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I usually run Mobil-1 Syn 15w-50 w K/N filter and I recently changed (yesterday) to 5w-30 Mobil 1 syn. After the change my oil pressure (autometer) dropped more than 10psi's   . Everything is the same..fill level..same type filter everything.. but the oil pressure is lower.. I think I might be swithching back to 15w-50.
Anyone have a detailed reasoning.
Eric
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thicker oil flows slower than a thin oil, but the oil pump moves a constant volume. What happens is the pump always moves a constant volume of oil for each revolution. Becasue the thicker oil flows slower but the pump moves a constant ammount of oil for each revolution the thicker oil has to be pumped at a high pressure to move the same volume of thick oil as it does if it were a thin oil.
Just incase the oil pressure gets too high, there is a relief vavle built into most engine oil systems (usually inside the pump) to keep the pressure from getting dangerously high.
There is also a relief vavle inside most oil filters to pretect the filter canister from rupturing due to high oil pressure. What this vavle does is allow oil to bypass the filter element and go directly to the engine. The idea here is that if the pressure in the filter gets that high then there must be a clogged filter so dirty oil is better than no oil.
I feel sorry for the people who don't drink. When they wake up in the morning, thats the best they're going to feel all day - former President Lyndon B. Johnson
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well at crusing speed with 15w-50 I was just a hair below 50psi.. now with 5w-30 I'm a hair above 25psi..  I think I will switching back to 15w50.. I just like the reassurance of stronger oil pressure.. eric
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There is a higher pressure because the oil is not flowing as well; if it isn't flowing as well, it would lead you to believe that your parts aren't getting lubricated as well. I would stay with the 5w30 myself.
Matt
2000 SVT Toreador
#1210 of 2150
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I run 5w-30 myself. I don't seem to have any problems, but why don't you try 10w-40 for a compromise?
Totally sold out for a 90 GT vert.... 1/4 mile is almost the same as my modded svt w/n2o was...
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IM not sure how many miles you have, but switching form a higer weight to a liger weight could "locate" leaks that the thicker oil could not squeez out of. Thus lowering your oil pressure....Take a look at any visible sign of leakage....if there is none then its just the presure drop of the lighter oil...If you find some, replace the gasket and you should be ok.
Roz
3.0 SVT hybrid...all the fixens...Track/Race ready very soon!!!!!! 20,000 + miles
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b0x @dm1n
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The reason the PSI dropped is because the 5w-30 flows better. All you are going to do with the heavy oil is blow seals and gaskets. The higher PSI is because it's not flowing nearly as well. A PSI that high is similar to someone having a blockage. Sorry but you are just plain stupid for running such a thick oil and I'm sure your gas milage is hurting to prove it! Higher PSI is bad, but so is 0!
-Andy
Andy W.
The problem with America is stupidity.
I'm not saying there should be a capital punishment
for stupidity, but why don't we just take the safety
labels off of everything and let the problem solve itself?
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no my gas mileage hasn't changed with the 15w50, and I have no leaks as well.. just recently had my rear main seal changed and checked for other leaks as well..
eric
um oh yea.. I live in Florida so it IS ok to run a thicker oil.
Thanks JSMITH for an actual Educated answer.
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Originally posted by xdouble:
There is a higher pressure because the oil is not flowing as well; if it isn't flowing as well, it would lead you to believe that your parts aren't getting lubricated as well. I would stay with the 5w30 myself.
Exactly!
Higher oil pressure DOES NOT mean better oil flow, volume or protection.
In this case it just means more resistance to being able to flow. Which is a bad thing!
Especially at startup and high rpms. Those are 2 areas I definitely would not want degraded oiling ability and protection.
Then top it off with the extra parasitic drag of running the nearly twice as thick oil!!!
2000 SVT #674
13.47 @ 102 - All Motor!
It was not broke; Yet I fixed it anyway.
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Originally posted by DemonSVT:
Higher oil pressure DOES NOT mean better oil flow, volume or protection.
In this case it just means more resistance to being able to flow. Which is a bad thing!
Especially at startup and high rpms. Those are 2 areas I definitely would not want degraded oiling ability and protection.
Then top it off with the extra parasitic drag of running the nearly twice as thick oil!!!
I agree. The engine was designed to operate with a 5W-30 oil. That means that the oil galleries that provide a flow path for the pressurized oil to get to all the places it needs to be, the oiling holes in the bearings and the oil cleanances of the bearings are all designed with respect to the flow rates and characteristicts of a 5W-30 oil not 15W-50.
Traditionally it has been accepted that a thicker oil provides a stronger film. Well that is usually true, but a thicker oil needs to have a thicker film than a thinner oil in order to offer its higher film strength. The engine's oil cleanances within the bearings are as such to provide a maximum film strength from a thin oil and the clearances may be insufficent to reap the full benifits of the higher film strength ofered by the thicker oil.
making that extra oil pressure takes power which robs the engine of power that could otherwise be used to turn the crankshaft. The thicker oil also has a higher flow friction, in other words a shaft supoported in a bearing lubricated by a thick oil will be harder to turn than the same shaft and bearing lubricated by a thin oil.
I'd like to see someone test this theory by taking their car to a dyno: With the engine fully warmed up do a run with the 15W-50 oil. Then change the oil to a 5W-30 oil, warm the engine up again to get the oil up to temperature and do another dyno run. I am confident that there will be a definate increase in horsepower with the 5W-30 oil over the 15W-50.
I feel sorry for the people who don't drink. When they wake up in the morning, thats the best they're going to feel all day - former President Lyndon B. Johnson
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