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Oil Temp Problem

 
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 1065
Location: Maysville, Colorado

PostPosted: Wed Aug 25, 2021 6:45 am    Post subject: Oil Temp Problem Reply with quote

In the track car the motor oil has been running 220F for the last two years. Last time out it pegged at over 250F. I have changed the oil and dismantled and cleaned out the entire system and cut the oil filter open and inspected it. No sign of a problem, now runs fine with 6 bar at idle. They only change I made to the car was that I changed our the 4 speed for a 5 speed. It was running strong and I could really tell the difference of the 4.11 vs 3.88 axle('78 US).

But, I am wondering if the tranny could be just dragging enough to over heat the motor oil?. Before I put it in it was turning quite freely, as easily as the 4 speed, and I also drained it and then put in some diesel, turned the input shaft about 200 turns and rolled the transmission around to try to clean it out. Then I put in to Redline MTL before running it. I made an illegal test cruise around the neighborhood for about 3-4 miles before taking it to the track. Ideas?
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Poco a Poco, #033 '78 Vintage racer, SCCA Dp-81
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Cedric  



Joined: 27 Aug 2004
Posts: 2202
Location: Sweden

PostPosted: Wed Aug 25, 2021 4:22 pm    Post subject: Re: Oil Temp Problem Reply with quote

MikeJinCO wrote:
In the track car the motor oil has been running 220F for the last two years. Last time out it pegged at over 250F. I have changed the oil and dismantled and cleaned out the entire system and cut the oil filter open and inspected it. No sign of a problem, now runs fine with 6 bar at idle. They only change I made to the car was that I changed our the 4 speed for a 5 speed. It was running strong and I could really tell the difference of the 4.11 vs 3.88 axle('78 US).

But, I am wondering if the tranny could be just dragging enough to over heat the motor oil?. Before I put it in it was turning quite freely, as easily as the 4 speed, and I also drained it and then put in some diesel, turned the input shaft about 200 turns and rolled the transmission around to try to clean it out. Then I put in to Redline MTL before running it. I made an illegal test cruise around the neighborhood for about 3-4 miles before taking it to the track. Ideas?


Do you run a thermostat for the oil cooler or is it always fully open? Only reason i can think of is that you spend more time at higher rpms due to the tighter gearing, higher rpm definitely increases the oil temp. Though that seems like a very big difference.

If that much heat was because of potential gear box drag it would feel like you had the parking brake engaged, and it would melt pretty quickly.
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D Hook  



Joined: 02 Nov 2002
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Location: Omaha, NE

PostPosted: Wed Aug 25, 2021 7:53 pm    Post subject: Reply with quote

6 bar at idle is 87 psi. That seems a bit high.
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924RACR  



Joined: 29 Jul 2001
Posts: 8471
Location: Royal Oak, MI, USA

PostPosted: Wed Aug 25, 2021 9:38 pm    Post subject: Reply with quote

Yeah, shorter gears will make more heat.

I'm guessing that 6 bar is cold idle, not warm idle...

250 isn't too bad if you're running synthetic; not ideal but still entirely workable if dino oil. 220 is actually at the bottom range for optimal power...
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 1065
Location: Maysville, Colorado

PostPosted: Wed Aug 25, 2021 10:49 pm    Post subject: Reply with quote

Thanks for the input, it starts me thinking about this in different ways. I originally had an oil thermostat, but removed it a few years ago as when I looked at how it worked the one I had really restricted the flow. Another example that if you try to do it the cheap way($75 vs $200 for a good one) you end up paying for it twice. That and a larger cooler(8x10 I think) reduced the temp from 250+ to 220. I have 6 bar at cold start up and idle with oil temps in the 100-150 range. It typically runs at the 6 range. I increase the idle to 1200-400 when home to keep it running as the 45 Webers are not real happy idlers.

I have run Driven semi-synthetic this year. Yes the rpm picked up probably 400 to 600 everywhere, I was accelerating well when before sort of stumbling along at times, lots of difference from about 3600 to 4200 on my quite mild cam. I don't have a tire(Nitto) temp gauge, but I noticed they had picked up much more garbage so had to be quite a bit hotter. It was also 95 degrees out there. So a lot more heat in general

Another factor could be lack of cooling, I run at 5000+ ft so the cooling is dropping about 15 to 20 percent due to air density. I could use a 931 front metal to get the air vents to cooler and 951t radiator.

I've decided to put the car up on blocks, then run it in 2nd gear. Then I'll check the tranny temp with my infrared thermometer, if no problem it shouldn't heat up much just free wheeling.

The motor man and I are going to recheck and possibly reset the timing a bit as his circle track folks have significant oil heat problems with too much distributor advance.
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'77 924
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Last edited by MikeJinCO on Thu Aug 26, 2021 4:13 am; edited 2 times in total
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Cedric  



Joined: 27 Aug 2004
Posts: 2202
Location: Sweden

PostPosted: Wed Aug 25, 2021 11:24 pm    Post subject: Reply with quote

Altitude definitely affects the cooling, i worked with high altitude calibration at my previous work position and its something you can clearly see in the data.

I think before you conclude that something have changed you should run at a track where you have been before in conditions you have run before. 120degC is where a stock 924 and 931 seems to hoover around on track, at least over here.
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 1065
Location: Maysville, Colorado

PostPosted: Wed Sep 15, 2021 11:23 pm    Post subject: Reply with quote

Update. Ran it on blocks for 15 minutes and transmission not a problem. Then took it out to track last week. Temperature only 80F(morning) oil temperature never got over 210F, water at 180F. Next race weekend is Sep 25/26 temperatures will probably be 85+.
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Mike
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'77 924
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924RACR  



Joined: 29 Jul 2001
Posts: 8471
Location: Royal Oak, MI, USA

PostPosted: Thu Sep 16, 2021 3:33 am    Post subject: Reply with quote

Sounds promising!
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Vaughan Scott
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 1065
Location: Maysville, Colorado

PostPosted: Thu Sep 16, 2021 10:23 pm    Post subject: Reply with quote

I measure the temperature coming off the motor where I should measure it in the sump or returning to the sump. I drilled and tapped the drain plug but did not want to be disconnecting it all the time to change oil as it would just promote future problems. I found a good inline sensor tap but that requires enough AN plumbing changes that I wont start that trial of a project during the season. If I can get my new motor ready for next year I'll need to upgrade the cooler again from the supposedly 20,000 BTU as the oil supposedly supplies about 40% of the motor cooling.
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'77 924
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ideola  



Joined: 01 Oct 2004
Posts: 15535
Location: Woodstock IL

PostPosted: Thu Sep 16, 2021 11:52 pm    Post subject: Reply with quote

What instrument are you using to measure temps? Are you logging it or eye-balling it? Voltage variations and bad ground can wreak havoc on instruments...
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Thu Sep 16, 2021 11:56 pm    Post subject: Reply with quote

What matters most is to understand the long-term behaviour, less so one specific location vs another.

On my P2, I measure it in the tank and also coming out of the motor... but that's a different story, as the exit from the motor is on the scavenge side (dry sump), before the cooler.

On the 924, since the plumbing is different and wet sump, I measure it at the oil filter, heading to the cooler, because that was accessible. I simply drilled and threaded an already-existing boss on the oil filter remote mount, and put the sensor in there. So in my case at least the oil going into the motor wil be cooler than what I'm measuring. And since the pump is drawing from the sump, while the sump could be a little hotter it won't be much different.

In this case, I'm getting the measurement of worst-case, so I can see if the oil is at risk of breaking down.

Seems similar to your setup... and you won't be able to measure it returning to the sump, because that's the internal draining down the inside of the block.
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