Home » Public Forums » GMCnet » [GMCnet] Fluctuating Oil Gauge Readings
| Re: [GMCnet] Fluctuating Oil Gauge Readings [message #189698 is a reply to message #189620] |
Fri, 09 November 2012 00:36   |
 |
John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
Karma:
|
Senior Member |
|
|
Hi Keith:
An interesting thing about the OLDS engine is that the oil pressure sending unit is tapped at the low pressure end of oil Galleries, rather than tapped at the high pressure side of the Galleries. (Farthest away from the oil pump.) This means that you will SEE more pressure fluctuations with temperature. (As others have said fluctuations with speed and temperature are normal)
In my experience this is actually quite uncommon. Most of the engines I've worked with have their oil pressure sending units tapped on the downstream side of the oil filter where the oil enters the oil galleries. (Chevy Ford, and Chrysler V8s)
The Olds oil circuit is from the pump to cooler to filter to oil galleries (Left, Right, Main, and Cam Bearings)then the oil pressure tap. This means that the oil pressure your reading, is actually after all of the volume "leaks" of the bearings, lifters, valve train and the pressure losses of the oil passages themselves. When the engine warms up, clearances open up a bit and increases the "leaks", hence the significant and visible pressure drop at the end of the line.
Here is a flow diagram from the manual.
http://www.gmcmhphotos.com/photos/discussion-photos/p46304-oil-passages.html
When the oil pressure tap is at the oil filter these pressure drops are not as evident because the oil pump actually bypasses a certain amount of oil as the pressure relief valve opens and dumps the oil back to the oil pan. (Less so when the oil warms up and only to the capacity of the oil pump) As the needs of the engine increase, the oil pump will dump less and will make up the difference and you will see less of the fluctuations on the pressure gauge. You will find that the needles of these engines will not move as much. (More Stable) Most gauges in many vehicles are also designed to respond slower to eliminate the pulsing that you might be seeing and to simply give an indication of the oil pressure. ( The same as the Gas gauge is slowed down significantly so it does not annoyingly indicate the sloshing of the fuel in the tank. ) The reality is, very few people want to know the intimate details of the engine and indications are telling enough. The oil pressure trends over the last 3 to 10 seconds is usually plenty enough information for most people.
A hot engine that idles at 500 to 700 RMP results in the oil pump only turning at 250 to 350 RPM . The pump does not move a lot of oil and, a lot of oil leaks past the clearances. The pressure on the end of a gallery such as our 455 can actually be be quite low and still be sufficient for the needs of the engine. Especially if it increases when the engine warms up. If the other engines show that low a pressure at the pump there may actually be nothing at the end of the gallery
When I rebuilt my engine, I put in a Melling High Volume Oil pump. I set up an pressure gauge and primed the engine with this drive and a hand drill. It really loaded the drill and the oil pump dumped oil flow at 50 PSI When the engine gets warm pressure does drop a bit at idle but stays very even above idle.
Gauge set up
http://www.gmcmhphotos.com/photos/discussion-photos/p46316-pressure-guage-setup.html
Adaptor for priming
http://www.gmcmhphotos.com/photos/discussion-photos/p46310-pump-prime-drive.html
Priming with drill
http://www.gmcmhphotos.com/photos/discussion-photos/p46313-driving-oil-pump.html
Resulting Pressure
http://www.gmcmhphotos.com/photos/discussion-photos/p46307-oil-pump-dumps.html
Best Regards
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
|
|
|
|
Current Time: Mon May 06 22:44:54 CDT 2024
Total time taken to generate the page: 0.00901 seconds
|
GMCforum
Search
Help
Register
Login
Home
