Oil pressure

[Rex T.]

Since a lot of recent discussion regarding oil, I switched my 67 L-79 over to Shell Rotella 10W40. The only problem (maybe not a problem) is that the oil pressure stays pegged at 60 psi when I'm driving and even further until the engine warms up. Is this TOO much oil pressure? I now have access to the same oil in 10W30 viscosity. I am planning a trip to the Corvette Homecoming in Bowling Green (about a 200 mile trip, one way) in a couple of weeks and am considering changing to the lower viscosity oil in an attempt to lower the pressure. What are the toughts about this oil pressure? As always your opinions are appreciated. Thanks, Rex NCRS #8089

[Joe L.]

Re: Oil pressure

Rex-----

The 60 psi cold is ok as far as I'm concerned. However, I'd switch to the 10W30 Rotella, anyway.

[Duke W.]

Re: Oil pressure

I've used different SAE motor oil grades over the years, and the difference in absolute viscosity range between a 10W-30 and a 20W-50 is not enough to register a difference on the gage in mild to hot weather normal road driving.

It sounds to me like someone has replaced the OE 40-45 psi relief spring with a 55-60 psi spring or has installed a "high volume" oil pump, which typically are supplied with a 60 psi spring.

If you look in owners' manuals of the era you will find that any muli-grade from 10W-30 to 20W-50 is okay for "summer" temperatures and they also say it's okay to use straight SAE 30 if typical cold start ambient temperatures are over 40F, which probably covers the majority of vintage car use. A 10W on the low end is okay for cold starts down to about 0F, 10F for a 15W, and 20F for a 20W.

The industry is now recommending lower SAE viscosity ranges - typically nothing greater than 10W-30 for modern engines, primarily because there is a marginal increase in fuel economy, but at operating temperature a 10W-30 has less film strength than a 15W-40 or a 20W-50, and I am happy to sacrifice a tenth or two in MPG to have the margin of higher oil film strength. The difference in fuel mileage is so small that it takes laboratory equipment to measure, but since the OEMs are always struggling to meet CAFE requirements, a tenth here and a tenth there can make a difference between making the numbers or not and paying big fines.

Modern S-spec motor oils are biased toward fuel economy and protecting catalysts, and it's possible that these priorities have compromised engine longevity due to "thinner" oils and less robust additive packages.

Duke

[Jim T.]

Re: Oil pressure

Some new cars are using 5W20. My son just finished a 5,000 mile vacation trip through TN, IL, IA, SD, WY, CO, OK, and TX in a Honda Pilot that uses the 5W20 and it sometimes only fires on three cylinders cruising.

[Duke W.]

Re: Oil pressure

Do you think it will still be around in 40 years?

I've never seen any data on the median life of automobiles in the USA, but I bet it's no more than about 15 years on average before they go to the car heavan, but light trucks probably live longer.

Most 15 year old cars are worth no more than one-tenth of their original value, so all it takes is one major issue - like a tranmission that needs to be rebuilt or any internal engine problem, and they are not worth repairing at commercial rates, but DIYers can keep them going longer.

Same applies to even a minor accident. Insurance companies readily "total" cars if the repair estimate reaches 80 percent of wholesale value, so it doesn't take much of an accident.

The other thing that kills old cars is busting emission tests, and some states have "buy back" programs that will pay you almost what the car is worth in emissions compliant form to junk it.

So a 5W-20 may get it through a nominal 15 year/250K mile life, but I bet my old crocks will still be on the road when half the '07s are in the boneyard or already crushed.

Duke

[J M.]

Re: Oil pressure

Rex: I had the same problem as you running 15/40 Rotella, 40-45lb at idle, 70-80lb at cruise. But my problem was my own fault as I installed a HV pump because of a recommendation I shoudn't have taken. Never the less, I switched to 10/30 Rotella and my pressure is now 35-40lb at idle, 60-70lb at cruise. This will suffice until I can install the correct pump.

[Jim T.]

Re: Oil pressure

I doubt many will be around in 40 years. I gave my grandson a 87 Honda Accord over three years ago and he is still driving it. I was surprised that newer cars are using the 5W20. Have seen the series on tv about "Ice Truckers" hauling cargo across frozen lakes near the artic circle for a diamond mines operation. Have wondered how these trucks can manage lubrication in -30 to -42 temps. Frozen brakes seem to be a frequent problem.

[Clem Z.]

engine oil and cold temps

i had a uncle who was a pilot durring WW II and he flew in the frozen north and what they did was after flying they would drain the hot oil from the engine and take it into a heated area and keep it hot. when they were ready to fly again the put the hot oil back in the engines. i bet those trucker never shut off their engines like the railroad does with it's diesels,they leave them running till they need shut down for rebuild

[Duke W.]

Re: Oil pressure

Like Clem said, they probably never shut those engines down except for maintenance, and they also probably have electric engine heaters and battery blankets as do most cars in arctic climates. When I was at Grand Forks AFB the BOQ parking lot electrical had outlets at every stall to plug in your car.

I recall some winter drives across Montana and the Dakotas many years ago. Truckers let their engines idle all night while they slept in their sleeper cabs, and Ow-30 is probably very popular in arctic climates, now. I can't remember what I used back then, but I think there was a 5W-30 available in the early seventies.

Arctic conditions provide some real challenges for lubrication engineers - like the North Slope oil drilling operations. I know Chevron has some whazzo hydraulic fluids that have a very high viscosity index. Of course the price is very high, too, compared to conventional hydraulic fluids.

I'm not at all comfortable with the 5W-20 recommendation for some new cars. I think it's okay for mild climates, but if I lived in a real hot climate I would probably use 10W-30 and take the faction of a MPG fuel economy hit.

GM Electromotive Divison (now called Electomotive Diesel under it's new owners) two-stroke locomotive engines just use straight water (maybe with a corrosion inhibitor) as coolant because the design of the power assemblies allows some leakage into the cylinders and antifreeze causes a real mess. So in subfreezing weather they have to let them idle when parked. If the engine shuts down an automatic system dumps the water. I think GM 645 and 710 engines use about a gallon per hour per cylinder (12 or 16 cylinders depending on model), and a fuel truck visits them every few days to keep the fuel tank topped off.

But this practice costs the railroads a lot of money, so some locomotives are now equipped with a small diesel engines to keep the prime mover's 300 gallons of coolant and 200 gallons of oil warm while its shut down. And I think the new GE four-stroke GEVO engine may now use antifreeze.

Duke

[Larry L.]

Re: Oil pressure

What I do with oil pumps before I install them in an engine.
I built a fixture that allows me to run an oil pump on a drill press at low speed with the pump stuck in a plastic butter container. A known accurate gauge is used to read the pump outlet pressure and you can see the oil flowing from the regulator. You can easily change the pressure by changing springs or shimming a spring. Don't stretch on.

There is also a problem with some high volume pumps and that is the clearance is too small between the regulator exit and the pan. With cold oil the regulator port is effectively restricted. I use clay on end of pump and do a fit check. I remove some material from pump housing (bottom) to give me at least a 1/4" between pump housing and pan.

With 10W30 The pressure is set to 55 lb at room temperature (cold oil) at 600 RPM. The hot oil pressure with 15W40 Rotela is about 35 lb.

Too much oil pressue is as bad as not enough. It easy to test and well woth the effort because dropping the pan and fooling with the spring is just to much trouble - unless you like to punish yourself.