Alternative theories to overheating

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Alternative theories to overheating

Postby Gnomeo on Fri May 13, 2022 9:30 pm

Hi guys,

Familiar with the overheating threads but after some possible alternative theories.

- 2015 MN manual
- Safari snorkel fitted with overflow relocated
- 146,000km, serviced every 15,000km with intermittent in between minor services
- heater core and head gasket replaced around 60,000km along with new radiator cap under warranty due to no heat from heater.

Today I was driving back from Sydney towing our camper - not a drama at all under load etc… and temps only crept up to what I’ve experienced before while up hills etc. I have an ultra gauge which triggers a coolant alarm at 98C so I can back off if needed. No previous signs of overheating.

Got home an unhitched, drove to shops unladen. On way home, Ultragauge overheat alarm triggers as I’m pulling up to some red lights, and it increases when stopped, getting to 100C. Temps decrease but are super erratic when driving from then on.

Got home and the expansion tank is full with 1-2 bubbles visible every 60 sec or so from overflow tube while at idle. The overflow vent has/had small amounts of coolant coming out of it.

I cracked the radiator cap when cool (not cold) and instantly massive amounts of bubbles flowed into overflow tank (presumably from the radiator cap). Radiator neck was not full, and I couldn’t see fluid down to the bottom of the elbow.

I started engine and couldn’t see any coolant flow but there was a vapour coming out (hard to tell if hot/boiling fluid vapour but no distinct smell) and no bubbles anywhere to indicate combustion gases.

The top radiator hose and both heater hoses were hot, but the bottom hose was only just warm but I couldn’t feel pressure in it. I idled it for a while and there wasn’t much flow that I could see (as the fluid in the neck was barely visible) but revs were only at idle as I was alone. No bubbles (that I could see whilst alone) in the overflow or radiator neck. I took it for a short test drive and the temp was all over the joint as if it was air locked or had a bubble in it somewhere. During the drive the heater (at full ball) lost heat for a short time before it came back, making me think there was a airlock/bubble too.

I returned home, topped off the radiator with demineralised water (roughly 600ml, noting the overflow tank was still almost full) for testing and idled for a while with/without heater on and at 2k rpm before taking it for another test drive. During the drive (14min under varying loads up to 100km/h) and the temps appeared fine again. Lower hose/elbow off the bottom of radiator was very cool to the touch while top hose was as hot as you’d expect. The overflow bottle was is still just as full as it was before.

Now, I’m dreading it might be the worst case but I’m also wondering whether it could be a bum water pump, thermostat, blockage or something else.

This has come out of the blue and no other dramas at all apart from a burst intercooler hose a while back

Making this worse is I’m towing the van (1.4T) onto fraser in July, so not great timing..

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Re: Alternative theories to overheating

Postby MNtritonRobbie on Sat May 14, 2022 5:04 am

Hi mate,

My advice is to take it straight to your Mitsubishi dealer. I had the same overheating issue on my 2012 MN earlier this year. Spent a thousand or so replacing radiator and thermostat with my own mechanic only to have the issue arise a month or so later. After reading this forum I rang my Mitsubishi dealer and booked it in explaining the issue I was having and said I would like a pressure test done. Dropped it off to them and 3 days later got a call saying I was getting a new long motor free of charge. It was a great experience in regards to customer service but this may differ between dealers. I wouldn’t hesitate if you have a trip in July as it took about 4 weeks to get all the parts complete the replacement. Maybe ask them on pricing a few consumables, I got a new heavy duty clutch while the motor was out supplied and fitted for just over a thousand dollars. Good luck mate.
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Re: Alternative theories to overheating

Postby NowForThe5th on Sat May 14, 2022 5:20 pm

Yes, take it straight to your dealer.

If work is so terrific, why do they have to pay us to do it?
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Re: Alternative theories to overheating

Postby bigjobs on Sun May 15, 2022 8:24 am

Hey mate,

Doesn't sound good, unfortunately.
Go to Mitsubishi and ask for a combustion leak test.
Same symptoms as my original, temps were all over the shop and eventually failed at over 120°c. Also monitoring it with an Ultragauge.

My 2014 MN had a long motor replacement in 2016 which I've since put 100k on, without any real dramas.

My experience has been that the replacement also still drops a small amount of coolant from the overflow bottle (safari eBay copy) whenever it's working a bit harder, mostly in low range and soft sand eg. bypass tracks on Fraser and the temps get up a bit into the high 90's.
My temps are stable and has been tested ok by Mitsubishi at Springwood.

I'd still probably go to Fraser but I'd get cover from one of the towing places that offer towing/recovery packages for peace mind :-)

I'm keeping the MN until it dies I reckon, it's a shitbox but it gets the job done.
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