Oil pressure relief, oil cooler, and accusump interaction Options

[Seabird]

Track Test Report:

Was back up at Sebring this weekend with my 914 facing the grueling heat of central Florida in June. Surface temp of the track was upwards of 127 deg F when I measured it at mid day after one of my sessions. It was hot.

(IMG:http://www.914world.com/bbs2/uploads_offsite/dl.dropboxusercontent.com-16683-1403626412.1.jpg)

The cooler and pressure relief kits did their jobs well.

First thing I need to mention is the error in my VDO gauge. At the end of a 25 minute session the gauge was indicating 260 degree oil temp. As soon as I arrived in my pit I measure temperatures in several locations, oil cooler fins, tuna can, crank case sump (aluminum), and oil filter. Not a single one of these approached 260*. The closest reading was found on the cooler and the oil filter and they read 220*. That's a 40 degree error, on a new gauge!!

Temps were as follows:
oil cooler 215-220 depending where it was measured
Tuna can 180
Crank case 190
Oil filter 220

The oil pressure issues I was having were solved and were probably due to installer error in setting the acussump pre-charge.

While making changes and tweaks to the oiling system I closed off the top portion of the oil cooler box and added a scoop to the bottom to try and avoid picking up exhaust wash. Additionally I added a fresh air duct from the fan in the front valance to the cooler box.

(IMG:http://www.914world.com/bbs2/uploads_offsite/dl.dropboxusercontent.com-16683-1403626415.2.jpg)

The difference between the current set up and how Chris supplies the kit on track really only came down to how quickly the oil came up to its peak temp of 220. Without the extras the temp would come up to 220 within 3-4 laps and with the extras it would take 5-6 laps. If 220 is the ideal operating temp, which some folks promote, then the extra work was in vain.

I like that I can get a little extra cooling while idling back to my pit stall.

Throughout the session I was checking my oil pressure. Better than 50 psi was observed from the start of the session till the end. Only at idle rpms while heading back to the pits did the pressures drop. With the block off sleeve in place I am certain that all the oil running through the galleys first went through the cooler.

I am very happy with the results. If I end up with a bigger motor or a 6 I may have to swap to a front mount cooler. But if it could handle a 25 min session at Sebring in June I think it can handle just about anything its going to see with me at the wheel.

I was only able to run a session an a half as I developed a fuel starvation problem on Saturday afternoon. So now there is a new problem to address but at the least I have an oiling system that is up too par. Thanks Chris!!

Miguel

[brant]

Miguel. The numbers when exposed to oil usually show higher. The dipstick gauges take a reading very close to the stock senders and usually show numbers close to the gauges unfortunately.

I think the mass of the case and insulation qualities skews the numbers some.
It's worth borrowing a dipstick gauge to confirm

[Seabird]

Miguel. The numbers when exposed to oil usually show higher. The dipstick gauges take a reading very close to the stock senders and usually show numbers close to the gauges unfortunately.

I think the mass of the case and insulation qualities skews the numbers some.
It's worth borrowing a dipstick gauge to confirm

Yep, I am with you on that. I thought the filter would be the closest externally measurable location given the thinness of the steel wall.

Chris and I discussed removing the sender and testing it in a pot of boiling water to verify the actual error. Next time I do an oil change I will work this into my evening. Not really interested in dumping $50 of fresh oil at the moment.

Thanks for the input though!

Miguel

[ThePaintedMan]

I would tend to agree. Though VDO gauges are notoriously inaccurate in all forms, your oil temps probably were higher than 220, though perhaps not 260.

The point of the fins, sump, filter, etc being exposed to air is that they should always be cooler than the oil. The principles behind heat transfer dictate that the object (fluid) with higher heat gives off that energy to the next surrounding object.

I would definitely be curious to see the difference with a dipstick thermometer though. Does anyone still make those new?

Glad you're figuring things out though Miguel. The work that you and Chris have put in is something that we're all benefiting from for sure.

[Seabird]

I would definitely be curious to see the difference with a dipstick thermometer though. Does anyone still make those new?

I guess I could put the thermal wire that came with my voltmeter down the dipstick tube. Or safety wire it to the dipstick tube. Whats the consensus on that?

Are the VDO generally off by a constant or a scalar error? Might even be a quadratic!! If I fall victim to a Diff Equ flashback just revive me with a shot of Jack and a can of PBIR. It always seemed to work in College or at least got me drunk.... (IMG:style_emoticons/default/drunk.gif)

I digress. Further testing has been requested and I will happy provide.

Miguel

[brant]

I think they are still available new.

Manley? Brand or something

[Seabird]

I think they are still available new.

Manley? Brand or something

Yeppers Mainely
At the bottom $50

[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)

[ChrisFoley]

I have an interesting anecdotal data point to add to the oil temperature discussion.
Over the weekend I was speaking with a 914 race car owner in PA who added a deep sump to his 2270 engine after a recent engine rebuild.
He claims the deep sump radiates enough heat that he barely gets to 220F oil temp now, whereas before, it often crept up past 230 on hot days.

[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)

[Jetsetsurfshop]

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

Miguel
[/quote]

Don't know. I wonder if the oil temp would of exceeded 250 degrees if there was more time in the session. That might be my operating temperature? Thinking about that Chin event coming up in July. They have that happy hour session. That would be one way to find out.
Here's a blanket question, are we worried about what a 914 engine can put up with or the oil viscosity breakdown?
Shane

[Seabird]

[quote name='Jetsetsurfshop' date='Jun 26 2014, 11:50 AM' post='2054674']
So you think we could see a heat soaking issue where eventually the cooler can't keep up?

Miguel
[/quote]

Don't know. I wonder if the oil temp would of exceeded 250 degrees if there was more time in the session. That might be my operating temperature? Thinking about that Chin event coming up in July. They have that happy hour session. That would be one way to find out.
Here's a blanket question, are we worried about what a 914 engine can put up with or the oil viscosity breakdown?
Shane
[/quote]

I guess we'll find out if there is heat soaking ;D You got that big tank too. You think I could get the full hour in with my 15 gallon?

[ChrisFoley]

You think I could get the full hour in with my 15 gallon?

My 1.8L race car gets about 9 mpg.

[stownsen914]

If you want to calibrate your gauge/sender, take them off the car and test in isolation using boiling water (210 degrees). You'll need a 12 volt power source. Dip the sender into the boiling water and see what the gauge says. It's a pretty easy way to see if your gauge/sender are at least in the ballpark of being correct.

Scott

[McMark]

Stack make great gauges. If you're gonna pull the sender, put in something quality...

[Jetsetsurfshop]

Stack make great gauges. If you're gonna pull the sender, put in something quality...

Does the stack have a recall option?

[McMark]

Their ProControl line does.
(IMG:http://www.914world.com/bbs2/uploads_offsite/www.stackltd.com-419-1404011689.1.png)