Half-Life | '91 DS 318iS Slicktop | Track & Weekend Warrior

[potatomash]

9-10psi on the gauge when cars off..? Probably been asked before but are you sure your gauge is correct? It's paired with the right sensor etc..?

[Digitalwave]

Very nice build and documentation! Attention to detail and execution are great!

Sub'd, and looking forward to the ongoing evolution.

Thanks Brian!

[Brian697]

Very nice build and documentation! Attention to detail and execution are great!

Sub'd, and looking forward to the ongoing evolution.

[Digitalwave]

Good news! The track day went off without a hitch yesterday.

The car felt great overall and it was nice to be back on the track after several months away.

I had no oil pressure issues. Water temp was perfect, right around 185-188*F all day. I still have minor fuel starvation when the tank gets below 3/8s full or so (smaller 318 tank). I will need a surge tank at some point. For now I am just going to keep the tank filled to around 3/4. The breather line on the tranny worked great, and I didn't have any oil seeping down the tranny like last time.

Oil temps averaged 220-225*F. The max I saw was 232*F. Temps would drop back down to 185 during the cool down lap, so idle pressure in the pits was still 27-30psi (as read by my gauge which says 9-10psi when the car is off, so who knows).

My pressure never dropped below 60psi in any corners, even left-handers. The baffle and crank scraper did a good job.

Based on these temps and pressures, I am guessing I can try 5w40 or 10w40 oil next fill? What would the expected changes be, lower pressure (of which I have plenty)? Would it alter the temps much? On the SpecE30 forums I've read that lighter oil in some cases can lower temps since thinner oil sheds heat better.

EDIT: I just popped a new thread for the oil viscosity in the M20 forum. Feel free to reply here or there: http://r3vlimited.com/board/showthread.php?p=4816528

[Digitalwave]

Thanks for all the feedback.

I drove the car for about 45 minutes today just to do some final checks before the track day tomorrow. The tranny vent is not dripping anymore with the breather hose installed.

The oil temp seems pretty good to me. It hit 155-160 within a handful of blocks from my shop. 160 to 180 took about 10 minutes after that of cruising around. After that temps stayed right at 185-190 no matter what I was doing on the road. I did some 2nd-3rd-4th gear pulls, but none really back-to-back, as well as some low RPM cruising and idling and it stayed in the 185-190 the rest of the drive once it hit that temp. I'm expecting 210-225 range on the track, which is right where I'd like it to be.

My oil pump and pressure does seem pretty strong, but remember that this is not a stock, 200k mile M20. I'm guessing it has a new oil pump and the motor has 10-15k miles on it. I've always had greater than 10psi/1k rpm even when the car was running 5w40 Rotella T6 and the motor had no oil cooler at all. Pressure is now approx. 8-10 psi higher across the board than it was with the Rotella, after switching to the 15w50 Redline and installing the cooler, which dropped temps 20*+. That seems pretty normal to me.

Water temps are solid at 185-190* F.

For now I think I will keep the oil cooler taped off when the car isn't on the track. I'll consider switching to a thermostatic sandwich plate, but I don't think it's going to be a big deal. I figured I'd be running 15w50 year around in Florida, but if my temps stay down I could see running something thinner when it cools off from December to March.

[UNHCLL]

Just know that there is room for oil to flow behind it and the opening to the front from where the port opens up is bigger than it looks in that photo.

My oil was still reaching 180* F minimum, probably closer to 195* F on the street and that was without getting on it much, just cruising around.

Cool, the photo does make it look like it's blocking substantially more of the passage.

My S14 runs 180-195 on the street, which is where it should be running, also using Redline 15W50. Track use will climb to 220.
I wouldn't worry too much about 220-230 temps on track.

Have fun,
-Chris

[potatomash]

Just for more stats, mine idles pretty bang on 1050rpm and oil pressure is about 20psi

[ak-]

My oil was still reaching 180* F minimum, probably closer to 195* F on the street and that was without getting on it much, just cruising around.

This is good :p
Not sure if I mentioned it in previous pages, but I do love your car.

[Digitalwave]

I don't think the thermistor is blocking as much as you guys think, but I do see your point. Just know that there is room for oil to flow behind it and the opening to the front from where the port opens up is bigger than it looks in that photo. I think it would be within 20% of the way the thermostatic sandwich plate is designed after looking at those flow models. I also think Mishimoto probably planned for this when they put 2x NPT ports on the block for additional sensors. Oil temp and oil pressure are probably the 2 most popular gauges, followed by turbo feed lines.

I don't doubt part of the higher pressure is because the temps are cooler now, but wasn't that the whole point of me installing the oil cooler to begin with?

Remember that this a track car and only driven on the street when going to the track. I also autocross it so keeping the oil up to temp is a concern, but idling in line is going to be the same either way since air won't be flowing through the cooler.

My oil was still reaching 180* F minimum, probably closer to 195* F on the street and that was without getting on it much, just cruising around. It did take a little longer to get there, but that is to be expected. I could always put some tape over the oil cooler when it's off the track. Keep in mind I've put 1,100 miles on this car since May 2016 when I got it, lol.

[pandaboo911]

That thermistor does cut the return port area in half looking at your pictures. The thermostat shaft on the other hand is in the middle of the return port and oil can flow around, where yours is filling the width of the port and forces the oil to do a 90* turn.

Your oil pressure is probably high because you got a non thermostatic plate and your oil isn't coming up to temp. Try checking pressure immediately after pulling off track.. A good thermostat will fail open anyway so running one is never a bad idea especially if you run your car in varying conditions.

you could easily remove it and put a plug just to test.

[Digitalwave]

Thanks for the feedback re: the oil pressure. Yes, I have suspected as well that the oil pump on this motor was replaced when it was built (it's still a 2.5l though).

If I am understanding the diagram, the return from the cooler (the top oil line in this photo) has to pass over a shaft for the thermostat. That would essentially be the same as me having the temperature probe, no?

Oil enters the plate from the engine block side and flows out of the bottom port (where my pressure sensor is, remotely mounted via a -4AN line). It returns into the top port (where my temperature sensor is) and then into the oil filter, then returning to the motor via the hollow bolt. The thermostat version works the same way, except the return port is mostly blocked when the thermostat is closed. When the thermostat opens, the oil can flow freely through the oil cooler, but it's passing over the thin shaft of the thermostat when it reenters the sandwich plate.

Here is a picture of the thermostat. The silver shaft that oil passes over when the thermostat is open seems fairly similar in size to the temp probe:




And here is another view of when the thermostat is closed:



Full thermostat assembly (link, it's a huge photo): https://i0.wp.com/engineering.mishim...Exploded-1.jpg


This makes me think that my temp probe is similar to running the thermostatic version of the plate, and should not pose an issue.

[UNHCLL]

Just food for thought - this is their thermostatic version, but in principle, once the thermostat is open it's functioning no differently than your current arrangement.





RE: Oil pressures - your idle pressure seems strong, but not out of line with Redline 15W50. I suspect the oil pump was rebuilt or replaced when the 2.8l engine was built.

[Digitalwave]

Yeah, thanks for that. Makes me feel a bit better. I don't doubt at all that my gauge reads off, but I can at least see that I gain at least 10psi per 1,000 RPMs and it's a reference point for comparison. With my crank scraper and baffled pan I hope to see the pressures stay up on the track.

I did more research and it does seem like people either idle close to 10psi or over 20psi. Not sure what makes the difference there. Could be a combination of oil type, temperature, brand of the gauge/sender, and the location of the sender.

Between the considerably thicker oil and lower temperatures, mine sounds about right compared to being ~22psi before when I had thinner oil and 30*+ higher temperatures. The higher idle is probably contributing 3-4psi difference as well.

I'll continue to monitor especially at the track day on Tuesday.

[ak-]

That's a bit of an odd thing with the gauge. Your pressure should lower a bit off the track though seeing that it should be at it's peak temp.

Here's some relieving info though from the Bentley Manual:



I've just never seen an M20 have pressure that high at idle so maybe I was overreacting :p

[Digitalwave]

I was just going to add that I've always doubted the accuracy of my oil pressure gauge. It's an Innovate MTX-L and it reads 10psi when the car is off. When I talked to Innovate about this, they said it was normal.

Since the gauge's sender has a resistance output it will not read zero, this will not change the unit's accuracy in it's functional range. Make sure that you have the black wires from the connectors of both the temp and pressure sensors at the back of the gauge connected to ground.

My oil pressure dummy light does not turn on at all. The ground for all the gauges is good. It's shared with the ECU ground on the front shock tower. My AEM oil pressure sensor on the Subaru reads 0psi when the car off, but it could possibly be a different type of sensor.

I use the oil pressure sensor as a point of reference, but it does seem like it's probably reading wrong. What they said about it being a resistance sensor doesn't make sense to me, but I don't know much about electronics. Let's assume it's off by 10 psi. That means my idle would have been about 12psi with Rotella, and now it's 23psi with Redline.

I'm expect it's going to read in the mid to high 20psi range after coming off the track. We will see on Tuesday.