Cooling system diagram

[widdowson2008]

It looks like someone's going to have to factsheet this lot before it all gets lost/pruned/forgotten

Slow down Kirsty - first things first - the fact sheet will be created. Trust me on this one. and thanks for your help

[mikexgough]

Here's my thoughts on the workings of the cooling system. I somehow picked up from previous threads that the thermostat "pointy end" faced up the way - now that its been confirmed otherwise I can make sense of whats happening. If this has already been said in previous threads then apologies.

On "conventional" cooling systems with the 'stat at the outlet from the head the cold coolant heats up in the water jackets and convects upwards towards the thermostat. It does't get past the 'stat at this stage but circulates by a bypass system back round to the waterpump and further convects until it is hot enough to open the 'stat. The 'stat valve is opened by the wax contained in the "bulb" of the thermostat expanding through heat and it opens the valve. There's always coolant at either side of the 'stat (assuming no airlocks) - its the heat transfer by convection thats taking place through the coolant which keeps the cycle going.
The hot coolant, at around 90 degrees, then transfers to the radiator and depending whether it is a crossflow or vertical flow type, travels through the radiator which, as the name implies, radates the heat to the atmosphere. Because modern vehicles have the lower tank on the radiator at a position lower than the engine block, the waterpump then lifts the cooled, dense coolant back up into the engine. Then the coolant recircluation cycles starts all over again.

Now for the Bongo system........................

I think it was TGP who said the waterpump is actually "pumping" coolant around the system on the Bongo, I contradicted him.................and he is right! The Bongo system, with the 'stat in the return to the engine setup does rely on the pump “pumping” the coolant around the engine, whereas the “conventional” setup has the pump “lifting” the coolant from the lower radiator tank to the engine block.

Righto……………I think this is what happens.

The cold coolant is warmed by the cylinders, the waterpump assists the heat travel process by taking coolant from the bypass system above the thermostat (the ‘stat is closed at this point but the disc shaped valve (seen in Allans excellent pics mentioned by Kirsty), is open allowing the bypass system to be open. The coolant heats up, convection currents lift the coolant to the highest outlet in the head, to the pipe seen under the driver’s seat and directly forward to the top of the radiator. As the hot coolant mixes with the cold coolant in the radiator its easiest path for heat transfer is to go up to the expansion/auxiliary tank (because heat rises and the radiator coolant isn’t allowed to circulate at this point due to the closed thermostat not allowing circulation). This hot coolant circulates through the expansion/aux. tank and carries on to the heater circuits and ends back in the previously mentioned bypass system above the thermostat. The waterpump then takes the coolant back from the bypass into the engine block. From memory, there are no external coolant hoses on the pump – it just takes coolant from A to B internally.

The coolant in this system, including the block/head/hoses/metal pipes/radiator top tank/heater matrices/turbo cooling system and various metal pipes will be staying at a fairly uniform temperature. Fluctuations will occur (probably as previously mentioned the reason the gauge is damped) but the volume of coolant and expanse of piping does its job in keeping the system at a safe working temperature, just below thermostat opening temperature. There will a few “glitches” when stopped in traffic/hill climbing/hot ambient temperatures when the coolant temperature will be high enough to heat the “bulb” on the ‘stat enough to open the thermostat. And as the coloured diagrams that Mike Gough posted of the Elise/MG system shows, there will be a mix of bypass coolant and some colder coolant allowed to enter the system from the radiator, via the now partially opened thermostat. This would explain the temperature fluctuations recorded on the TM2 gauges.

If the conditions then really demand extra cooling then the ‘stat will fully open, the bypass system will close off by the disc shaped valve and the entire cooling system will constist of the block/head/outlet hose under the driver’s seat/radiator/lower radiator tank/thermostat/expansion, aux.tank/heaters et al until things cool off enough to partially close the ‘stat again and the system reverts back to the former setup. The closed off bypass system then allows the warm coolant from the radiator bottom tank to go past the thermostat directly into the engine block. Allan’s photos show this.

If this the case, then vehicles used in cold climates in Japan or Europe might rarely have the complete system functioning in full flow and possibly why the radiators in these vehicle choke up.

Thanks for reopening this one widdowson, I think it’s becoming clearer through time……………………….and nobody has fallen out …………………..yet!

Yep............ agree with that and explained as clear as I could, although perhaps if a "dummies guide" type of Fact sheet is produced it could also point out the weaknesses of the system and why bleeding is done in a particular way and also benefits of any monitoring add ons..... Just a thought

[haydn callow]

Makes sense to me......I always advocated that the "stat hardly ever opens on a Bongo" and took a lot of flack for my thoughts...Then..after reading everything else and particularly after making the gauge work properly and observing the fluctuations I came round to the thinking that the stat was opening/closeing all the while...
I now have come across a digital temp gauge which can cope with 3 sensor inputs...I intend to get hold of one and put the 3 sensors in differant positions around the system....
Anyone got thoughts on the best places to get useful info ??
Falling out over topics is pointless and unproductive....even if you think the opposit to the majority..
When I first got the Bongo ...having misunderstood what a very competant Bongo expert said.....I was convinced the Flow of coolant was reverse in a Bongo...i.e. from the engine DOWN the bottom hose and UP through the Rad.
After a long confusing thread, I think it was Dandy and one other who PM'd me and put me right...No fuss or bother untill I apologised within the topic....then I got a load of abuse via PM.

Thankfully that attitude seems to have stopped and now everyone can put their views forward right or wrong...

Well done everyone for your efforts so far on this topic....nice one

[francophile1947]

That makes sense to me
Like Haydn, I always thought that the stat rarely opened and the main cooling was done by the heater radiators (via the bypass system). I have never had my bottom hose hot when I've checked it, even after fairly long journeys. However, I am sure it gets hot sometimes, because I have never overheated - it's just that I can't get out to check it when I'm doing 70mph
Keep up the good work

[widdowson2008]

Stage 1 - Gathering preliminary information and opinions and producing preliminary schematics
I have produced 3 schematics:
1 - Thermostat fully CLOSED
2 - Thermostat fully OPEN
3 - Thermostat midway in sort of a 'hunting' mode
this is complete almost - I still have info coming in via pm's but I think I have enough to procede to

Stage 2 - Kirsty suggested that I run the schematics past Mike, Dandy and Doone for their comments.
For this I need their email addresses. I have Mikes already. If Dandy and Doone could let me have theirs I would appreciate it.
When I get their response(s), and have made the necessary modifications to the schematics, I will re-submit to get confirmation/agreement

Stage 3 - Produce a 'dummies' guide to the cooling system, incorporating all info from this post where relevant.

Job done - exit Steve

As I have information of a more technical nature still coming in, I will pass this on to the relevant members so that an 'Advanced' guide can be produced. But this will be toooooooooooooooo technical for me

To all those who helped on this project, thank you

[missfixit70]

[quote="mikexgoughYep............ agree with that and explained as clear as I could, although perhaps if a "dummies guide" type of Fact sheet is produced it could also point out the weaknesses of the system and why bleeding is done in a particular way and also benefits of any monitoring add ons..... Just a thought[/quote]

That's exactly what's needed but that's a lot of info for someone to put together, brave person that takes it on

[mikexgough]

I also had a theory that the system was controlled in someway and with the progressive nature of the thermostat in this type of system it would be.
I have noticed this since fitting a Mason alarm (I had thought the gauge would be undamped and just raise to normal temperature and stay there much like a normal system and only drop when cold or raise when overheating occurs)

How wrong I was, the needle sits happy at Dave Mason's 55% in normal running then raising to 70% in traffic queues for example but when the traffic moves even for a short while say a few hundred yards (like on the A14 ) the needle drops back happily to 55% again..... without any cooling fans "kicking" in.

So my thoughts are at this time the coolant is allowed to rise in temperature and then the thermostat opens more to allow coolant to be introduced from the Radiator, then the water pump circulates the mixed coolant and the temperature then returns to the usual reading of 55%.. and I would then assume the thermostat would part close if needed....if that makes sense...only when the cooling system reaches extreme temperatures do the fans "kick" in......
Mine don't run very often and mostly after a short stop for fuel and they are fired up by heat soak, they spin for about 30 secs and the cooling system takes over the cooling process.

In essence since the start of the thread I feel that the Thermostat could be a or the weak link in the system if as we think that it progressively opens and closes are the engine requires.....if it fails to open/close.....problems occur...

I have thought about a gauge for in the coolant system......BUT where would be the best place to locate any sensors/probes? and how would this be measurable? especially with the fluctuations in temperature that occur.
If such a device could be made/calibrated then it would have to be "bullet proof" and ultra reliable in operational conditions but be simple too..
These people do a lot of cooling system bit's n bobs and might be a help http://www.revotec.com/index.asp but what do others think?

Personally now, I would incorporate and recommend a Thermostat change when the coolant is changed followed by the full bleed process and all should be well in the world, for the nominal cost of a Thermostat it could prevent a lot of hassle.
Can I also thank all the contributors to the thread for their intelligent debate and analytical way we have discussed this topic.... well done folks...

[widdowson2008]

Yep............ agree with that and explained as clear as I could, although perhaps if a "dummies guide" type of Fact sheet is produced it could also point out the weaknesses of the system and why bleeding is done in a particular way and also benefits of any monitoring add ons..... Just a thought

That's exactly what's needed but that's a lot of info for someone to put together, brave person that takes it on

If thats what it takes to understand the cooling system, then so be it.

[missfixit70]

Personally now, I would incorporate and recommend a Thermostat change when the coolant is changed followed by the full bleed process and all should be well in the world, for the nominal cost of a Thermostat it could prevent a lot of hassle.
Can I also thank all the contributors to the thread for their intelligent debate and analytical way we have discussed this topic.... well done folks...

Fully agree, as I have been advocating for a while Also a full & thorough flush (easier with the stat out) to elimniate the possibility of mixing incompatible coolant, especially in those parts of the system not usually opened up. This mixing can result in jelly like blockages.

[widdowson2008]

This started life as a small project to get a simple cooling system diagram.
Its turned into a bloody obsession and I'm thoroughly enjoying it

[haydn callow]

Dandy said.......The coolant in this system, including the block/head/hoses/metal pipes/radiator top tank/heater matrices/turbo cooling system and various metal pipes will be staying at a fairly uniform temperature. Fluctuations will occur (probably as previously mentioned the reason the gauge is damped) but the volume of coolant and expanse of piping does its job in keeping the system at a safe working temperature, just below thermostat opening temperature. There will a few “glitches” when stopped in traffic/hill climbing/hot ambient temperatures when the coolant temperature will be high enough to heat the “bulb” on the ‘stat enough to open the thermostat. And as the coloured diagrams that Mike Gough posted of the Elise/MG system shows, there will be a mix of bypass coolant and some colder coolant allowed to enter the system from the radiator, via the now partially opened thermostat. This would explain the temperature fluctuations recorded on the TM2 gauges.

If the conditions then really demand extra cooling then the ‘stat will fully open, the bypass system will close off by the disc shaped valve and the entire cooling system will constist of the block/head/outlet hose under the driver’s seat/radiator/lower radiator tank/thermostat/expansion, aux.tank/heaters et al until things cool off enough to partially close the ‘stat again and the system reverts back to the former setup. The closed off bypass system then allows the warm coolant from the radiator bottom tank to go past the thermostat directly into the engine block. Allan’s photos show this.


Having just spent a hour with a Pan of water on the stove and a Thermostat and Stat housing......I think the above is a "spot on" description of exactly what goes on....

Even better..I understand it...

I have always made a point of "forceing" my bottom hose hot every now and again......Would I be right is saying that a Stats default mode is OPEN in the case of failure ??

[missfixit70]

Nope, closed, that's why the overheats happen, it just doesn't open.

[mikexgough]

Dandy said.......The coolant in this system, including the block/head/hoses/metal pipes/radiator top tank/heater matrices/turbo cooling system and various metal pipes will be staying at a fairly uniform temperature. Fluctuations will occur (probably as previously mentioned the reason the gauge is damped) but the volume of coolant and expanse of piping does its job in keeping the system at a safe working temperature, just below thermostat opening temperature. There will a few “glitches” when stopped in traffic/hill climbing/hot ambient temperatures when the coolant temperature will be high enough to heat the “bulb” on the ‘stat enough to open the thermostat. And as the coloured diagrams that Mike Gough posted of the Elise/MG system shows, there will be a mix of bypass coolant and some colder coolant allowed to enter the system from the radiator, via the now partially opened thermostat. This would explain the temperature fluctuations recorded on the TM2 gauges.

If the conditions then really demand extra cooling then the ‘stat will fully open, the bypass system will close off by the disc shaped valve and the entire cooling system will constist of the block/head/outlet hose under the driver’s seat/radiator/lower radiator tank/thermostat/expansion, aux.tank/heaters et al until things cool off enough to partially close the ‘stat again and the system reverts back to the former setup. The closed off bypass system then allows the warm coolant from the radiator bottom tank to go past the thermostat directly into the engine block. Allan’s photos show this.


Having just spent a hour with a Pan of water on the stove and a Thermostat and Stat housing......I think the above is a "spot on" description of exactly what goes on....

Even better..I understand it...

I have always made a point of "forceing" my bottom hose hot every now and again......Would I be right is saying that a Stats default mode is OPEN in the case of failure ??

As kirsty says........closed..... causing overheating....

Now as the thermostat will be working in a progressive way i.e part or full open it will no doubt be the weak link in the system.... so a the message Change Thermostat should be reinforced in any of the fact sheets IMHO and Kirsty is a staunch advocate of that thing too.

Now how a "bullet proof" simple temp gauge can be produced with all the fluctuations of engine temperature as well as the airflow temperatures like this mornings 4c to last weeks 12c......who knows? as how would it be measured without causing panic to the driver?
mmm lots of mulling over there.....

Also to add to the mix..... how often(bearing in mind the "How It Works" above) should the cooling fans need to cut in?......
Not often I would think (as well as my experience on my Bongo) with the way the system uses the heater matrices for cooling in the early part of the warm up as well as when at fully operating temperature........

maybe another topic for a constructive debate on the back of this highly intelligent and informative thread.....well done to all who have and are taking part......

[Doone]

Just for clarity, can I ask if you mean the radiator fans or the scavenger fan?

[mikexgough]

Radiator.....