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Discussion Starter #1
Moved PMD to the left side fender, install computor fan, heatsink and temperature thermostat to come on 90 degees and off at 80 degrees system working ok. Going to do more testing on longer milage runs.
Parts use, computor powersupply fan and computor heatsink and temperature thermostat from Lowes mastor flow model pt6 60 to 120 degrees use in attic fans. Install units in medal electric box. Very easy to install. All computor parts came out junk computors. cost $18 Going to at a later time install temp gauge to see what temp PMD true temp is running.
 

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Cool let us know how it works.
 

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Now all you need is some cool air to blow over it. Underhood temps tend to get quite high. Blowing hot air over the unit may heat the PMD if thats possible.
 

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Yes, I'm afraid there is no way to make a good under hood cooler.

When it shuts off the heat will go up to well over the safe temp for the module, and the change in temperature from hot to cold is damaging.

Just weatherproof it put it behind the bumper and it stays cool.
 

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Just curious, what exactly are the "safe temps" for these things? I agree that heat soak is an issue when mounted under hood as I have a temp gauge mounted to my PMD that is mounted on the firewall. Minimized that with a fan mounted above it that has a high cfm rating and a mechanical timer for after shut-down. I did get carried away a bit and ducted outside air to flow over the heat sink as long as the truck is in motion. It may not be the most ideal location or set-up but with the limited harness I had it was the best I could do, for now. Been in place for over 3 years and still working, knock on wood.:rolleyes:

Also, DieselPro brings up a valid point as the PMD will definitely get hotter with fan on while driving as it is just pulling hot under hood air over the heat sink. Get some fresh outside air moving over it some way. If and when you put a temp a gauge on it you'll see they get plenty hot in a big hurry and need all the help they can get to keep cool. That's why most recommend to mount outside for best chance to keep temps down.
 

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Most silicon transistors will begin to degrade above 175F and fail above 300F.

The unit construction is also a factor. The coupling of the transistors with the circuit is believed to fail due to repeated large temperature fluctuation cycles.


In the case of the one under my hood it was too hot to touch at times. Not sure how hot that was. Many people have good luck with them. I think it depends on the individual unit and the conditions under your hood.


Also with my recent experience I would say that the high temperatures do cause a change in the performance of the unit which when coupled with an inferior optical sensor in the IP that's on it's way out will cause the problems we see sometimes.
 

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Thanks David. When first mounted with just heat sink it was almost too hot to touch, which I guess is a good thing as heat sink was doing its job. With set-up I now have heat sink is cool and PMD is just barely warm. During summer driving conditions (90F+) I would see a spike of about 140 while sitting and then once moving again it would settle down in the 115 to 120 range. Yesterday temps were in the 40's and PMD climbed to a high of around 99 and then dropped down to the high 70's while moving.

Do you think that this kind of temperature fluctuation will be detrimental or are they within the parameters of normal operation? BTW, have not re-tightened anything since install.
 

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Discussion Starter #8
Tried mounted pmd under bumper, had problems with mosture on leads and on pmd. I run in water sometimes up to the bumber and highter.
I thank I will try running outside air duct up to fan like to cool pmd down
to lower temp as i can.
 

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Yea, if the temperature is comparable to outside temps I'm not sure what you could do to make it any better.


When mine was extremely hot I think it was the engine heat that was heating it up and not the FSD. Mainly because with it away from the engine heat it does not get hot at all.

Also, trying it on the engine with the FSD not in use it still got hot.
 

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You have worked so hard to build up the FSD cooler, why not try to put it inside the passenger? Probably on the firewall behind/under the dash? There is no water there, hopefully. Just a thought.
 

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I have my pmd mounted under the steering colum in the cab on a cooler. The pmd wil get to almost 130 degrees with the heater on. I've been thinking of moving it to under the front bumper, but am worried about moisture. But so far so good.:cool:
 
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