Bongo Fury

Forget what you have and try to find out what you should have Danyboy. Buy borrow or perloin a copy of Four-Stroke Performance Tuning by A Graham Bell. The chapter on cooling explains why your heads go, its all down to the boiling point of water under pressure, and how pressure needs to be used on the outlet side of the head back to the rad.

Thanks for that Dandy and DannyBoy. I understand now. I hadnt considered the need to 'bleed' air past it when filling the coolant system and couldnt understand why air would be involved in normal operation - Duh

For a techiehead this has been a fascinating thread and there's been sooooooo much info exchanged it been a privilege to be part of and the various offshoot threads.

I know a bit about Bongos and vehicles in general but I'd never actually sat down and worked out how the Bongo cooling system worked.
There's been some great work going on here and I for one have learned from it.

Big thanks have to go to alphabetter, allans, demon, jamesnjane, vanmaneric, dannyboy, great pretender, hatdn, antique, grumpo, franco, veg ian, pete, mike, brora, harry et al for their inputs, I'm sure I've forgotten some, please don't be offended - lets hope we can get to the bottom of this one..........

Praise from the Big D is praise indeed. It is true though (and I wish more of todays over ambitious managers were 'big' enough to get their heads around this) that many heads in debate (sometimes heated - thats normal) and pulling for a common solution, and with a few 'elders' moderating it all, will always be better than the JFDI* style of management.

Mike

* Just F Do It (v popular with the corporate lawyers I worked with - they held the power and the cash, so everything they said MUST be right).

Hi, just to let you all know that i havent abandoned the quest, im back at work now in the navy so havent got as much spare time and ill be away till august soon so ill have to try and catch up as best i can when i can. still running with a holey stat so looking forward to a solution.

its been a pleasure using the forum on this topic with you guys, im positive you will crack it. (the problem that is not more heads!!!!)

best of luck

Hope this helps, although written primarily for race cars the cooling system is the same in race/road petrol/diesel. Although he talks about peak efficiency at 4 to 6000rpm he is relating to petrol engines, diesel peak efficience will be lower.

Also the thermostat is on the outlet of the head (return to radiator).


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If that didnt work, try this

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I understand whats being said there TGP but another theory of the thermostat on the return side is to alleviate the restriction of the highly pressurised, exceedingly hot coolant in the head and let it go to an external heat exchanger whether it be a radiator or hoses or whatever.
Retaining highly pressurised coolant at 125 + deg C in the head because the thermostat is causing back pressure can cause distortion and very overheated exhaust valves IMO.

Sorry Dandy, actually the opposite of what you are saying happens. The hottest part of the head is around the exhaust valves, water there can boil producing air pockets. The higher the pressure there the less chance of that happening. Flow,pressure and temperature (flow to return) need balancing. Low pressure in the head means lower boiling point, air bubbles, then localised overheating.

Ok, I'll go with that but I meant more the distortion/seize factor due to the high temperature being allowed........all good theories though

The water dosnt cause the high temperature, the head produces very high temps that need dissipating, hence the need for the pressure to be raised, and this needs the stat or a restrictor on the outlet of the head to create it, like a pressure cooker, this make sense?

Yeah i know the combustion process creates the temperature not the coolant - I'm just wondering about the chickens and egg senario as heat produces more pressure allowing the boiling point to be raised causing it to heat more if restricted by the stat - but I suppose the pressure cap release pressure will dictate that and blow off (causing coolant loss )

No Dandy, it isnt the rad cap controling the pressure in the head with the stat after the head it is the restriction that it creates that increases the pressure above what the rad cap can do. The higher the pressure,water stays water, let it boil, it cant cool. The higher the pressure the longer it stays water, doing its job. After the stat as the water speed has to increase to pass through it pressure reduces. Make sense?

Sorry to open this topic up again but this info may be important.

I removed my thermostat today, checked it was opening correctly in hot water and the carefully replaced it making absolutely sure it was positioned and located correctly in the thermostat housing.

I then carefully bled the cooling system.

Lo and behold for the very first time the bottom hose did not only get warm, it got hot. This shows that the thermostat had opened and the coolant was circulating.

Is this a first??

Is it possible that the thermostat can be assembled in such a way as to prevent it from opening? If so this could be the reason why so many Bongos are getting HOT.

I nearly put mine back in upside down, not having noted details when I removed the old one and because you are working blind when doing the job from on top (no - dont go there!!!). I suspect the housing may not have tightened up if I had, but something alerted me in time (to my surprise, but cant remember what, maybe it didnt seat well or w.h.y.).