Oil pressure relief, oil cooler, and accusump interaction Options

[Seabird]

Good morning everyone. I am in the process of upgrading my oil system. This is on my dedicated track 914. The upgrades include remote oil cooler, accusump, and CB Maxi oil pump.

In my research for installing the accusump it seems like there are two places that are recommended, in the cooler return line with a check valve and direct to the block. I did not want to use the sandwich plate adapter so I opted for the block option. Simpler with less seals to fail.

As I looked into the workings of the type IV oil system I found a potential problem with both these locations; the oil relief valve on the front of the engine. VW used this valve to bypass the cooler when the oil is thick. But this also means the cooler is bypassed when the oil pressure is high. Does the use of an oil accumulator negate the oil cooler system by maintaining oil pressure?

While on the straights the pump could potentially make 50-60 psi of oil pressure. (the 30mm pump that was in the engine produces those pressures much of a 20 min session) At those oil pressures the cooler will be bypassed based on what I know of the relief valve (bypassing cooler at 60psi, partially open at 35 psi, and sealed at 12psi). The accusump will also build up to that pressure. When I go to brakes and the revs drop the accusump will start pushing back and keep the pressure up till the differential is corrected. If I am back on to the next straight in that time then the pump starts building the pressure again.

Options:

1. Am I making a mountain out of a mole hill? Leave it alone.

2. Plug that relief valve so it stays closed and let the oil cooler thermostat bypass the oil when its cold. This is a pre 76 case so there is the secondary relief valve by cylinder 1. Might be able just to invert the piston so the bypass grove is below the bypass passages.

3. There is also the high pressure pistons sold by pelican parts and others. Does this just shift the bypass window to a higher pressure range?

I would love to hear people's thoughts on this.

Miguel

[Jetsetsurfshop]

I ran 240-250 in the afternoon sessions. Did an extra cool down lap and got back to 230 before the pits. It was hot out there, wow!
If the sessions were any longer, a front cooler would be the answer.
I see a cool 914 in the background in post #41. (behind the ugly dually)
(IMG:style_emoticons/default/biggrin.gif)

[Seabird]

I ran 240-250 in the afternoon sessions. Did an extra cool down lap and got back to 230 before the pits. It was hot out there, wow!
If the sessions were any longer, a front cooler would be the answer.
I see a cool 914 in the background in post #41. (behind the ugly dually)
(IMG:style_emoticons/default/biggrin.gif)

Yeah (IMG:style_emoticons/default/wink.gif) I picked that one for you.

So you think we could see a heat soaking issue where eventually the cooler can't keep up?

Miguel

[ThePaintedMan]

So you think we could see a heat soaking issue where eventually the cooler can't keep up?

Miguel

Miguel,
I think that's always been the consensus with any aircooled engine. Since oil becomes the primary fluid involved with heat transfer, and is less thermally efficient than water, you see a longer "lag" in temperatures. I.e., it takes longer to heat up than water, but also is harder to cool back down once hot.
There are some that suggest that increasing the *volume* of oil in the engine helps with this, but in my admittedly small knowledge of fluid dynamics, that would essentially only delay the eventual point that you described - where the cooler simply can't keep up with the temps.
Which is why everyone just ends up going to a bigger cooler, or making the existing cooler work more efficiently (exposing it to cooler air, faster air, etc).

I may not belong in this conversation since I'm not an engineer, but this is my understanding of the challenges of aircooled engines. Please kick me out if I'm over my head. (IMG:style_emoticons/default/biggrin.gif)

[Seabird]

I may not belong in this conversation since I'm not an engineer, but this is my understanding of the challenges of aircooled engines. Please kick me out if I'm over my head. (IMG:style_emoticons/default/biggrin.gif)

No your on point. I am a stubborn one though (IMG:style_emoticons/default/headbang.gif)

There is a certain amount of energy being transferred into the oil from friction and heat. Then their is a certain amount of energy being transferred out of the oil through heat when it passes the cooler. It is possible that the cooler's ability to transfer heat out is less then what is being generated by our engines.

If someone wanted to they could work out just how much energy was being generated by the engine. well a very close approximation. Oil temp delta in a fixed amount of time while under track conditions would do it. Then someone could select a cooler that had something like 1.5 times the heat exchange rate, maybe 2 times to be safe. There are some little details there that are missing; the exchange rate based on air flow. But that's also fairly easy to work out.

By the way its been a long time since I have actually worked as an engineer. I can honestly say I was educated as an engineer but not much beyond that these days. (IMG:style_emoticons/default/biggrin.gif)