a new Low Idle Pressure Only theory

[Ecomike]

OK, I have some preliminary data. I tested the oil temperature with 2 infrared sensors. One read about 10 degrees higher than the other. I also discovered that the readings were about 5 degrees higher if read at about 1/2 inch from the surface versus reading it say 6 to 8 inches from the surface. These readings were taken with the lower reading gauge at the 1/2" distance. Readings were taken in Park (P) at idle unless noted otherwise.

Oil Temp H2O Temp Oil Pressure Engine
F F PSI RPM
108 165 58 700
138 175 52 750
158 186 42 725
166 190 35 750
166 190 42 3000 (in P)
179 200 25 600 (in D)
179 200 42 2000 (in P)
187 198 31 750
187 198 39 2500 (in P)
187 198 25 600 (in D)

These tests were all in the driveway, no highway long drive data yet. Ambient was about 80 F. Oil under the valve cover right after turning the engine off was 194 F. I have a 165 F thermostat. Oil level was exactly at the full mark.

I ran into some real intersting data. Turns out my electric fan cuts on at about 175-180 F, and off at about 165 F. The water on the inlet of the radiator was reading about 200 F, but the coolant temperature on the cool side of the radiator at the fan temperature switch was running 165 to 180 F. The fan cut on at 175 to 180 F! Most of us have been under the impression that they are set at 220 F (other threads) because we were reading the other temperature gauge from the thermostat. Only makes sense that the water leaving the radiator to cool the engine (where the electric fan switch Temp sensor is located) must be cooler that the water leaving the engine, otherwise it would not cool the engine!

Also, I used the $10 infrared gauge and $25 infrared gauges (sale prices) from harbour tools. They are a great little tools for this work. The $25 one reads up to 480 F, the $10 one reads up to about 210 F max. I even got readings right at the engine/exhaust interface before it over ranged on me! Hell of a tool for finding hot spots and checking radiators, thermostats, etc.

 

[Ecomike]

What a pain. It is not posting the data the way I wrote it. So much for WYSIWYG text. Anybody know how to make this thing post a nice looking readable data table?

 

[skipc]

Oil Temp H2O Temp Oil Pressure Engine
F F PSI RPM
108 165 58 700
138 175 52 750
158 186 42 725
166 190 35 750
166 190 42 3000 (in P)
179 200 25 600 (in D)
179 200 42 2000 (in P)
187 198 31 750
187 198 39 2500 (in P)
187 198 25 600 (in D)

Don't you mean H2O temp, then Oil temp?

The numbers look great.

Skip

 

[Ecomike]

Don't you mean H2O temp, then Oil temp?

The numbers look great.

Skip

Actually sitting in the drive just idling the water heated up faster than the oil, which followed or agreed with what I had seen on the oil pressure and water temperature gauges before and during this test. They are right, no they are not backwards, SURPRISE!

Yes, the numbers do look great! The oil temps even surprised me.

At first I thought maybe I was not getting real live oil temp readings, but after doing some checking I think the oil is pumping through my 1 quart oil filter at about 8 gpm (high flow oil pump), or 32 qts per minute or 1 pint per second and the filter housing is thin so I suspect the outside housing temperature is pretty close to the inside oil temperature.

I still need to run it on the highway on a real hot day with the A/C going but the A/C is down so I will have to settle for a good highway run tommorow at 80 F ambient to push the oil temp higher.

 

[DaveKerwin]

I assume your results will be much different testing after a long drive

I wonder if less or more oil (over or under the recommended quarts) would change these numbers a lot.

 

[Ecomike]

I assume your results will be much different testing after a long drive

I wonder if less or more oil (over or under the recommended quarts) would change these numbers a lot.

I took a pair of 30 mile highway runs yesterday. Even spent part of the drive at 2,800 rpm in 3rd gear to try and superheat the oil. Ambient was only 72 F yestday. No A/C.

Highest readings I got were 203 F water/coolant temp reading at the thermostat housing and 199.8 F oil temp at the bottom side of the oil filter housing. Minimum oil pressure was 22 psi in drive at 600 rpm idle. It came back up to 25 psi at 800 rpm in park at idle. The 22 psi reading was very brief and came back up to 25 psi pretty quickly this time while sitting at idle.

I must say I am surprised at the oil temperature readings. I still don't know for sure if there is any significant measurement error or difference between the oil pan oil temperature, bearing oil temperature and the oil temperature through the filter housing that I am reading, But I suspect the bulk oil temp in the pan is no more that 5 to 10 degrees higher than what I am reading on the outside filter housing.

Seems the oil temperature is staying very close to the water/coolant thermostat housing temperature so far. Keep in mind that the water/coolant temperature exiting the radiator and entering the engine has been reading 165 to 180 F.

Unless you cross some critical oil level (like starve the oil pump) I doubt it would have much effect on the oil temp.

 

[DaveKerwin]

have you experienced the low pressure yet?

 

[Ecomike]

22 psi is the lowest I have seen since I started this thread. Last summer it got down to a minimum of 18 psi one day but I think the idle was lower then.

When I started this thread I was expecting, and hoping to find engine oil at say 220 to 250 F causing the oil pressure to drop from 58 to 22 psi after the long highway run. So far I have not seen anything over 199.8 F for the oil temp and oil pressure at 22 psi minimum at 600 rpm idle in drive while at 199.8F oil temp and 202 F water temp.

So far my theory is shot to hell, at least on my jeep!

Of course if I did add an oil cooler in front of the radiator and condensor, and kept the oil temp down to 175 F I could get and hold 31 psi at 600 rpm in idle according to the data I gathered with my current oil blend, but many say that the oil needs to get hotter to drive off any water condensation.

Keep in mind I am already running 20W50 plus a quart of Lucas.