Overheating MN Triton

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Overheating MN Triton

Postby V-Man on Wed Apr 20, 2011 8:33 pm

I've recently been having some issues with my MN Triton and I'm desperately trying to figure out what might be causing it to intermittently overheat.

The ute is stock as a rock, no mods and has almost 48,000K's on the clock.

About four weeks ago I was headed off to work, towing approx 1.5 Tonne of trailer and equipment behind me as I usually do every day. The outside temp was about 7 degrees. After driving about 40K's sitting on 100 - 110 I pull off the highway and into traffic. While stopped at some lights I hear the radiator spewing coolant from the overflow and the temp gauge almost into the red. Pulled over and called roadside assist, who topped up coolant and told me to head to the nearest Mitsubishi dealer as the Mitsubishi roadside assist doesn't cover towing of trailers. A little over a week later I get my car back with a new thermostat fitted. I was shown the old one, which had obvious signs of wear (rub/scrape marks on one side) I was told that this is where it had been sticking and that this was the cause of my problems.

Two days after the new thermostat was installed I sat at a set of lights and watched as the temp gauge rose up about one bar and then drop back to normal just as quick, for the next four weeks I kept a close eye on the temp gauge just in case, but it never seemed to move once the engine had warmed up.

2500K's and four weeks later I do the same trip as the first one but headed towards home, outside air temp of approx 20 degrees. I pull up at home, start reversing the trailer back to park it and and smell coolant, I check the temp gauge and see it has risen almost to the red again. After allowing the car to cool, I take it to my local dealer (different to the first one), this time the thermostat is checked and appears to work correctly, the radiator was removed and given to the local Natrad guy, who was unable to find any blockages or other issues with it, the thermo fan is also apparently working correctly. The car is road tested and sat in the car yard running for over an hour with no issues. As they cannot replicate the fault I was given the car back this afternoon.

Both dealers (and I spoke to the mechanics as well as the service managers) have said that there doesn't appear to be any problems with the head or head gasket. So if it's not the head, the radiator isn't blocked, the thermostat has been replaced and the replacement seems to be working correctly and the thermo fan is working correctly what else could it be?

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Overheating MN Triton

Postby mattz on Wed Apr 20, 2011 8:54 pm

Is it an auto?
I have heard of them over heating whilst towing.
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Re: Overheating MN Triton

Postby gregned on Wed Apr 20, 2011 10:34 pm

My best guess an airlock or cavitation or pressure drop where localised boiling is happening. MRT had some write-up about waterpumps in their subi running more eficiently at slower speeds as they had coolant boiling issues.The
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Re: Overheating MN Triton

Postby V-Man on Thu Apr 21, 2011 6:12 pm

Thanks guys,

Mattz - it's a manual, luckily. I was given an ML auto to drive by one of the dealers while they had mine and I reckon I'd be broke if I had to keep paying for the fuel it was using.

gregned - The first dealer I went to thought that it may have been an airlock. The coolant was drained as part of the 45k service that they did at the same time they replaced the thermostat, would this not remove an airlock?

Took it to the parent in laws place this arvo and crawled around their paddocks in the mud in low first, everything stayed cool.

I may go and get some firewood over the next couple of days so I'll tow a couple of tonne behind and see if that causes it to happen again. Not that I want it to overheat, I just want to find out what's causing it and get it fixed as I'm reluctant to go bush, or take the family anywhere too far from home just in case.
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Re: Overheating MN Triton

Postby Longranger1 on Thu Apr 21, 2011 7:30 pm

Have you ever cleaned your intercooler out? Not part of the cooling system, but if it is full of oil (not using a catch can) then the charge air temperature will go up fairly dramatically. This could possibly stress your cooling system, especially if you are towing or carrying heavy loads.
I wouldn't have thought it would affect cooling that much but if you have gone through the whole cooling system and it checks out ok then it might be worth a shot.
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Re: Overheating MN Triton

Postby Tony on Thu Apr 21, 2011 7:57 pm

Longranger1 wrote:Have you ever cleaned your intercooler out? Not part of the cooling system, but if it is full of oil (not using a catch can) then the charge air temperature will go up fairly dramatically. This could possibly stress your cooling system, especially if you are towing or carrying heavy loads.
I wouldn't have thought it would affect cooling that much but if you have gone through the whole cooling system and it checks out ok then it might be worth a shot.


Good point, although in my findings the coolant temp has not been effected by either high intake temps nor rising EGTS.
The 2.5 has a very efficient cooling system thankfully in my case. :roll:

I'm also thinking along the lines of an airlock or cavitation in the pump area.
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Re: Overheating MN Triton

Postby Longranger1 on Mon Apr 25, 2011 5:54 am

Another thing which may have been overlooked is the radiator cap - did they pressure test it?

If the radiator cap isn't holding it's design pressure, then you could have the problems you describe as localised hotspots in the block will boil due to lower boiling temperature of the coolant.

The higher the pressurization of the coolant the higher the boiling temperature becomes.

In hot weather with the a/c on mine runs at about 94 degrees C.
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Re: Overheating MN Triton

Postby V-Man on Wed Apr 27, 2011 9:28 pm

Longranger1 - Dealer 1 supposedly did a pressure test, so this should be OK.

So far so good though, nearly a week back from the last Dealer and no overheating so far. I just hope it stays that way.

The worrying part is that all they have done is pull the radiator apart, checked a few things and put it all back together again. Nothing has actually been fixed, so I'm sure it's just a matter of time before it happens again.

At least I will be armed with some extra ideas to bounce off the Mitsu mechanic.
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Re: Overheating MN Triton

Postby brown on Sat Apr 30, 2011 2:47 pm

I also have a MN GLX triton that is intermitantly over heating. Most of the time is at night below 8 - 15 degrees & with no load on or trailer. A dealer told me they have had problems with thermo fans. I found last night, that mine is over heating with spot lights switched on. The gauge goes right to the top in about 15 sec's from middle( Normal) while going up hill, or under load (accelerating)on a flat road, drops off very slowly, going down hill, but turn the spot lights off, and the gauge will drop to normal in about 30 sec's up hill or down hill. I also noticed 2 nights ago while testing, that the thermo fan was not roaring when I pulled up and reved it while gauge at max, but last night it was working. I have not had it over heat with 900kg on back of ute plus 2 tonne trailer on during the day in hot weather, so I'm also at loss of what is wrong, but thinking is there some electrical interferance with engine management, or is it something else. The last time it was doing it regularly, I got the 30000 km service done, & it hasn't happened again until now at 37500kms.
A local dealer told me they will check for carbon build, because they believe the other dealer I took it to for the 30000 km service cleaned the inlet manifolds. Sorry I can't give you any answers, but maybe someone will work something out from the problems I'm having to.
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Re: Overheating MN Triton

Postby V-Man on Tue May 03, 2011 1:57 pm

Sorry to hear your having similar issues brown, but I'm also glad to hear that it's not just my ute that mysteriously overheats.

Dealer number two thought it may have been my thermo fan, (2 plus weeks delivery time from Japan) but reckons he checked it and apparently it works fine. I've lifted the bonnet and seen the thing working but now that I think about it, I honesty can't recall the last time I actually heard the fan working hard while driving, and this used to be quite common with both the ML and MN.

Just wondering if you may be onto something with your electrical interference theory. I was actually wondering about this myself, as I've been having heaps of issues with my electric trailer brake controls since they were installed on the MN. I'm not in any way mechanically minded, but just wondering if it's possible that a bad install (my brake controller, your driving lights) could adversely affect the thermo fan or water pump somehow?

Just wondering if it's possible as the overheating only seems to happen when I'm towing.
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Re: Overheating MN Triton

Postby Cowboy Dave on Tue May 03, 2011 6:24 pm

V-Man wrote:
Just wondering if it's possible as the overheating only seems to happen when I'm towing.


If it was a really bad trailer brake install maybe you're dragging a trailer with its brakes locked on? That'd overheat you after a while I would have thought. This only occurs to me as I had a trailer lock up on me over the Easter weekend. i didn't notice while in the mud because it slid along happily but when I hit the tar it slowed me down a bit. :oops:
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Re: Overheating MN Triton

Postby Longranger1 on Tue May 03, 2011 6:44 pm

The thermo fan and the water pump have no electrical bits to worry about. Have you checked the actual temperature using a scanguage or similar? I checked the the block temp with a scanguage and a Fluke thermo gun (which concurred). I'd say if is only overheating while towing, then the issue is somewhere in the cooling system and that has been overlooked.
Another possibility is tuning. Are you running a chip? It is possible that altered injection timing is causing overheating.
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Re: Overheating MN Triton

Postby brown on Wed May 04, 2011 9:00 am

V-Man, I have possibly solved my problem with temp gauge rising. I have moved the earth for the spotlights from a spot on the body below the battery, near the main earth wire, and now its not overheating. This was suggested by a local auto electrician, who said they get all sorts of strange things happening with these new elctronic controlled injection vehicles, if any accessories are earthed to the body. I would presume the electrical interferance was influencing the fuel injection or timing, to cause it to overheat with a slight increase in load. I have not let it lose any coolant yet, but I have had to get out of the cab to stop my leg getting burnt from the exhaust temp coming through the floor. The floor mats must have just about melted.

I would not rule out the thermostatic fan, but I would certainly be looking a your electronic brake controllers earthing.

The earth I had on the spotlights was not dirty or poorly connected, but was near the main earth wire off the battery.
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Re: Overheating MN Triton

Postby Honky on Wed May 04, 2011 10:35 am

Had a small car where the electrical fan was disconnetted accidently.
Only overheated when caught in traffic as cooling was good enough when moving without the fan.

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Re: Overheating MN Triton

Postby brown on Wed May 04, 2011 2:15 pm

Forgot to mention that I put all the accessory earth wires on to the battery terminal, which has stopped the overheating.
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Re: Overheating MN Triton

Postby hvac guy on Wed May 04, 2011 6:15 pm

have they checked the fan clutch?
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Re: Overheating MN Triton

Postby V-Man on Wed Jul 27, 2011 5:33 pm

Alright, time for an update......... as a lot has happened in the past couple of weeks.

Two and a half weeks ago I stopped to make a quick phone call and the cabin fogged up, after the call I started driving but the windows had fogged up a bit as it was freezing cold and I was drenched. No biggie, I turned the heater to high and turned on the A/C to defog the cab.

I drove for a few Km's and the heater was blowing freezing cold air. Something's not right here I thought, another Km or so down the road the heater kicks in and its bloody sweltering hot. I look at the temp gauge and it's almost in the red, I turn the heater off and the temp gauge drops :o So I head to the nearest dealer, only to be told that it's my fault because I haven't been topping up the coolant properly and that is why the car is overheating.

Off I drive again with my topped up radiator, this time I make it home and the temp gauge is back in the red and coolant is pissing out of the overflow. I drive back to the dealer, throw the keys at the service manager, who looked somewhat surprised to see me and said "I told you before that it's f****d, now fix my f****n car".

After checking the thermostat, the water pump and pulling out the radiator again, the mechanics still had no idea what was going on. They called the Mitsu techs, who advised that they (lucky for all you other MN owners) have only had a handful overheat, and the problem has been rectified by replacing the thermostat.

As this was not the problem, the head was removed and inspected. No apparent problem there, but on inspecting the block, my problem was found - at last.

There must have been an issue at the time the block was cast, which was not picked up by Mitsu quality control. In between pistons three and four was a groove that was very visible to the naked eye. This was allowing exhaust gas into the cooling system and coolant into the piston. The exhaust gas was apparently boiling the coolant which made it overheat and spew out the overflow.

The solution, (without any arguments from Mitsubishi)I finally picked her up today with a brand new motor. I'm so damn happy that Mitsubishi actually stood by their warranty.

To celebrate I took her out and bought her a shiny new set of tyres and put her through the car wash.
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Re: Overheating MN Triton

Postby fridgie on Wed Jul 27, 2011 5:47 pm

Glad to hear you got it sorted mate!! Others have had a lot less luck than that ;)
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Re: Overheating MN Triton

Postby gregned on Wed Jul 27, 2011 8:27 pm

Glad that your problem is sorted
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Re: Overheating MN Triton

Postby norto on Thu Jul 28, 2011 6:40 am

There is an MN down here thats getting a new
motor because it's overheating and they can't
find the problem.
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Re: Overheating MN Triton

Postby ML-VR08 on Mon Feb 13, 2012 9:17 am

OK i know mine isnt a MN but i was towing a boat loaded around 2.6t and my truck was around the 2.65t full fuel then add on 4 blokes around 375kgs (so near 3t). I was thinking to GCM was around the 5.6t. Was towing with O/D OFF sitting on around 2500rpm and the temp guage got upto the last white line before the red. This only happened on the long hills pyro was sitting on 380degrees, with boost spiking to 24psi 8-) - does this seem normal temp for the loads/weight we were carrying/towing? I was pretty happy with the truck, used 90L for 530kms!!! very good economy... thats running FLD 2 custom tune 2 (chipit chip) and boost mod!!!
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Re: Overheating MN Triton

Postby Custom Offroad on Mon Feb 13, 2012 1:16 pm

ML-VR08 wrote:OK i know mine isnt a MN but i was towing a boat loaded around 2.6t and my truck was around the 2.65t full fuel then add on 4 blokes around 375kgs (so near 3t). I was thinking to GCM was around the 5.6t. Was towing with O/D OFF sitting on around 2500rpm and the temp guage got upto the last white line before the red. This only happened on the long hills pyro was sitting on 380degrees, with boost spiking to 24psi 8-) - does this seem normal temp for the loads/weight we were carrying/towing? I was pretty happy with the truck, used 90L for 530kms!!! very good economy... thats running FLD 2 custom tune 2 (chipit chip) and boost mod!!!



That seems like unbelievable figures mate :shock: :shock: I have a manual ML and towing my 2t boat with gear the piro runs up around 550-600c on long hills!! Boost is running around 19psi. That fuel economy is ridiculious I am very :mrgreen: Mine gets around 450km to a tank :(
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Re: Overheating MN Triton

Postby ML-VR08 on Mon Feb 13, 2012 1:39 pm

I have always had a very good fuel returns in my truck, even running the bigger tyres and full barwork and heavy steel tray. My dad has the 630F (haines sig) and i get rougly the same figure towing it. When the boost is sitting at around 11psi flat road, the pyro did get to around the 440-460 deg. but never got over 460. not sure why, and as i said was very happy with the fuel figures, seeing as i was very close to 5.6t loaded up!

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Re: Overheating MN Triton

Postby ML-VR08 on Mon Feb 13, 2012 1:40 pm

sorry for the hijack aswel, mods if you would like to move my post feel free - maybe call it

1770 trip - or something??? :? :oops:
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Re: Overheating MN Triton

Postby MN GLXR on Mon Aug 06, 2012 4:50 pm

I have the same problem! I was driving my MN auto up to the snow fields today and the outside temp was -3 deg. I had the heater on full and I noticed the temp gauge slowly climbing. It then suddenly rose all the way up to 100% just as we arrived.

On the return 30km drive the gauge did not move off stone cold until I was near home. It then suddenly jumped to normal reading (about 40%) before creeping up to 90% in the driveway.

I popped the bonnet and everything seemed fine. The overflow coolant was cool and the radiator cap felt warm but not hot. Does that mean the temps are ok?

I wonder if this is dodgy thermostat or something else? Never had any issues with temp until today.

I have a week at snow and this is day 1 so I will watch it closely.

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