I dont know if I am paranoid or not but I am sick of driving my car (91 348 TS) and staring at the oil pressure gauge. It seems that once my oil temp get good and warm (aroung half just under half mark) my oil pressure sucks. At 6000 rpms I will hit 70 to 75 pounds. The manual states it should be higher. Cruising in 5th gear at 3000rpms I probably have around 50 and at idle (900rpms) the needle drops to about half way between 0 and the 35 pound mark. These numbers seem low to me and I am hoping someone can tell me what to look for or that I am crazy and just dont look at it because it is normal. Otherwise the car runs great and I am obsessed with this damned oil pressure.
I should add that sometimes when the oil is pretty warm, I barely reach 70 pounds at 6000rpms. I would like to hook a mechanical gauge up to see what the TRUE pressure is, but I do not know where to hook it.
You have essentially nothing to worry about. The motor needs about 10 PSI of oil pressure for ever 1000 RPMs to refil the bearings with oil thrown out on the last revolution. Basically as long as you have 20+ PSI with hot oil at idle and 70 PSI of oil at high RPMs, the oil flow rate out of the pump is fine. What oil are you running?
I am running 5w 40 synthetic oil, AGIP and the oil was changed last Saturday and when hot the oil level is just shy of the high mark on the stick. I just went for a nice 20 mile ride and here are my readings. Oil Temp at around 200 degrees Idle: half way between 0 and 35 (17.5?) 3000 RPMS in fifth gear: A needle width under the 70 mark. (50-60 pounds) 7000 RPMs: Just shy of the center mark of 70 pounds (give or take a pound either way) I am considering changing the sending unit to check it but hate to spend the money for nothing. Thanks
Your oil pressure is fine. Stop worrying. Drive faster! (but well within the limits of safety and political correctness)
My 308 did something similiar when I first got it. An external guage confirmed the pressure was fine. Turned out to be the oil sender.
I would like to try a sender if anyone has one to try. I would also like to try a mechanical gauge but cant figure where to pipe it in. Anyone done this?
I had an oil pressure sender go out, the new one reads 10 PSI lower than the old one. It is the nature of uncalibrated sensors.
I see the sender. Is there a place to plumb in a mechanical gauge or do you have to take the sender off and make an adapter? Thanks for the guidance.
Anyone know the trick to getting to that sender. I cannot even get my hand near the wires to spin the sender off.
Ok, I'm a somewhat of a noob when it comes to this, but a while back I was really concerned about Oil pressure as well, as my gauge was extremely inconsistent. I took some time and sniped a MAC Tools pressure tester for about $30 (picture 1). It took me SEVERAL attempts to get at that price, but I wasn't in a hurry. This set came with a number of adapters, one of which was threaded exactly as the OEM sender unit (picture 2). So I assume that the sender would be unplugged, and the analog tester would be connected in place of the sender unit. Photo 3 is my attempt at an "exploded view" of the connections involved. Photo 4 is an attempt at the closeup of the threads on the sender unit and the adapter for the tester unit. Note that the sender is an inch closer to the camera than the sender, which might make the threads look not quite the same. I never actually used this, as I ended up checking a number of other electrical issues and this problem simply went away after my "electrical cleanup," but I assume this would be the way to go about it. Can anyone verify or correct me? Photo 1: MAC oil pressure tester. Photo 2: My oil sender unit which was eventually replaced. Photo 3: Exploded view of the tester, as it would temporarily replace the sender unit. Photo 4: Close up of threads of tester and sender... leading me to believe this would be the way to go about testing. Edit: FChat giving me errors when trying to upload pictures. Reconnecting and will try again... I hope this helps and doesn't just cause further confusion...
Pics attached this time... Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Wow...thanks for the time you took to post that. If I may ask, what was your gauge doing and what do you suspect fixed it? Wanna sell that tester....lol!!!
Those two threads do not look the same to me. Your adapter looks to be an npt thread (tapered) while the sender looks like a standard thread, probably metric, maybe 10x1.0. If the sender was npt it probably wouldn't have the copper washer... I would make sure threads are the same. Jes
Agreed, I would definitely confirm before using. However, it is a particularly bad picture. The camera is about 4 inches away from the sender, and 5 to 6 inches away from the tester. It distorts the apparent perspective/scale. Not sure why it appears tapered, maybe because it is at a slight angle to camera, but once that adapter is in your hand, it definitely isn't. In any case, good point on the copper washer... and DEFINITELY a good point on confirming before use.
My oil pressure gauge would just work erratically. It would show pressure as expected, then would drop to zero for a few seconds, then pop back to where it should be for a few minutes, then drop again. This was happening at a point where I was battling all kinds of electrical gremlins. There was a rat's next of wiring from an alarm system, stereo and amp that a previous owner had put in. The wiring job was just shockingly bad. I removed all of the extra aftermarket electronics and cleaned all of the electrical connections in the systems that were playing up, and all my problems went away. As for the tester, I like having it available "just in case," so I don't really want to sell it, but more than happy to lend it out. However, if you really wanted you're own, here is the exact same one currently at $33: http://www.ebay.com/itm/NEW-MAC-TOOLS-TRANSMISSION-OIL-PRESSURE-TEST-KIT-/350546729519?pt=Motors_Automotive_Tools&vxp=mtr&hash=item519e369a2f
This may be completely off base...but... It is my understanding that there is a spring-loaded ball-type check valve in the oil return system, or in the oil pump, that (by use of the spring) relieves excess pressure, particularly at high RPMs. If that spring breaks, or weakens, then rather than provide relief from excess pressure, the valve does not allow the pressure to come up to the regulated level at idle. In other words, it works essentially opposite of how it is supposed to work (relieving most of the pressure at lower RPMs). The fix, apparently, is to replace the spring. I haven't opened mine up yet to see. I'm planning on an engine out service either later this year or early next. I'll likely go ahead and just replace the oil pump then. Can anyone substantiate this theory? Mike
If anyone is having concerns about the oil pressure in thier 348 or 355, get a mechanical gauge and test it before you throw money at it. I have been chasing a low oil pressue issue for weeks and finally broke down and got a mechanical gauge to get a true reading. Here are the results: Idle Cold (First five minutes) Elect: 65 Mechanical: 90 Warm Idle: Elect: 30 Mechanical: 60 Hot Idle (20 minutes idling) Elect: 20 Mechanical: 50-55 Give it a rev to 6K Elect: 45-50 Mechanical: 90-100 So, as others have said, use these gauges as a guide because I can now say they are not very accurate, at least mine is not. One other tip. If you buy a mechanical oil pressure tester, you will need an adapter to thread it in to the oil filter housing. The adapter has to be 18MM x 1.5 thread pitch. The one that comes in the MAC kit looks close but is NPT and will strip the threads on your aluminum oil filter housing. Hope this helps someone out there
Very interesting... It's horrible that the electric gauge is so far off base. Thanks for investigating.
Well, to be fair, I may have a bad sender. I just ordered one and will know in the next few days. If the new sender gives me the same readings, then these gauges are WAY off. The difference was 20-30 pounds at any given point. That is HUGE. At least I know the TRUE oil pressure but I cant understand why they would be that far off. Crazy
I have had senders fail before in other cars. Hopefully the new sender will give you a true reading-make sure you let us know the outcome.
