FSD/PMD "Points to Ponder" How hot does it get

[ak diesel driver]

from everything I've read/ experienced it's not so much about keeping it cool as minimizing the thermal shock or expansion and contraction cycles. I had one fail only in subzero weather, when it warmed up it was fine

 

[Burning oil]

New 6.5 owner here. Just traded a 92 Cherokee Limited (plus $2400 cash) for a very nice, original 95 Suburban LT. I have an idea I wanted to propose here and see what all the experts thought of it.

I have a peltier cooler from one of those little 12v beverage chillers laying around in my shed. It has a fan on the warm side, and what I'm thinking of doing is taking off the cool side heatsink and sandwiching the peltier element between the aluminum plate side of the PMD and the fan-cooled hot side heat sink. Then I could remote mount the resulting PMD/cooler "package" in the cab connected to a switched 12v source.

With the peltier cooler and fan it wouldn't need air circulation from the AC system - it will make ts own cooling. No need to weatherproof the PMD. Seems simple and reliable enough.

Any thoughts?

from everything I've read/ experienced it's not so much about keeping it cool as minimizing the thermal shock or expansion and contraction cycles. I had one fail only in subzero weather, when it warmed up it was fine

x2 Thats pretty much it.

We did some testing with Peltier type heat sinks and found them unnecessary. Its just alittle more complicated to with having to run wires...
You can use the heat sink without powering it up though. It should'int hurt anything to power it up, just not necessary.

 

[Turbine Doc]

There are multiple fail modes heat direct component damage is but one of them, also thermal cyclic fail, electrical current issues from poor gnds, and crappy individual components, many years ago at old site I did a survey fail location vs time installed #1 fail location was on IP, #2 was under hood, best survival rating was out of engine bay, as always in any data set there are the "odd man out" fails or survivals that are exceptions .

 

[CheaperJeeper]

Cool (pun intended )

I think I'll simplify and leave the peltier element out of it altogther. I like the idea of putting it in the cab where it is in a relatively climate-contolled environment and will stay nice and dry. However I want to make sure it gets enough air flow, so I think I'll go ahead with using the heatsink AND fan to ensure some steady air circulation.

 

[Will L.]

I like the idea of putting it in the cab where it is in a relatively climate-contolled environment and will stay nice and dry. However I want to make sure it gets enough air flow, so I think I'll go ahead with using the heatsink AND fan to ensure some steady air circulation.

It's been tried by a few here, myself included. There is a reason everyone keeps saying inside the front bumper...

 

[bison]

It's been tried by a few here, myself included. There is a reason everyone keeps saying inside the front bumper...

Not everyone,i beg to differ,...see post #70

 

[Will L.]

I'm sorry Bison, you are right. I should have said most. No offense intended:sad6:

Most people found the best location was on the bumper. In the desert testing fleets we tried a couple under hood spots and in the cab in a few spots. Our best results were on bumper but different climates give different results.

 

[CheaperJeeper]

It's been tried by a few here, myself included. There is a reason everyone keeps saying inside the front bumper...

Yeah, and having read this whole thread in one sitting I concluded that reason is air flow. That's why I plan on using a heatsink with a fan - to give it that constant airlow.

Earlier posts also indicate that minimizing the range of the temperature cycling is almost as beneficial as keeping it cool. There's no question that inside of the cab is a much more temperature controlled environment than behind the bumper.

The other issue is the one of weatherproofing. Water promotes corrosion - another significant cause behind one of the primary failure modes. This may not be a big concern in the deserrt, but it is definitely a significant concern here in the great north WET. It seems to me that locating it behind the bumper would not only expose it to more water induced corrosion, but would also put it at risk for a BIG thermal shock - if a hot PMD got hit with a big splash if cold rain.

 

[ak diesel driver]

Mines in the engine bay right next to the drivers side batt.

 

[bison]

Yeah, and having read this whole thread in one sitting I concluded that reason is air flow. That's why I plan on using a heatsink with a fan - to give it that constant airlow.Earlier posts also indicate that minimizing the range of the temperature cycling is almost as beneficial as keeping it cool. There's no question that inside of the cab is a much more temperature controlled environment than behind the bumper.

The other issue is the one of weatherproofing. Water promotes corrosion - another significant cause behind one of the primary failure modes. This may not be a big concern in the deserrt, but it is definitely a significant concern here in the great north WET. It seems to me that locating it behind the bumper would not only expose it to more water induced corrosion, but would also put it at risk for a BIG thermal shock - if a hot PMD got hit with a big splash if cold rain.

That is the reason i mounted mine in the engine air intake flow path in the pass side fender,..The FSD is allways dry and easy to change out if need be.

 

[ak diesel driver]

one of the reasons I kept mine in the engine bay was the extra cold temps we see here. In the engine bay it will cool off a lot more gradually when it's -40 and I turn the engine off.

 

[Burning oil]

Yeah, and having read this whole thread in one sitting I concluded that reason is air flow. That's why I plan on using a heatsink with a fan - to give it that constant airlow.

Earlier posts also indicate that minimizing the range of the temperature cycling is almost as beneficial as keeping it cool. There's no question that inside of the cab is a much more temperature controlled environment than behind the bumper.

The other issue is the one of weatherproofing. Water promotes corrosion - another significant cause behind one of the primary failure modes. This may not be a big concern in the deserrt, but it is definitely a significant concern here in the great north WET. It seems to me that locating it behind the bumper would not only expose it to more water induced corrosion, but would also put it at risk for a BIG thermal shock - if a hot PMD got hit with a big splash if cold rain.

Actualy it stays a more consistant ambeint (sp?) temp behind the bumper. Inside the cab can reach 140 + degrees on summer days then drop to 40-80 degrees with a/c on while the same truck with a bumper mount is only "room temp". There may be exceptions like living where its -40 like Les & Bison, but for most app's bumper mount works great and no need to run a fan.
As far as weather/water go's the PMDs are waterproof the one exception being the pins on the connector. They have a nice seal, but its recomended to squeeze a blob of dielectric greese in there to waterproof them. Also always point the female connector body of the PMD down so water cannot stay in there.
I've sold a couple thousand PMDs and its a very rare problem (cant think of any) that will have corroded pins.
To be clear Im not arguing with you just stating my observations on the many units I've sold.

 

[CheaperJeeper]

Actualy it stays a more consistant ambeint (sp?) temp behind the bumper. Inside the cab can reach 140 + degrees on summer days then drop to 40-80 degrees with a/c on while the same truck with a bumper mount is only "room temp". There may be exceptions like living where its -40 like Les & Bison, but for most app's bumper mount works great and no need to run a fan.
As far as weather/water go's the PMDs are waterproof the one exception being the pins on the connector. They have a nice seal, but its recomended to squeeze a blob of dielectric greese in there to waterproof them. Also always point the female connector body of the PMD down so water cannot stay in there.
I've sold a couple thousand PMDs and its a very rare problem (cant think of any) that will have corroded pins.
To be clear Im not arguing with you just stating my observations on the many units I've sold.

Good points - I can see the temp swing you're talking about in a lot of places - in hot climates when you have a working AC system and use it. None of those conditions apply in my case

I was of the impression that the aluminum back plate of the PMD doesn't come sealed to the plastic body of the unit. Did I get some bad info somewhere?

You guys have about sold me on the bumper mount - but that's what I'm here for - advice from those with more experience with the quirks of this particular engine/vehicle combination...

 

[Burning oil]

I was of the impression that the aluminum back plate of the PMD doesn't come sealed to the plastic body of the unit. Did I get some bad info somewhere?

The componeints inside are potted in a epoxy type compound to waterproof them. The transistors are exposed though, I recomend after mounting to heat sink to run a bead of Goop sealant around the base to seal PMD to the heat sink.

 

[CheaperJeeper]

The componeints inside are potted in a epoxy type compound to waterproof them. The transistors are exposed though, I recomend after mounting to heat sink to run a bead of Goop sealant around the base to seal PMD to the heat sink.

That's the waterproofing I was talking about. I hate the idea of gluing it to the heatsink and the possibility of it not being water-tight...

 

[Burning oil]

Why do you hate the idea of sealing it? These trucks need alot of little tricks. If you bring the cable into the cab where are you going to pass though the firewall without making a huge hole?