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

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    Thank you Chris! Much appreciated.

    I wouldn't say the sensor is 'blocking' oil flow, but it's definitely in the path. When I was installing it, the thought crossed my mind, but I figured:

    1) The sensor is purposely long so it sits in the flow of oil.
    2) Most sensors from other brands are the same. If they are shorter, it's not by a lot, and the shorter ones are usually fatter.
    3) Oil doesn't have to flow through that machined channel. It can be in any portion of that opening/cavity. Keep in mind that the side pictured is the oil filter side, and the opening for the oil filter is a recessed cavity as well.
    4) Because of the open cavities in both the sandwich plate and the front of the oil filter, it seems like there is plenty of room for the oil to flow into the filter. The sensor several millimeters past where the AN fitting meets the plate, the oil can flow behind the sensor, and more importantly it can go in front of the sensor and fill up the rest of that open cavity.

    Is it perfect or ideal? Probably not, but I don't believe that it's a major problem. I very well could be wrong though; I frequently am!

    I forgot to mention in my post that when I changed the oil during the oil cooler install, I had departed from my previous Rotella T6 5w40 oil. I had that around because I use it in my Subaru, and it's cheap, so I had run it temporarily in the M20, but I always thought it was too thin, especially for track use. I switched over to Redline 15w50. That alone raised my oil pressure a good 10-15*. I probably should have tried T6 again to see if the oil cooler alone changed my pressure at all.

    On the street I've only been able to get the oil temp up to about 190-200, and at that temp my idle is at about 33-35psi. It was previously about 21-23psi with Rotella T6, but it would also get up to 225* on the street easily.


      At 190-200 *F your oil pressure is at 30psi+ idling? That doesn't seem quite right.
      I'm using Rotella 15w40 and at operating temperature my oil pressure is around 7-10psi. (M20 turbo)

      It's also hard for me to surpass 220*F oil temp unless I'm beating on the car repeatedly - and this is with the addition of a turbine. I also have the same sized cooler you (behind the grilles)with a thermostat. I average around 190*F cruising/freeway/whatever.
      VDO gauges.

      I wonder what's going on here.
      Last edited by ak-; 08-13-2017, 06:42 AM.

      1991 325iS turbo


        Yes. Where is your sensor located? Yours sounds very low. I think 15-25 is more normal.

        Even with my old stock motor my idle was over 20psi with T6.

        I should also mention that my idle is about 950-1000 rpm due to the 8lb flywheel and big cam. I don't know if that bumps it up a few psi. I've seen M20's idle as low as 650-700.


          Right, my M20 idles at 650-700. The oil light triggers at 7psi iirc, and normal is around 8 to 10psi when fully warm (I strongly believe this which is causing my concern). I know its not 15psi for certain (too high). A higher idle will definitely bump it up though - the average is usually 10psi per 1000RPM.
          My sensors are remote in a sandwich plate with maybe 10" of SS lines coming from the stock oil dist. housing. Two years ago I had the sensors on the sandwich plate on the block though with the same readings.

          I still don't think your temps should go over 200*F either, especially with no thermostat. I think you're fine though and that something is up with the gauges?

          1991 325iS turbo


            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.
            Last edited by Digitalwave; 08-13-2017, 07:44 AM.


              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

              1991 325iS turbo


                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.


                  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.
                  Below the radar...


                    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):

                    This makes me think that my temp probe is similar to running the thermostatic version of the plate, and should not pose an issue.
                    Last edited by Digitalwave; 08-13-2017, 11:51 AM.


                      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.


                        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.
                        Last edited by Digitalwave; 08-13-2017, 04:12 PM.


                          Originally posted by Digitalwave View Post
                          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.

                          1991 325iS turbo


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

                            T U R B O - M 2 0 - B U I L D

                            M U S C C O O


                              Originally posted by Digitalwave View Post
                              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,
                              Below the radar...


                                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.
                                Last edited by Digitalwave; 08-14-2017, 03:46 PM.