow, blow, crackety crack - the games a bogey..................

Alan

Yes, and it will work in the same way with a jammed closed thermostat - there is still a path via the header tank.
So, does the stat start to open at 82C, and is then fully open at 95C?

A problem though - I've just noticed that the only way for cooled water from the heaters to get into the engine is via another inlet on the block! Any ideas how the coolant flows inside the engine?

Dave

[haydn callow]

why should we assume that coolant has to flow "through" the expansion tank. why can coolant not flow in from 2 directions when hot and just settle there "finding it's own level.
Don't really know what I'm suggesting. I don't see any reason why coolant cannot arruive at the tank from two directions

[The Great Pretender]

Listen very carefully I will say this only once.

The bottom hose from the rad is the key to how the system works and anyone can check it out. You dont need fancy equipment just your hand and a little common sense.

Drove from Wigan to Burnley today 35ml on the motorway at 60 to 70 mph, as soon as I left the motorway I stopped and felt the bottom hose, it was COLD.

Now it dosn't take Einstien to understand that as the Bongo isn't overheating the cooling system must be working.
Ok so as the rad is hot at the bottom as your little pinkies should find out, logic says the coolant is flowing elsewhere.
So if the coolant isn't returning to the engine through the bottom hose where is it flowing. Any light bulbs going on yet?

Yep you have got it, it is flowing through the degassing tank.