Overheat query

Technical questions and answers about the Mazda Bongo

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DaveH76
Junior Bongonaut
Posts: 23
Joined: Mon Jun 15, 2020 12:23 pm

Re: Overheat query

Post by DaveH76 » Sun Nov 08, 2020 3:25 pm

I have been out and started the van up with the thermistor plugged in again, and when the engine was running I unplugged the temperature sender unit which brought the radiator fans on full speed.

So, from this I am going to conclude that:

1 - the radiator fans for the cooling system are fine
2 - the scavenger fan cuts in before the radiator fans
3 - the reason the glow plug light was flashing yesterday when the scavenger fan cuts in was because there thermistor was unplugged.

When I next get a chance I will run it up again with the thermistor plugged in to confirm my second and third conclusions.
DaveH76
Junior Bongonaut
Posts: 23
Joined: Mon Jun 15, 2020 12:23 pm

Re: Overheat query

Post by DaveH76 » Mon Dec 14, 2020 10:58 pm

Thought I would update this as a point of reference for future searches, etc.

My presumptions below were incorrect. The reason the scavenger fan cuts in was because the engine bay thermistor was unplugged. Removing the thermistor from the centre panel and plugging it in to the loom meant the scavenger fan didn’t cut in when the engine was running on my drive.

Since my last post I have:
  • Drained the cooling system by draining the radiator, removing the bottom hose at the thermostat end, and removing the rear heater matrix pipes
  • Removed the thermostat, cut the core out, and refitted
  • Filled the cooling system with tap water and cooling system flush
  • Run the engine until the fans kicked in
  • Drained the system again and flushed through the rear heater matrix, back-flushed the rear matrix supply pipe so clean water came out of the rear matrix return pipe, flushed the front heater matrix, removed and flushed the radiator, back-flushed the engine, and flushed through the top and bottom hose runs
  • Replaced the water pump, thermostat (fitted a Mazda genuine) and rear heater matrix rubber pipes (felt a little ‘brittle’)
  • Filled the system with red anti-freeze and deionised water
I have disposed of over 50 litres of water so I reckon I have thoroughly flushed the system...!!

I have run the engine up until the cooling fans cut in and have gives it a few runs up the steep local hills and all seems to be fine. The thermostat is opening and the bottom hose is getting fairly warm (not anywhere near as hot as the top hose) but this is not giving me any cause for concern.

I have some dye to put into the cooling system which I will do tomorrow and then keep an eye on the level going forward, but I am fairly confident I had a blockage which resulted in air being pulled in via the header tank overflow.

Once again - thanks for all of your input on this. Much appreciated \:D/
Bob
Supreme Being
Posts: 15255
Joined: Wed Oct 17, 2007 12:54 pm
Location: North Somerset

Re: Overheat query

Post by Bob » Tue Dec 15, 2020 12:22 am

Well done, and a really useful update, thanks. 8)
rita
Supreme Being
Posts: 3284
Joined: Tue Sep 15, 2009 7:11 pm

Re: Overheat query

Post by rita » Tue Dec 15, 2020 12:21 pm

Did you renew the header tank pressure cap, good luck.
DaveH76
Junior Bongonaut
Posts: 23
Joined: Mon Jun 15, 2020 12:23 pm

Re: Overheat query

Post by DaveH76 » Tue Dec 15, 2020 1:51 pm

No I didn’t replace the pressure cap. It still seems ok but only time will tell!! And, if I am honest, I didn’t think to either!

The temperature gauge rises up to normal air quickly and pretty much stays there with no overpressure issues so I think the cap should be OK..... [-o<
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