Mitsubishi Outlander Auto Trans Cooler

Submitted: Tuesday, Jan 04, 2022 at 16:57
ThreadID: 143048 Views:4500 Replies:6 FollowUps:10
This Thread has been Archived

Having recently purchased a camper trailer and being excited to hit the road, I am wondering if there is a specific weight when one should install a transmission cooler.

The gross weight of the camper trailer is a few kg under 700kg being towed by a 2020 Mitsubishi Outlander petrol.

Any advice is appreciated, thanks.
Back Expand Un-Read 0 Moderator

Reply By: tonysmc - Tuesday, Jan 04, 2022 at 18:26

Tuesday, Jan 04, 2022 at 18:26
While 700kg is very light and shouldn't pose any problems, I wouldn't hesitate to install a transmission cooler anyway. I have put them on my last 2 auto cars and now wouldn't be without a tranny cooler. Another good addition to have something like a Scangauge to keep an eye on the trans temp, if your car is a late enough model to do this.
AnswerID: 638999

Follow Up By: Frank P (NSW) - Tuesday, Jan 04, 2022 at 21:28

Tuesday, Jan 04, 2022 at 21:28
Absolutely what he said.

Lifetime Member
My Profile  My Blog  My Position  Send Message

FollowupID: 917855

Reply By: RMD - Tuesday, Jan 04, 2022 at 20:16

Tuesday, Jan 04, 2022 at 20:16
Like Tony, above, I would fit one to an auto vehicle. Just one time towing and hot day with tail wind can change the overheating situation dramatically. Remember all the heat generated by the torque converter action in doing work on the fluid heats it well beyond the boiling point of water. That is why the cooler part of the radiator is used to cool the auto fluid, ie used as a heat sink. Make sure the cooler if fitted is in the HOT line exiting the auto so the maximum exchange rate can happen through a large temp differential. A fan assist can also be fitted if temps are not controlled. Try uphill on a hot day will high air temps and the towing load is far greater than on the flat. The auto will get hot and possibly engine enter limp mode to save the auto and or the engine. Just a few realistic reasons why you would!
AnswerID: 639001

Reply By: Athol W1 - Wednesday, Jan 05, 2022 at 10:17

Wednesday, Jan 05, 2022 at 10:17
I would, and do, fit an additional transmission cooler to my vehicles as the first modification that I do after purchase. The biggest killer of auto transmissions (and engines) is heat, and you only have to get behind a slow moving vehicle on a long hill that causes the transmission convertor clutch to unlock in ANY gear and the transmission temp (and engine temp) can and will go through the roof.

Whilst there are various arguments as to which line the cooler should be fitted to the fitment of an additional transmission cooler to either line will remove heat load from the entire cooling system.

Fitment to the hot line as preferred by some only means that the oil that leaves the radiator has been reheated before returning to the transmission. (that is the one from the transmission, this is not always the hot line to the touch as the heat exchanger in the radiator often HEATS the transmission oil, and some vehicles can increase the oil flow to reduce the engine temp, i.e. they are prepared to sacrifice the transmission to save the engine instead of fitting sufficient radiator capacity for all occasions) Others prefer the return line as the temp is being reduced to less than the temp of the lower radiator tank. ANY reduction in the heat load of the entire system will be of benefit to the entire system.

I prefer the fitment to be in the return line, as I was taught you can not overcool transmission oil.

Hope this helps.
AnswerID: 639002

Follow Up By: RMD - Wednesday, Jan 05, 2022 at 12:16

Wednesday, Jan 05, 2022 at 12:16
Athol and Jay
I know there is varied ways to fit a cooler. Some now have control valves of line flow.
If the auto is working hard then the engine is developing high heat output too, near rad capacity to dissipate, little spare ability. The fluid leaving the auto, arguably the hottest pipe, can be delivering 130C or more heat load to a nearly fully heat loaded engine cooling system, and therefore be driving coolant temp higher than the radiator ability can handle. We all expect it to cool no matter what, don't we? The Rad coolant at near maximum efficiency cannot accept high auto fluid heat loading as well without becoming overloaded in thermal dissipation capacity.
So, if the cooler is in the Hottest "exit" line, the elevated fluid temp has the maximum heat difference and ability to dissipate the most heat into the passing airflow and therefore the fluid has less ability to overheat the radiator which is already near MAX.
If the Hottest line is being delivered directly to the near Maxed out radiator, then engine coolant temp will elevate even more. When you use a heater at home and you are hot, do we turn it up hotter?

If the radiator is working normally, then it is far cooler where the coolant is drawn to enter the engine to cool it and provides a reserve of cooling ability, a good situation to be in, this can handle the lesser amount of auto fluid heat because the auto fluid has already had it's engine and auto killing temp dropped lower.

Cooler in the return line means, quite simply, if Heat Maxed auto fluid, delivered directly to the radiator can make the Maxed or near Maxed rad system work harder still, you are very near limp mode at the best. "Always work to have a reserve" Just because it hasn't failed ,"yet", doesn't mean the component/system life will be a longtime. And people wonder why their engine system cannot cope uphill, towing, with a tail wind on a hot day. Slow down, change down, make engine rotate fast enough and less heat load so it can handle it better.

Just before Christmas, my SIL used his Hilux to do quite heavy towing, and it got HOT and fried the auto. No cooler fitted. It is costly! Now has cooler and fan and temp switch.

Cooler in hot line, = max heat to air before auto, engine as normal, if rad bottom relatively cool as it should be then return line not too hot. rad able to handle some excess heat.

Cooler in Return line, = max heat to maxed rad, not in there for long and so some temp returns to cooler which isn't much different to air and because the heat dissipation differential is far lower, heat removal from the whole system is less. Auto runs hotter.

If you run a modern auto too cool, many will not select higher ranges of ratios and clutch slippage can burn clutches in auto if allowed to happen. My Corolla WILL NOT select lock up UNTIL the fluid has warmed to save the lockup clutch. Perhaps the factory tested it first.
FollowupID: 917859

Follow Up By: Athol W1 - Wednesday, Jan 05, 2022 at 17:40

Wednesday, Jan 05, 2022 at 17:40

How do you get on when operating in extreme COLD ambient temps, where the 'lower' tank of the radiator could be below the normal freezing point of water, but does not freeze due to the use of modern coolants. This condition will also see the transmission operating temp to be very low firstly due to the oil to water heat transfer in the radiator, and also the cooling that is naturally occurring between the air flow and the transmission sump and housing.

Yes I am old enough, and been involved with the Automotive trade long enough, to have experienced this once common occurrence prior to the modern coolants being readily available and at a price that could be afforded by the majority of vehicle owners. It was not uncommon in those days to add a substantial quantity of Metho to the cooling system in an attempt to stop the radiator lower tank from freezing, Add too much and you lowered the boiling point too far and again had overheating, but due to the lack of water.

This issue was common in all of the cooler, or higher, areas of the Eastern States from Toowoomba to the Victorian high country.

As I stated earlier, the fitment to EITHER line WILL remove heat load from the entire system.

Fitment to the cool (return) line will result in the oil temp being lowered to below radiator cool tank temp, this will also result in the oil coming FROM the transmission being cooler by approx equivalent amount, with the overall end result being the removal of some heat load from the radiator, therefore from the entire system.

Fitment to the hot line will reduce the oil temp into the radiator, and if the engine coolant is under duress then the oil will be reheated as it goes through the heat exchanger, the overall end result can be fairly similar as far as the overall cooling system is concerned, but with higher transmission temps.

AS far as your Corolla is concerned is it the transmission temp , or the engine temp, that is the governing factor?

FollowupID: 917862

Follow Up By: RMD - Wednesday, Jan 05, 2022 at 18:31

Wednesday, Jan 05, 2022 at 18:31
It is very hard to create a system to cater for both extremes. I like not taxing an already hard working engine cooling system. In cold times the cooler can be covered and then everything is effectively OE. Many autos now bypass the cooler to warm the trans and only after a set temp does normal cooling flows happen. Most times in OZ it is hot though, and towing certainly creates engine and auto heat at greater levels.
FollowupID: 917864

Follow Up By: Frank P (NSW) - Wednesday, Jan 05, 2022 at 21:35

Wednesday, Jan 05, 2022 at 21:35
Don't most aftermarket trans coolers bypass the loop in the radiator and substitute it with an air to oil cooler? Thus no trans heat going to the engine cooling circuit ever.

You just have to make sure you get a large enough cooler to do the job in hot weather. In slow going you may need to supplement it with a fan.

I had issues with my 2014 BT50 with its Ford 6R80 transmission. Loaded and towing my 2500kg hybrid its ATF temp would climb to alarming levels in the hills. I put an air to oil cooler in it, bypassing the engine coolant circuit. This fixed the uphill issue.

Perversely, then it would also overheat the ATF with extended engine braking coming down hill. It went into limp mode twice while coming down Billy Goats in the VHC (very long and steep and without the van - that would have been suicidal). Low range first and second for engine braking, consequently no airflow from road speed, ATF temps over 135. Presumably with the vehicle driving the engine the TC didn't lock (by design) and therefore generated a lot of heat.

I put the situation down to no load on the engine, therefore cool engine. Slow road speed so almost no airflow combined with the thermo clutch on the engine fan not pulling much air due to the cool engine. I added a high capacity thermo-controlled fan to the cooler and problem fixed.

Since I that mod I've never had an issue either with engine temp or ATF temp.

Lifetime Member
My Profile  My Blog  My Position  Send Message

FollowupID: 917868

Follow Up By: RMD - Wednesday, Jan 05, 2022 at 22:49

Wednesday, Jan 05, 2022 at 22:49
That is interesting to read. If you still had the OE rad cooler in circuit as well, the flow would have been cooled by the radiator on the downhill stuff. The downhill certainly churns the fluid through the TC vanes and generates heat as any speed difference of revs means work done on the fluid.
FollowupID: 917870

Reply By: qldcamper - Wednesday, Jan 05, 2022 at 15:02

Wednesday, Jan 05, 2022 at 15:02
Consider a tranny filter inline also if your tranny only has a screen internally like most others these days.
Suspended particals is the second biggest killer of tranny fluid.
I use a Cooper WTF 1 in line with my cooler and change it out every second service at 20 000 km.
AnswerID: 639008

Reply By: JayTAS - Wednesday, Jan 05, 2022 at 15:47

Wednesday, Jan 05, 2022 at 15:47
Hi all,

Thanks for the information. Upon looking at the radiator there seems to already be an auto transmission cooler fitted?

AnswerID: 639009

Follow Up By: RMD - Wednesday, Jan 05, 2022 at 16:15

Wednesday, Jan 05, 2022 at 16:15
If you follow the pipe and plumbing from that cooler, you may find it runs to the AIRconditioning system. We cannot see how long that is, but if quite long it is likely to be the aircon condenser.
Not having a Mitsubishi in front of me!
If you have aircon in the vehicle, which is normal these days and there is only the radiator AND that finned unit, it has to be aircon related. If not, how does the aircon condense the compressed gas , ie, cool it to liquid to enable cabin cooling? Three heat exchangers if rad, aircon and auto cooler are present.
FollowupID: 917861

Reply By: JayTAS - Wednesday, Jan 05, 2022 at 17:52

Wednesday, Jan 05, 2022 at 17:52
Here is another photo of where it connects near the bottom on the motor.

AnswerID: 639011

Follow Up By: RMD - Wednesday, Jan 05, 2022 at 18:13

Wednesday, Jan 05, 2022 at 18:13
Yes, you are correct, it certainly looks like an auto cooler given hose clamps and banjo fittings. You have a cooler so no need to add more. Enjoy!
FollowupID: 917863

Follow Up By: Athol W1 - Friday, Jan 07, 2022 at 09:39

Friday, Jan 07, 2022 at 09:39

I agree with RMD in so far as what you have shown certainly appears to be an oil to air cooler of original manufacturer fitment, however I would still be fitting an additional cooler if there is any doubt, or hint of high transmission temps being attained.

Some time back I had a Toyota LC200 and I was advised by the local Toyota dealer to fit an additional cooler, even though these vehicles are fitted with 2 coolers (oil to water and oil to air), even with the 3 coolers in the system some of the highest transmission temps occurred when towing my 3 tonne van and going DOWNHILL on some stretches of the New England Highway that occurred very soon after a long uphill run. Engine temp dropped so the efficiency of the oil to water cooler increased, however the additional heat being generated within the torque convertor exceeded the heat that was being removed via the oil to water system.

Vehicle manufacturers will only fit what is required to ensure the vehicle will pass out of the warranty period with NORMAL (what ever that means) use. They will leave out a bolt if they think they can get away with it just to save a few cents per vehicle. I have seen them leave out 2 thrust washers in an auto transmission to save a few cents, they miscalculated on that one as the life of those transmissions was just 10,000 miles when the warranty was 12,000 miles (yes just a few years back)

FollowupID: 917884

Follow Up By: RMD - Friday, Jan 07, 2022 at 14:20

Friday, Jan 07, 2022 at 14:20
I pretty well agree with Athol in that an additional cooler may be required for the BAD times.
It seems, I don't know for sure, but appears the auto ONLY has that cooler and none in the radiator cool side/end. Only by checking the pipes from auto to cooler and where they go before being returned to the auto, will you know if it is in fact the sole cooler provided by Mitsubishi, or it has a radiator heat exchanger too. If it is the only cooler, it should have a thermo controlled fan assist especially for the fluid cooler. You may have to, AT LEAST provide a switchable fan to get rid of heat when conditions dictate high temps will be happening if sole cooler and no fan. Any additional cooler or OE cooler will still allow high temps in adverse conditions with no airspeed through them. It is the towing mass which creates the additional heat stresses which must be controlled.
Only other way, at times, is to travel in low gear at higher engine revs and hope the lesser imposed load and fast engine or electric fan speeds and fluid circulation can control any temp rise. Most people don't want to run slow as a management strategy though!
FollowupID: 917888

Sponsored Links