Cooling system

The Great Pretender · Post by **The Great Pretender** » Fri Mar 28, 2008 11:30 pm

Ok for all you doubting Thomas's out there, here are a couple of pics.
The engine is up to working temp.

2000rpm around the speed the engine at around town.

Now the intreting bit.

Now do you believe.

Post by **Simon Jones** » Sat Mar 29, 2008 12:12 am

TGP - I'm interested in what you're using to monitor the pressure - its the kind of thing that may assist in my expansion tank woes. Is that the pukka thing that fits in place of the radiator/expansion tank cap?

Quite a big difference in pressure between the two extremes - does the pressure increase/reduce inline with the change in engine speed, or is there a delay?

The Great Pretender · Post by **The Great Pretender** » Sat Mar 29, 2008 12:19 am

Simon Jones wrote:TGP - I'm interested in what you're using to monitor the pressure - its the kind of thing that may assist in my expansion tank woes. Is that the pukka thing that fits in place of the radiator/expansion tank cap?

Quite a big difference in pressure between the two extremes - does the pressure increase/reduce inline with the change in engine speed, or is there a delay?

You really need to read the thread, I made this to fit on the OUTLET of the head. It virtually tracks the rpm.

Post by **Simon Jones** » Sat Mar 29, 2008 12:44 am

Thanks - I've been reading that thread too, but didn't spot the bit about that connection.

The Great Pretender · Post by **The Great Pretender** » Sat Mar 29, 2008 12:52 am

Did you also realise it is now on the outlet not the inlet and the pressure is in the head not the tank?

Aethelric · Post by **Aethelric** » Sat Mar 29, 2008 10:21 am

Have I got this right then?

The pump is generating pressure against a closed thermostat. The outlet of the thermostat feeds the bottom hose and because it is closed the water is stationary in the bottom hose and thats why its usually cold.

Water is flowing in the top hose, but its coming OUT of the radiator. So it must be coming into the radiator via the header tank. The radiator gets hot all over, so the path between the two top pipes must feed the water around the radiator.

Is it coming into the headertank presumably from the heater and aircon circuits? So the pump must be feeding these, before the thermostat. Its a long path from the thermostat to the header tank and radiator, and the pressure relief valves and that is why the pressure is high here.

So before the thermostat opens, the water that runs around the radiator is WARM as it has already passed through the heating and aircon system. When the thermostat opens it is HOT as it comes straight from the engine.

I'm new to this, and trying to get my head round it. If I'm talking bollicks let me know.

Dave

haydn callow · Post by **haydn callow** » Sat Mar 29, 2008 12:18 pm

Coolant flows out of the thermostat into the cylinder head then out of the cyl head into the rad via the top hose.
Coolant enters the Stat from below via the bottom hose.
The thought is that the stat open/closing and dumping cool coolant into the hot cyl head could be causing problems over a period of time.
Not sure I go along with that as most cylinder head/gasket problems arise after a overheating episode.

Aethelric · Post by **Aethelric** » Sat Mar 29, 2008 1:21 pm

haydn callow wrote:Coolant flows out of the thermostat into the cylinder head then out of the cyl head into the rad via the top hose.
Coolant enters the Stat from below via the bottom hose.
The thought is that the stat open/closing and dumping cool coolant into the hot cyl head could be causing problems over a period of time.
Not sure I go along with that as most cylinder head/gasket problems arise after a overheating episode.

I believe that TGPs monitoring of the pressure was at the point in between the head and the thermostat (was it??) and the pressure got very high. The bottom hose connects to the radiator and ultimately to the header tank both with pressure relief that must limit the pressure to less than TGP measured. So if the thermostat were to open, it would flow from the cylinder head to the bottom hose through the thermostat.

Dave

haydn callow · Post by **haydn callow** » Sat Mar 29, 2008 1:29 pm

TGP has moved the stat to the top hose where it leaves the cyl head. This is where he is reading the pressure.
The coolant is heated by the head....leaves the head via the top hose....enters the top of the rad....cools and drops to the bottom of the rad......then along the bottom hose to the head again....passing through the stat when open (not in TGP's case) co's he has resited the stat

Aethelric · Post by **Aethelric** » Sat Mar 29, 2008 1:38 pm

haydn callow wrote:TGP has moved the stat to the top hose where it leaves the cyl head. This is where he is reading the pressure.
The coolant is heated by the head....leaves the head via the top hose....enters the top of the rad....cools and drops to the bottom of the rad......then along the bottom hose to the head again....passing through the stat when open (not in TGP's case) co's he has resited the stat

Ahh I see!, But if the stat has been moved its not a standard bongo any more. Back to the drawing board.

haydn callow · Post by **haydn callow** » Sat Mar 29, 2008 2:02 pm

Correct.. but the argument for moving the stat could well be valid if it prevents "cold" coolant being dumped into a boiling hot head and causing stress.
This is the point that I am not convinced about.
I am going to put a temp sensor into the standard bongo stat housing and try and work out exactly whats going on in there.
In the meantime I have sourced a "made up" stat in-line housing that comes with a 82C stat for around £28. I will also experiment with that later. It can be fitted in any hose over 32mm Dia.

The Great Pretender · Post by **The Great Pretender** » Sat Mar 29, 2008 2:27 pm

I realise some of this can be difficult to get your head around so let me restate.
The main reason for moving the stat to the outlet was to increase the pressure INSIDE THE HEAD you cannot get that with the stat in the inlet.
By increasing the pressure the boiling point is raised allowing more heat to be transfered from the head.
The hottest part of the head is around the exhaust ports and the coolant in the water jacket in that area can boil causing gas pockets that then as not in contact with coolant causes localised stress.

haydn callow · Post by **haydn callow** » Sat Mar 29, 2008 2:41 pm

Right...think I'm getting there.
I understand the bit about raising the pressure in the head to raise the boiling point to prevent coolant boiling and causing gas pockets/local stress.
But by doing this are you not also allowing the head to heat up more, by the same amount of degrees as as the higher coolant temp? Is the one benifit not being offset by this.

lizard · Post by **lizard** » Sat Mar 29, 2008 3:17 pm

With all this tech stuff going on I thought I would ask a more simple question.

When a Bongo is working well, the temp gauge(mason) shows 12:30: to 01:00, even when the Bongo is pushing 60/70 up hill then is waiting at lights with the mason is set to just below 4, the alarm just beeps for a tad,(thought I would get technical) then stops.

Every thing seems rosy, what can go wrong, except for mechnical breakdown of the cooling system, pump belts, hoses, etc, I ask my self.

What happens in hot weather, is there a design fault with the system, can a perfectly working enging suddenly for no mechanical reason over heat and pop ( another technical term) the cyl head.

Questions Questions Questions.

The Great Pretender · Post by **The Great Pretender** » Sat Mar 29, 2008 4:08 pm

haydn callow wrote:Right...think I'm getting there.
I understand the bit about raising the pressure in the head to raise the boiling point to prevent coolant boiling and causing gas pockets/local stress.
But by doing this are you not also allowing the head to heat up more, by the same amount of degrees as as the higher coolant temp? Is the one benifit not being offset by this.

Are you confusing pressure and temp? The higher pressure allows better heat transfer. The pressure is a result of the restriction the stat causes not by higher temperature.