M1089A1 Trans Cooler Question

[h1x2]

Newly acquired truck. Haven’t driven it much and haven’t gotten a chance to tackle the manual yet.

Drove it today for about 30 minutes then the trans temp light came on. Neither cooling fan was on and no power at the connector. Trans and cooler were hot. Shut the truck down. Turned the ignition on and both fans turn on. If I start it, they shut off.

I’m not very familiar with these trucks so I wanted to put this out on the forum before I start diagnosing it.

Also, the fan cut off switch will shut these off if activated when the ignition is on.

Are the fans supposed to turn on when the ignition switch is turned on?

 

[Third From Texas]

Newly acquired truck. Haven’t driven it much and haven’t gotten a chance to tackle the manual yet.

Drove it today for about 30 minutes then the trans temp light came on. Neither cooling fan was on and no power at the connector. Trans and cooler were hot. Shut the truck down. Turned the ignition on and both fans turn on. If I start it, they shut off.

I’m not very familiar with these trucks so I wanted to put this out on the forum before I start diagnosing it.

Also, the fan cut off switch will shut these off if activated when the ignition is on.

Are the fans supposed to turn on when the ignition switch is turned on?

The M1089 is beyoind my scope (only had the four wheel variants myself).

Wild guess, but could it be a failed temp sensor?

Ie: the engine fan will come on at start up but then shut down until the 200 degree mark where the sensor turns it back on

Perhaps the trans cooler works in a similar fashion but is not kicking in?

I imagine you could certainly bypass such an issue with a manual override and keep the trans-cooler fans on full time via the ignition or accessory switch...

 

[coachgeo]

M1089 fan works like any other FMTV when it comes to what turns them on and off. Not sure if they system is duplicated for a rear fan as it is for engine fan or if the one air solenoid activates both.... but conceptually..... once you understand one of them you should understand both.... granted I am assuming there is a fan on the cooling system behind the cab and that system is for the trans. For all I know that is different and is for the hydraulic oil cooling.


so with that in mind.... search in this forum for "(anyFMTV) A1 fan " or xxxxxA1 fan hot?? or something similar*
examples:
M1089A1 fan
M1078A1 fan
M1088A1 fan

*even leaving out the A1 part is liable to get you info. that you can infer with

 

[h1x2]

Thanks for the replies.
Found out the aux fan comes on with the engine fan which didn’t work well because my engine temp was fine when my trans was running hot.

Planning on adding a temp switch to the trans line somewhere and having the trans fans turn on independently, and with the engine fan. Also going to add a trans temp gauge and light indicating when the aux fans are on.

We’ll see how that goes. Spent quite a bit on this truck, was hoping it was going to be reliable.

 

[Ronmar]

The 1089 has a liquid heat exchanger/cooler down between radiator and oil pan like any other LMTV, so you shouldn’t be overheating just the trans if you are not working it hard enough to need an aux cooler.

If I recall correctly from a discussion with a gentleman who was relocating the aux cooler down between the frame rails for a habitat build, there is also some sort of thermal mixer/diverter valve in the transmission fluid lines. If that has an issue, it might not be sending the hot fluid to the liquid cooler to cool it, or to push the engine coolant temp over the threshold to activate the fans.

As you discovered the aux cooler fans are controlled by the engine fan thermal control. On the A0 it’s a 205F normally closed thermal switch in the upper radiator pipe, but in the A1/A1R the engine ECU controls the fan…

The fan controls are reverse logic. Power is applied to keep the fans off, and removed to engage the fans. Power to keep the fans off is either applied from the ECU/thermal sw, or via the fording switch from CB22. You can force the fans on/manually control them by removing CB22 and then selecting the fording/fan off position on the fan control switch. Without CB22 providing the fording switch power, this will remove power from the engine fan solenoid and the aux fan relay(K15), turning both fan groups on. Switching it back to the fan on position will give fan control back to the ECU which if not overheated will provide the power for both solenoid and aux fan relay, turning both the fans off… This will allow you some manual control until you can figure out why the liquid cooler isn’t delivering the transmission heat into the engine coolant like it is supposed to…

CB22 also powers the intake grid heater control, so no air heat for clod starts while it is pulled.

Good Luck.

 

[h1x2]

The 1089 has a liquid heat exchanger/cooler down between radiator and oil pan like any other LMTV, so you shouldn’t be overheating just the trans if you are not working it hard enough to need an aux cooler.

If I recall correctly from a discussion with a gentleman who was relocating the aux cooler down between the frame rails for a habitat build, there is also some sort of thermal mixer/diverter valve in the transmission fluid lines. If that has an issue, it might not be sending the hot fluid to the liquid cooler to cool it, or to push the engine coolant temp over the threshold to activate the fans.

As you discovered the aux cooler fans are controlled by the engine fan thermal control. On the A0 it’s a 205F normally closed thermal switch in the upper radiator pipe, but in the A1/A1R the engine ECU controls the fan…

The fan controls are reverse logic. Power is applied to keep the fans off, and removed to engage the fans. Power to keep the fans off is either applied from the ECU/thermal sw, or via the fording switch from CB22. You can force the fans on/manually control them by removing CB22 and then selecting the fording/fan off position on the fan control switch. Without CB22 providing the fording switch power, this will remove power from the engine fan solenoid and the aux fan relay(K15), turning both fan groups on. Switching it back to the fan on position will give fan control back to the ECU which if not overheated will provide the power for both solenoid and aux fan relay, turning both the fans off… This will allow you some manual control until you can figure out why the liquid cooler isn’t delivering the transmission heat into the engine coolant like it is supposed to…

CB22 also powers the intake grid heater control, so no air heat for clod starts while it is pulled.

Good Luck.

Thanks for the response. That gives me some clarity before I get this pulled in the shop.

So you’re saying the trans fluid and coolant go to some type of mixer to equalize temp? That would make sense to me now that the trans fans are controlled by the engine fan.

 

[Ronmar]

On the 4 wheelers, the trans fluid flows forward thru a heat exchanger on the lower radiator pipe, dumping its heat into the coolant that is headed back towards the engine. The cooled trans fluid then flows back to the trans. Basically the same as any automatic trans pickup…

On the units with the aux cooler, I think it is a thermal mixing valve in the trans fluid plumbing. I suspect it is supposed to keep the fluid flowing towards the liquid cooler until it gets really warm, to keep from sending cooler fluid toward the aux cooler when it’s really cold out/lightly loaded and over-cooling the oil.

I have only seen pics of one, and havn’t looked at that plumbing circuit…

An IR thermometer on some of the fittings should be able to tell you where the hot fluid is going…

 

[h1x2]

On the 4 wheelers, the trans fluid flows forward thru a heat exchanger on the lower radiator pipe, dumping its heat into the coolant that is headed back towards the engine. The cooled trans fluid then flows back to the trans. Basically the same as any automatic trans pickup…

On the units with the aux cooler, I think it is a thermal mixing valve in the trans fluid plumbing. I suspect it is supposed to keep the fluid flowing towards the liquid cooler until it gets really warm, to keep from sending cooler fluid toward the aux cooler when it’s really cold out/lightly loaded and over-cooling the oil.

I have only seen pics of one, and havn’t looked at that plumbing circuit…

An IR thermometer on some of the fittings should be able to tell you where the hot fluid is going…

Ran it hard today to do some diagnostics and testing. Went over the whole thing with a thermal imager. Showing equal temps at the heat exchanger under the radiator. I almost feel like this is to get the trans up to temps in the cold.

With the engine running at 180-190 degrees, trans cooler temp was 225degrees. Decided to add a temp switch to the trans and turn the fans on independent of the engine. Hopefully this resolves some issues. Going to do filters on the trans at the same time because I don’t know when they were done last.

 

[B-Dog]

On the 4 wheelers, the trans fluid flows forward thru a heat exchanger on the lower radiator pipe, dumping its heat into the coolant that is headed back towards the engine. The cooled trans fluid then flows back to the trans. Basically the same as any automatic trans pickup…

On the units with the aux cooler, I think it is a thermal mixing valve in the trans fluid plumbing. I suspect it is supposed to keep the fluid flowing towards the liquid cooler until it gets really warm, to keep from sending cooler fluid toward the aux cooler when it’s really cold out/lightly loaded and over-cooling the oil.

I have only seen pics of one, and havn’t looked at that plumbing circuit…

An IR thermometer on some of the fittings should be able to tell you where the hot fluid is going…

Unless the mixing valve is integrated into the aux cooler, I'm almost certain the coolers are simply in series. My only hesitation is suggesting Ronmar is mistaken

But, it would be better to bypass the aux cooler unless it was needed so I could be wrong.

 

[Ronmar]

Unless the mixing valve is integrated into the aux cooler, I'm almost certain the coolers are simply in series. My only hesitation is suggesting Ronmar is mistaken

But, it would be better to bypass the aux cooler unless it was needed so I could be wrong.

I found it with a search, It was Ramdough and we were discussing new hose lengths for his cooler relocation back by the axles. Here is a pic of the unit in question Located right behind the transmission.

https://www.steelsoldiers.com/attachments/6d29f4ff-8169-4e7d-b267-a24f04f09a24-jpeg.838106/

A thermal bypass/regulator was the only purpose that seemed to make sense in the system. It would make more sense to me for the aux cooler to simply be inline after the liquid cooler, but his had this valve block…

Here is a link to that discussion...

Moving my Transmission cooler

So, I need to relocate my transmission cooler. I am looking at putting it right behind my rear axle (where my frame has been extended). This will mean longer hoses. I have a few questions: Once I disconnect the line, I assume a bunch of oil will drain out. I can put a bucket to catch the oil...

www.steelsoldiers.com

 

[Ronmar]

Ran it hard today to do some diagnostics and testing. Went over the whole thing with a thermal imager. Showing equal temps at the heat exchanger under the radiator. I almost feel like this is to get the trans up to temps in the cold.

With the engine running at 180-190 degrees, trans cooler temp was 225degrees. Decided to add a temp switch to the trans and turn the fans on independent of the engine. Hopefully this resolves some issues. Going to do filters on the trans at the same time because I don’t know when they were done last.

On the A0, they ran the bypass coolant from the thermostat housing down to a port on the left of the trans heat exchanger, and that is exactly what it does, it dumps all the engine heat into the transmission until it warms up(horrible way to run a diesel). They did away with this “feature” on the A1/A1R As the EFI engines run better with a consistent engine temp, As does any diesel

That heat exchanger and the radiator provides the ONLY cooling on the 2.5-5 ton LMTVs. It should be providing ALL your cooling unless you are pulling a trailer…

 

[B-Dog]

I found it with a search, It was Ramdough and we were discussing new hose lengths for his cooler relocation back by the axles. Here is a pic of the unit in question Located right behind the transmission.

https://www.steelsoldiers.com/attachments/6d29f4ff-8169-4e7d-b267-a24f04f09a24-jpeg.838106/

A thermal bypass/regulator was the only purpose that seemed to make sense in the system. It would make more sense to me for the aux cooler to simply be inline after the liquid cooler, but his had this valve block…

Here is a link to that discussion...

Moving my Transmission cooler

So, I need to relocate my transmission cooler. I am looking at putting it right behind my rear axle (where my frame has been extended). This will mean longer hoses. I have a few questions: Once I disconnect the line, I assume a bunch of oil will drain out. I can put a bucket to catch the oil...

www.steelsoldiers.com

I do vaguely remember that picture. My M1083 A0 certainly did not have that.