Cooling system

The Great Pretender · Post by **The Great Pretender** » Mon Mar 24, 2008 11:18 pm

Hi guys n girls the cooling system is something I have been thinking about for a while and am looking for answers.

Im going to do some experimenting with the system so any info will be appreciated.
The system seems to be a compromise and could create problems that possibly lead to head problems.

Does anyone know why the stat is on the return?
As it only opens at 82c is anyone monitoring the max temp at the outlet from the head?
As the return to the stat is apparently always cool does the stat open?
Is anyone monitoring the pressure in the system?
Feel free to answer or add thoughts or other concerns.

flippa · Post by **flippa** » Tue Mar 25, 2008 12:42 am

are you saying the stat is in the wrong place tgp? could/would it be of better use on tother side?...one question id like answering (pretty basic) flow direction /what way does the coolant travel when filling from the tank?....might help me understand the filling bleeding process

The Great Pretender · Post by **The Great Pretender** » Tue Mar 25, 2008 1:01 am

flippa wrote:are you saying the stat is in the wrong place tgp?

No, im asking is it, im thinking it is.
could/would it be of better use on tother side?

Everything I know tells me it should be there

...one question id like answering (pretty basic) flow direction /what way does the coolant travel when filling from the tank?....might help me understand the filling bleeding process

Cold water is heavier than hot so it will fall, if the only way into the system was through the bottom hose how would it get there as the stat is closed? It has to get there eventually through the degassing tank and heating pipework.

Bleeding in my opinion is the Bongo's headache and the root of the problems

dandywarhol · Post by **dandywarhol** » Tue Mar 25, 2008 2:37 am

I think using the incorrect bleeding procedure is a cause but I think infrequent coolant changes/cleaning causing silt buildup in the matrices and radiator are the root cause.

I can't find an answer to why it's on the return but my own opinion is that wax stats are notoriously fickle when operating at high temperatures. In to pre 80s most engines stats opened at 82 on the outlet side. Then it changed to 88/92 as engines ran hotter to be more fuel efficient.

A waxstat will invariably fail CLOSED - so it's curtains for the head gasket/head if the system overheats. I changed far more stats on cars when they opened at the higher range than the older cars.

Sooooo.........I think they've designed the stat to operate under less stressful conditions on the relatively cool return side. I first saw it on an early 80s VW/Audi Passat engine.

It's only recently that manufacturers have designed/fitted ECU controlled servo operated thermostat valves to allow a finer control of the cooling system.

I believe that the myriad of pipes, hoses tank and matrices are sufficient to keep the system cool as long as they're not blocked. The radiator is not operating in this circuit as the stat is closed most of the time. When the stat is closed it allows coolant to flow in a bypass system which includes the heater matrices, expansion/degass tank, oil cooler, turbo cooler.

When greater demands are put on the cooling system - low speed up hills, in traffic etc. the thermostat fully opens due to a combination of heat tranfer from the lower radiator tank/hose AND heat transfer from above at the bypass system and the thermostat housing/stat itself.

This then closes off the bypass system and the majority of the cooling now takes place through the radiator because the heat can transfer by convection currents. The water pump's main purpose is to lift the cool, dense coolant from the bottom of the radiator up to the water jackets - it doesn't "pump" it around the engine. The coolant is circulated around the engine by convection currents lifting it up and out the head by the DRIVER'S side to the top of the radiator and the tank.

I haven't yet measured the running pressure in the system but I expect it to be around 2/3 psi. This allows the coolant to circulate at around 103/104 deg.C The cooling fans cuts in at 108 deg. which makes the pressure around 5psi. This is a perfectly acceptable pressure for the system to deal with. The pressure cap on the tank is rated at around 16.5 psi before it's valve opens and lets the excessive pressure blow off to atmosphere. So, whenever a faulty system blows it's coolant out of the cap there's something seriously wrong because the coolant temperature is around 123 deg.C at that stage

Airlocks are a serious problem because they inhibit circulation and create "hotspots" in the water jackets in the engine. But they only appear when the coolant has been lost first.

The problems arise IMO when the system calls upon the radiator to help cool excessive heat. If the radiator core is partially choked then it can't do it's job and overheating occurs.

Ralph · Post by **Ralph** » Tue Mar 25, 2008 11:00 am

If the diagram is correct they are using the stat to control
the cold side ie return side of the system, but as the stat is
upside down in the housing the cartridge thing that works it
is in the hot flow from the head via the pipe from the tree
were the bleed pipe for those lucky enough to have one is
connected that is why if you don't get all the air out at that
point the stat does not open and it cooks it's self, once you
get hot flow at that point by bleeding, the stat opens and you
get full flow that pushes water round fast enough to allow any
trapped air to escape via the header tank, hence burping
your Bongo.
But if I am right in that why when the stat opens does the
instant rush of cold water not cause the stat to slam shut,
no not happy with my own explanation cant look today but
will tomorrow see if I can work out whats going on at least
to my own satisfaction, usually water leaves the engine at
the hottest point ie the head controlled by the stat and
returners cooler via the cylinder block or water pump.

My take on it any way but open to other views.

dipstick · Post by **dipstick** » Tue Mar 25, 2008 11:22 am

I read somewhere that drilling a small hole in the thermostat allows a small amount of coolant to circulate around all of the circuit all of the time so you do not get overheating.

Let us know how you go on if you try it out.

dandywarhol · Post by **dandywarhol** » Tue Mar 25, 2008 11:47 am

I haven't seen a Bongo stat Ralph but it looks from the manual that it fits in with the wax element in the return side of the system and the valve at the top is the bypass control. I don't think it can physically fit in the wrong way - Mike and others will be able to reply to that one.

The stat is opened IMO by a combination of heat (?) from the returning coolant AND heat transfer from above i.e. the bypass coolant/housing temperature.

Dipstick, An extra hole is only going to guise a problem unsolved. But it will do as you say.

I hope we're not going to piss the majority of forum readers off as this is going over old ground from almost a year ago which lasted for 21 pages and resulted in (at least

) one forum member having a sex change

http://www.igmaynard.co.uk/bongo/forum/ ... ht=cooling

I don't have the drawing skills as the original artist but I've shaded in red what I think is happening. I don't believe the direction changes as in note 1. It circulates in an anticlock flow from the head at the driver's side.

scanner · Post by **scanner** » Tue Mar 25, 2008 12:13 pm

Ralph wrote: But if I am right in that why when the stat opens does the
instant rush of cold water not cause the stat to slam shut,
no not happy with my own explanation cant look today but
will tomorrow see if I can work out whats going on at least
to my own satisfaction, usually water leaves the engine at
the hottest point ie the head controlled by the stat and
returners cooler via the cylinder block or water pump.

My take on it any way but open to other views.

Because it will gradually "feather" it's opening to allow just enough hot water through to maintain adequate flow and thus cooling, whilst still putting full heat through the heater circuits.

Too cold it closes up, too hot it opens again etc etc, until just right.
If it didn't do that your heater would keep going on and off all the time as the flow fluctuated.

The radiator is only there to dump any surplus heat left after you have defrosted the screen and warmed your tootsies.

____________________________________________________________

Thought

Could this be a reason for overheating problems.

Bongos used in cold conditions may rarely (especially if used for lots of short trips) use their radiators, when they suddenly change to running in conditions where the heaters aren't needed, the radiator can't cope with the demand put on it as it's partially or wholly silted up.

Just a theory shoot it down if you like.

dandywarhol · Post by **dandywarhol** » Tue Mar 25, 2008 12:29 pm

Makes sense!

Maybe we should do a poll of radiator problems by originating area. Mine's from Osaka in the south - no problems (yet

)

mikeonb4c · Post by **mikeonb4c** » Tue Mar 25, 2008 1:47 pm

[quote="scannerThought

Could this be a reason for overheating problems.

Bongos used in cold conditions may rarely (especially if used for lots of short trips) use their radiators, when they suddenly change to running in conditions where the heaters aren't needed, the radiator can't cope with the demand put on it as it's partially or wholly silted up.

Just a theory shoot it down if you like.[/quote]

That is a really interesting thought. I find it hard to believe that heating the car can dissipate engine heat to the point where the rad. is not needed. But as I think about it, a large and poorly insulated interior space coupled with extreme cold and front and rear heater rads could provide a lot of cooling to an engine already sitting in a low ambient temperature. Mind you, you'd think they would have hor summers in between the cold winters, when the main radiator would get some 'exercise'.

I have to admit I can't follow the finer points of the coolant system/how does it work debate so leave it to others!

MountainGoat · Post by **MountainGoat** » Tue Mar 25, 2008 1:49 pm

My 1998 SGL5 Bongo is from Nagoya in the south of Japan. No problems with it yet but I have had a set of Flipa's hoses fitted at Wheelquick as a precaution.

haydn callow · Post by **haydn callow** » Tue Mar 25, 2008 1:49 pm

I hope we're not going to piss the majority of forum readers off as this is going over old ground from almost a year ago which lasted for 21 pages and resulted in (at least

) one forum member having a sex change

Very good.

vanvliet · Post by **vanvliet** » Tue Mar 25, 2008 2:01 pm

http://www.pvrdirect.co.uk/productinfo. ... tref=VS602

last_tuesday · Post by **last_tuesday** » Tue Mar 25, 2008 2:23 pm

vanvliet wrote:http://www.pvrdirect.co.uk/productinfo. ... tref=VS602

That's for cissies. Do it properly, use an isotope and a Geiger counter

mikeonb4c · Post by **mikeonb4c** » Tue Mar 25, 2008 3:05 pm

haydn callow wrote:I hope we're not going to piss the majority of forum readers off as this is going over old ground from almost a year ago which lasted for 21 pages and resulted in (at least ) one forum member having a sex change

Very good.

Understand your sentiments HC, my brain can't take any more input on this one unless someone can lure the Mazda designer out of retirement and fund him on a UK lecture tour - I'd be there

Cooling system

Cooling system

Thermostat