Thermal paste??

[Ian Fife]

I read a post on the USA Volvo forum about renewing the thermal paste under the ignition power module. The recommendation was to renew the thermal paste every 2-3 years.
This is the first I've ever heard of thermal paste, let alone the need for regular renewal.
My 1991 945 has never had any attention in this area, and has never given any trouble.
Any thoughts anyone?

Ian F

[bob12]

In 32 years with the 745 I have used thermal paste only twice.

Once when I had to take the ign amp off the inner wing and the other when I had the audio amp to pieces.

I have not heard of it being necessary to replace every few years! All it's there for is to assist with the dissapation of heat from the amp more readily. When you take the ign amp off the inner winng the paste looks pretty sound.

Bob

[Ian Fife]

Thanks Bob, I will hold off buying any for the time being!

Ian F

[Laird Scooby]

If it's never been done, buy some heat sink compound, remove the ignition amp and clean the back of it and the heatsink with a solvent cleaner and polish both to as near mirror finish as you can get with minimum effort. DO NOT use anything abrasive!

Once clean, degrease the surfaces with meths, carb or brake cleaner, petrol or similar and once dry, apply a smear of heatsink compound (aka thermal paste) onto the mating face of the ignition amp heatsink. Apply the amp to the main heatsink and move it around to spread the compound around then refit the screws, plug etc and test.

While you're working in that area, follow the wiring harness back until you find the earth cable for the ignition amp near the suspension turret base, undo the screw/bolt and clean the crimp terminal with a wire brush, emery paper or similar and likewise clean where it attaches to the body and also the bolt/screw.
Smear some silicone grease on the threads and the terminal and refit, spreading the squeezed out grease over the screw head, terminal etc to cover it making it waterproof again.

[Forrest]

The Americans seem to advocate a lot of potentially unnecessary or overly-frequent maintenance tasks.

My view is that the thermal compound only needs replacing if you have to remove the component from the heat sink for any reason. In those circumstances it is essential to clean everything up thoroughly and refit with new paste as described above.

The compound is grease in a confined space. It's not going to deteriorate that rapidly unless the heat sink is badly fitted in the first place.

Similar thermal compound is used in computers and amplifiers. I've got amplifiers over 50 years old that have never required such maintenance.

[Laird Scooby]

Originally Posted by Forrest

The Americans seem to advocate a lot of potentially unnecessary or overly-frequent maintenance tasks.

My view is that the thermal compound only needs replacing if you have to remove the component from the heat sink for any reason. In those circumstances it is essential to clean everything up thoroughly and refit with new paste as described above.

The compound is grease in a confined space. It's not going to deteriorate that rapidly unless the heat sink is badly fitted in the first place.

Similar thermal compound is used in computers and amplifiers. I've got amplifiers over 50 years old that have never required such maintenance.

I've found most Americans that can do things have gained their skills in the military. If a part fails then it gets analysed for cause of failure and remedial action taken. If that part overheated because of insufficient heatsink compound which had dried out as a result and was no longer functioning as thermal transfer paste, they decide that it must all be prone to drying out and therefore needs periodic renewal.
This periodic interval is usually set at a ridiculously frequent time but would you fancy being in an aircraft and wondering if the heatsink compound on the vital control systems had been renewed?

While that's true to a point, if there is enough on there to start with, it won't dry out in normal service conditions. However, with military kit it is exposed to extremes we wouldn't normally encounter, except perhaps under the bonnet of a car.
That said, 10 years would be a suitable inspect/renew interval but if it's unknown whether it has been done ever, it's best practice to do it anyway.
You're probably wondering why - i've renewed countless ignition amp modules in my time, not just Volvos but other makes that use similar Bosch items and also a few Japanese ones and the common factor in all of them was either no heatsink compuond from the factory or so little as to be useless.

As for amplifiers 50+ years old on their original heatsink compound, that's because they were built with quality components and enough heatsink compound in the first place - built to a quality level, not to a price! Similar theory applies to the compound itself, they expected the components to last and so made sure the compound would as well. Now there is built-in obsolescence and limited lifetimes so they can sell a new amplifier unit at 5-10 years old.