Oil Pressure Gauge 2.1@500RPM

[rinconmann]

Working on my 94 this weekend I noticed driving over 1000rpm I was over 3.0 on my oil pressure gauge then when at idle 500rpm it would only go to 2.1. The 3.0 is normal at freeway speeds but seems to me the 2.1 is a little high.

I’ve read other posts on the matter but still am unsure if I’m being too picky. Is it even an issue to take the time and replace the oil pressure sender and seal ring? Not sure of the lower harness age but if it were harness issues I should not see fluctuations from 2.1 to 3.0 as it would be at 3.0 or zero I’d think.

See the dash pictures. Using liquid moly 20-50 I recall but not sure as I write this. Any opinions are welcome.

 

[TimL]

this is totally normal and nothing to worry about

 

[gsxr]

I agree with TimL, 2.1 bar at idle is probably normal with 20W-50, in CA winter temps (60-70°F highs). In summer when the oil is hotter I'd expect that to drop below 2 bar.

Usually, an old pressure sender reads lower than actual. Wouldn't hurt to check what sender is installed, there's generally a date code but it may be difficult to read. If 30 years old, a new sender wouldn't hurt (OE or OEM Hella/VDO only) but may not change the reading. I'd ignore it as long as there are no other oddities with the pressure readings.

 

[rinconmann]

Thank you Guys,

Oddly enough the more I drove it (to the smog shop as I am in CA) the reading went down. After I wrote the post and drove off it was 3.0 at idle on the way to the smog shop and upon getting back (it failed horribly) it was down to 1.5. Not sure why more driving would bring the oil pressure down but there it is so for now I'm moving onto the "other issues". Thanks

 

[szvook]

The lowered oil pressure after driving is normal, since the engine oil heats up as you drive and gets thinner, thus will flow more freely resulting in a lower oil pressure. Driving in hot weather will lower your pressure a bit more at idle.

 

[gsxr]

Oddly enough the more I drove it (to the smog shop as I am in CA) the reading went down. After I wrote the post and drove off it was 3.0 at idle on the way to the smog shop and upon getting back (it failed horribly) it was down to 1.5. Not sure why more driving would bring the oil pressure down but there it is so for now I'm moving onto the "other issues". Thanks

This is also normal. Engine coolant temp usually comes up to normal (80°C+) quite rapidly, within 5-10 mins tops, if the thermostat is good. However, oil temp takes a LOT longer to reach similar levels. Sounds like once the engine oil was at normal temp, your pressure readings also dropped to normal/expected as well. "All good", as the kids say. (Edit - Steve was posting at the same time I was, lol!)

Now, what's this about failing smog? Can you post the numbers from the test? Did you drive with the engine RPM's at 3-4k for at least 5 mins before arriving at the test facility? This is needed to fully heat the catalysts... otherwise HC numbers may be too high.

 

[szvook]

Factory cats do take a bit to fully warm up. When I had factory cats, I always took my whip on the freeway to maintain a higher RPM range before getting the smog test. Even now with 200 cell and smaller size cats, I still do the same routine.

 

[gerryvz]

I've seen hot oil in engines go as low as 1 bar on the pressure gauge -- nothing to worry about. When you're at 1 and below, then it's time for an oil pressure sender replacement. We have a HOW-TO on that. Factory MB or VDO only. No Chinese or other aftermarket garbage senders.

 

[szvook]

@rinconmann Since you’re a bit up north (in cooler weather than me in LA), with your oil grade you should not see your oil pressure go lower than 1.25 bar on hot days at idle. I’m running Motul 300V Competition 15w-50 oil and on hot days, my oil pressure never dropped lower than 1.25 bar at idle. But that also depends on the coolant temperature. If your coolant temperature is high, your oil pressure will be lower at idle. Once the coolant temperature drops (like after driving a bit), the oil pressure will come up at idle, even on hot days.

 

[rinconmann]

I'm going to chill on the Oil Pressure since it seems to get to normal when the engine warmed. I am in Ventura CA and it was cooler that day around 64 F so I think it was unusual. I have not been driving the car much so after the below work I will run it hot before trying again. I cleared my check engine light but it came back after the SMOG check so something is up. Since @gsxr asked about the smog thing here is a shot at the smog shop showing it at 1000 HC and I saw it myself go up to 3000 but was not fast enough with the shot being a bit shocked! Mind you just in Aug of 2024 I passed smog (for the prior year since I waited so long) and it was 130 HC at 2500 RPM. The car has never failed smog until now. I am going to do the R & R (fix and replace anything) and air slit mods on the DC's, change seals and insulators replace my plugs and gap them to 1.0 mm, check leaks on the cam solenoids since I have never had this done since I have had the car for 24 years. I do have a small oil leak most likely with the front crankshaft seal leak I posted about in 2020 but since it stopped leaking I left it alone. So hoping for the best as in CA I have to pass smog and have some ability to repair up to a point.

 

[gsxr]

The misfiring (from distributor cap issues) was almost certainly the cause of the high HC's. Cure the misfire, and HC should come back down to normal. Still need to get the catalysts nice & hot before testing though, to achieve the low measurements required by CARB.