so today i finally got my PMD moved out of the engine compartment. the next step was to find a heat sink but i didnt feel like paying a ton of money for a hunk of aluminum. being the ham radio packrat that i am i never throw away anything. digging through my many boxes-o-crap i found a dead ham radio amp with a nice sized heat sink.... can you guys tell me if this heat sink is big enough?? im sure its probably better than being mounted on the ip but i want to be sure. also i mounted it right under the bumper with the fins facing down to get some air flow while driving down the road, but im not sure its a GOOD location... i wouldnt want to hit something and have it break off.

http://kc8yhk.hopto.org:8085/mike/truck/pmd1.jpg

http://kc8yhk.hopto.org:8085/mike/truck/pmd2.jpg

http://kc8yhk.hopto.org:8085/mike/truck/pmd3.jpg

http://kc8yhk.hopto.org:8085/mike/truck/pmd4.jpg

looks big enough. Heat sinks need 2 things: enough mass to take the heat away from your PMD, and enough surface area to radiate it away faster than your PMD can generate it.

The fins take care of the Surface area part fine, and the back of it LOOKS thick enough to me, but it's hard to say from the photo. The mass is important more when you're sitting still than when you're moving, with cool air running over it.

Correction: 3 things - a good thermal-transfer compound between the heat sink and the PMD is also needed.

Why not mount it facing 'up' in the bumper nostril? That will keep it outta the way.

Why not mount it facing 'up' in the bumper nostril? That will keep it outta the way.


good idea, thanks. i will try and mount it there later this week if time allows.

good idea, thanks. i will try and mount it there later this week if time allows.

Hey, I just had another look at your pictures... try and mount it so the fins are parallel with the airflow, not perpendicular like your pic shows... you'll build up a pressure wave on the first fin and the air will just go right over the others, kind of like a bug-deflector on your hood.

Won't cool worth beans that way, and will be hard to get at to clean. If it's parallel with the axis of the truck, you can just spray the bugs + mud out of it.

Get this... i sound like I know what I'm talking about. Hoo-boy.:muahaha:

Get this... i sound like I know what I'm talking about. Hoo-boy.:muahaha:
You must have stayed at a Holiday Inn last night

You must have stayed at a Holiday Inn last night
:funnypost

As an added precaution face the driver plug socket aft, the weather Pak seals are good but 70+ mph of ram effect could drive moisture into the pin socket

As an added precaution face the driver plug socket aft, the weather Pak seals are good but 70+ mph of ram effect could drive moisture into the pin socket

That is a good idea. Wouldn't have thought of that.

I have thought of putting it in the passenger side frame rail. On my drivers side, there is a power steering cooler in there so I figure air flow through them has got to be pretty good. While in the frame rail, it would be about as safe as anywhere else too.

I have them every now and again in spite of my advancing years, a cell snaps the right direction and generates what passes for a good idea

Actually, I wouldn't put it into the Passenger-side nostril unless you have done some air intake mods (like removed the airbox...) The stock airbox and snorkle drinks air from that hole, and it can't get enough as it is.

I'd put it in front of the PS cooler.

His 97 doesn't have the restrictive fender snorkle, and F upper should be free flowing non EGR non slitted one, but worth a check as some F's got the restrictive upper,

The round airbox also flow better than the square one, and running with lid off air box in summer isn't best idea

Yep, I agree. Actually, I was thinking more along the lines of an airbox replacement (like the K&N cone, or the ones Walt or John sell) ... didn't mean to hint that he should just take the durn thing off (gotta be more careful with that. I knew what I MEANT to say...). Sorry

There is a formula for determining if a heat sink will keep an electronic component cool enough. I found it on the web a few months ago when I was trying to fabricate a remote mount ( I ended up putting in a Heath versus making my own). I cannot find the formula just now. The variable I was never able to find out is how cool do we need to keep the FSD.

What type of adhesive is needed to do this mod?
and do you have to drill into heat sink to mout it?

I don't think I would just trust an adheasive. Depending on the thickness of the heat sink you might have to drill and tap.

mechanical fastener is sufficient, Heaths driver is also bonded with a epoxy (I don't know what kind) that also conducts heat transfer, flatness is also a player for good heat transfer.

What type of adhesive is needed to do this mod?
and do you have to drill into heat sink to mout it?

i drilled 4 holes then went out and bought a cheapie tap & die kit and it worked perfectly.

Good move... I would have screwed it down, too. Did you use any heat sink compound (Thermal Transfer Paste) or a silicon transfer pad between the PMD and the Heat Sink?

That's pretty important - the back of my PMD wasn't all that flat, and a lot of heat would build there around the transistors without having a good mass to drain it off... air is a lousy heat conductor. I've seen p3 and p4 chips fried because the heat sink in a PC wasn't properly conducting from the chip.

If it were me, I'd goop it up pretty good.

there was a silicon pad there already so i re-used it when i installed the pmd on the heat sink. i wanted to get some paste but couldnt find any on a sunday night... so maybe this weekend i will get to it. its ok for now though because my truck is parked at the yard at work and my 18 wheeler ( a real diesel haha) is my ride for the rest of the week.

so where can I get that paste and what is it called?

you can get some from radioshack http://www.radioshack.com/product/index.jsp?productId=2216879&cp=&origkw=thermal&kw=thermal&parentPage=search

its called thermal gel or thermal compound

I second jifaire's #3 comment - you also need a good heat transfer compound between the heater and the fins. You can get some at a computer geek store.
But tell me - a PMD doesn't generate its own heat does it? It just absorbs heat from the engine were it is normally located? If so, a heat sink is probably not necessary once it has been moved away from the heat source.

Unfortunately, no. If you hang one on a harness without a heat sink and start the truck, you can have it smokin in about 5 minutes. A heat sink is a definite necessity - that's why GM mounted it on the pump in the first place... they figured the circulatig Diesel fuel would absorb and take away the heat, which it mostly does. What they forgot about was what happens after you shut the truck off... the heat in under the manifold just keeps going up and it 'soaks' into things because there's no airflow, coolant flow, or fuel flow to take it away.

Therefore the term 'heatsoak' which gets applied to these little buggers.

You can boil water on a PentiumIII chip without a heatsink/fan on it... these things have 2x500w transistors on the back, and can get hotter than that.

All that being said, though, if the silicon pad hasn't lost it's pliability, it will likely do the job.

you can get some from radioshack http://www.radioshack.com/product/index.jsp?productId=2216879&cp=&origkw=thermal&kw=thermal&parentPage=search

its called thermal gel or thermal compound

Thanks for all that good information.:beerchug:

As an added precaution face the driver plug socket aft, the weather Pak seals are good but 70+ mph of ram effect could drive moisture into the pin socket

Gee, the man's thinking. Some more thoughts (after hundreds of cables and coolers...)

That small green seal on the back of the connector that the wires push through. It can be removed (carefully) and you can pack more silicone dielectric grease in there (the seal is coated from teh factory, but could use more). Also well coat the other (blue) seal with dielectric grease too. That seal will also slide off if you want to remove and clean it.

Mount with the fins aligned with the air flow (as mentioned in another reply), or with the fins facing the air flow (so the pmd is to the rear) behind the grill (but not blocking the radiator too much if possible.)

As to the OPs original question, I'd say his cooler is sufficient. It could have a few more fins or be a bit larger, but as long as it gets a good flow of cooling air it shoudl work OK. The heat buildup is directly proportional to engine seed (and therefore vehicle speed) so forced air cooling is really a good thing.

:grd:

thanks for all the input guys, i moved the PMD/Heat sink to the hole in the bumper on the left side of the license plate (passenger side). using some scrap steel i made a simple bracket so the fins face outward. then i went to radio shack and bought some thermal compound and gooped up the back of the PMD really really good... used too much really.

then i took a 40 mile round trip at mostly 65 MPH and the pmd and heat sink were totaly cool to the touch!

its kind of hard to see in this pic but it gives you an idea.
http://kc8yhk.hopto.org:8085/mike/truck/pmd5.jpg

thanks again for the advice,
Mike

Now that looks near perfect. But i still aint moving mine from where it is, lol