Printable Version of Topic
Click here to view this topic in its original format
914World.com _ 914World Garage _ Oil Temp vs. Oil Weight
Posted by: NJ914Guy Jun 16 2011, 07:59 AM
Can someone please set me straight on this.
Given summer time driving (70-95 degrees temps outside):
If a 914 is running 20w-50 oil vs. 10w-30 oil, I know that the 30 weight is thinner oil, but which oil would run lower oil temps?
Thanks, having a mental block moment here 
Posted by: Cap'n Krusty Jun 16 2011, 08:21 AM
"Cooler"? Neither, really. 20w50 would be THICKER than 10w30 when the engine is hot. That should give you better lubrication at elevated temperatures in an engine designed to use it. Modern engines, mostly those designed and manufactured after the early 1990s, specify thinner oils because the oil passages are much smaller and oil that is too thick can actually cause engine failure from lack of lubrication.
The Cap'n
Posted by: r_towle Jun 16 2011, 10:11 AM
to expand a little on what the Capn said....
Your oil temps will be the same no matter what weight oil you choose.
What will change at the higher temps is your oil pressure.
20w-50 will have a higher oil pressure when hot than 10w-30.
If you drive in the winter, change it back to 10w-30 or its not to easy to start and you stand a chance of blowing out a seal when its super cold outside.
Rich
Posted by: 914 shifter Jun 17 2011, 09:29 PM
at high rpm say above 4000+ our stock 914s oil pressure will bypass the stock oil cooler. so this is the universal oil temp problem that needs to be addressed by the 21st century 914 World 
Posted by: ArtechnikA Jun 18 2011, 06:39 AM
oil's 7.2 lbs/gal no matter how hot it is ...
Posted by: Joe Owensby Jun 22 2011, 07:48 AM
There are threads discussing this before. The oil cooler bypass valve is essentially a thermostat. It allows oil to bypass the cooler when the internal pressure is above a certain pressure. It was originally designed to do this with cooler oil. If the springs on the bypass valve are not correct, then a higher viscosity oil will just pass less oil through the cooler until it heats up to a higher temperature than would be rrequired on a low viscocity oil. Doing so effectively lowers the viscosity of the oil due to the higher temperature. If you look at the viscosity charts of 30 and 50 weight oils at 200 degrees, there is a significant difference, as per design. I use the 20-50 weight oils per recommendations by the "experts", but I haven't seen any real data supporting this. I wonder why the Porsche engineers specified 30 wt. For the record, the "weight" term of the oil refers to the viscoty, not the actual weight as in the previous post.
Posted by: ArtechnikA Jun 22 2011, 08:09 AM
..."weight" term of the oil refers to the visco[si]ty, not the actual weight as in the previous post.
Really?
Posted by: scott_in_nh Jun 22 2011, 09:43 AM
oil's 7.2 lbs/gal no matter how hot it is ...
Oil expands as it is heated, so if you measured out a gallon of oil at room temp and it weighted 7.2 lbs. and then heated it to 100C it would now measure something like 1.1 gallons (but still weight 7.2 lbs.) and have a lower density.
Removing the 0.1 gallon to bring the volume back to 1.0 gallons would yield a new weight of about 6.55 lbs.
Posted by: ArtechnikA Jun 22 2011, 09:50 AM
But what if it was an Imperial gallon?
But what if it was a pound of Troy ounces?
IT WAS A FRIGGIN JOKE PEOPLE !
Posted by: ripper911 Jun 22 2011, 11:50 AM
No jokes! 
Posted by: Drums66 Jun 22 2011, 01:57 PM
to expand a little on what the Capn said....
Your oil temps will be the same no matter what weight oil you choose.
What will change at the higher temps is your oil pressure
Rich
Posted by: 914 shifter Jun 22 2011, 05:45 PM
There are threads discussing this before. The oil cooler bypass valve is essentially a thermostat. It allows oil to bypass the cooler when the internal pressure is above a certain pressure. It was originally designed to do this with cooler oil. If the springs on the bypass valve are not correct, then a higher viscosity oil will just pass less oil through the cooler until it heats up to a higher temperature than would be rrequired on a low viscocity oil. Doing so effectively lowers the viscosity of the oil due to the higher temperature. If you look at the viscosity charts of 30 and 50 weight oils at 200 degrees, there is a significant difference, as per design. I use the 20-50 weight oils per recommendations by the "experts", but I haven't seen any real data supporting this. I wonder why the Porsche engineers specified 30 wt. For the record, the "weight" term of the oil refers to the viscoty, not the actual weight as in the previous post.
bradd penn has 10w 30 i think i will try it.
Posted by: Jake Raby Jun 22 2011, 08:31 PM
That engine has my clearances. With 30 weight you'll have shit for oil pressure in the summer.
We alter our clearances to favor the heavier oil. The engine you have isn't generic and the rules others play by do not apply.
For heat Vs viscosity review this. Lake Speed and I devised a chart like this for our Snake Oil products based on temperature, load and pressures for an aircooled TIV engine. This is not that chart, but it gives an idea of the relationships between heat and viscosity when related to working pressures.
Posted by: 914 shifter Jun 23 2011, 09:09 AM
That engine has my clearances. With 30 weight you'll have shit for oil pressure in the summer.
We alter our clearances to favor the heavier oil. The engine you have isn't generic and the rules others play by do not apply.
For heat Vs viscosity review this. Lake Speed and I devised a chart like this for our Snake Oil products based on temperature, load and pressures for an aircooled TIV engine. This is not that chart, but it gives an idea of the relationships between heat and viscosity when related to working pressures.
OK Jake, thank you for the info. i think i will order some snake oil from you. i see you sell it by the gallon what is the weight/viscosity ?
Posted by: ripper911 Jun 23 2011, 09:38 AM
and where can we get it? Snake oil that is.
Powered by Invision Power Board (http://www.invisionboard.com)
© Invision Power Services (http://www.invisionpower.com)