...unless you have spares!

Yesterday, I was cleaning/protecting all the connectors under the hood of the '86 that I could reach, when I decided that it would be a good idea to put new heat transfer paste under the ignition amps.

Bad idea. The old paste had turned into a glue which was stronger than the glue which holds the amps together! Both of them separated, and the little wires to the hybrid chip pulled out.

On a good note, I wanted to replace them eventually anyway, and my LAPS (Halsey Import), ordered for Monday (from WorldPAC), german made Hüco's, for only $32 each.

Ignition switch unit - 928 602 706 01 - Bosch 0 227 100 124
Also used on later 944, 924S, Carrera2/4.

 

Dayum. Never heard of that before. I've renewed the heat sink paste on a number of 87+ and never had anything close to that problem.

Maybe a good idea to renew the paste before it's 20 years old?

 

.... sometimes it's even a better idea to leave things alone until they break without assistance ... that's what keeps a spare as a spare ...

 

Hey guys, tell us more about this heat transfer paste! I've never heard of it before. We're talking about those finned boxes just next to the hood latch, right? This paste is supposed to help dissipate heat faster, is that correct?

 

Yes, quite common. It helps tranfer heat from the board/chip/enclosure to another mounted surface. Almost all main processors in computers will have thermally conductive paste between the chip and the aluminum heat sinks.

 

thanks, JP.

 

From Big Dave's book of auto repair:

If it's not broken - fix it until it is!

 

The ignition stages are on the front right of the car - looking at the engine bay from the front. They're under a 2"x6" plastic cover in front of the light bar. The black box with the heat dissipation fins is for the electric fans IIRC.

 

Silicone grease should never harden, so maybe it was replaced once before with some kind of glue?

 

I don't know if the heat sink paste Porsche used at the factory was silicone-based or not. But, whatever they used is as hard as glass after 10+ years. I've renewed the paste on at least 6 928s and in all cases it was hard. The 'new' stuff invented to allow a <1" square IC to dissipate 200w without self-immolation is a lot better than what they had lying around in 1986. Maybe it will still be tacky in 2012 when I renew the paste on my fleet again.

According to what I found when looking into it several years ago, the apparent most common failure mode for the ignition stages is heat.

 

White thermal slicone paste and silicone dielectic grease have been used for along time to help ignition modules transfer the heat they create. The paste tends to harden after a long time.

 

If someone who has one of these apart would care to experiment, it would be good to find out what it takes to loosen that paste. WD-40, PB Blaster, Kroil, etc? Maybe there's something that won't harm paint or plastic but will loosen those suckers right up.

 

S.A.V.E is another one

 

Big recall on Fords for failure of the ignition module on the distributor. It had the white heat paste, but, alas, it was still too hot and the units often failed. Aftermarket has remount kits which move the unit to a cooler spot. The grease Ford used stayed quite soft - I've removed many and they aren't too stuck. I can't believe our units get that hot based on where they are. Heat must be internal. On the Fords I don't know which way they expected the heat to flow - the engine had to be hotter than the chips - what were they thinking? I think ours are in a great spot (as long as water isn't an issue).

 

Ken, yes I have posted that caveat before .... sorry Dude those are expensive little suckers.