# For members with oil Temp gauge in their car....

#### 427Z06

quote:
Originally posted by zoomzoom: I guess if the car run cool enough then 20wt would behave like 30wt?
The 20 Vis oil would have to run at least 15F cooler for that to be the case. Although, it's an interesting thought.

#### cryptokid

if a synthetic oil was truely better at heat exchanging then it would have higher oil tempatures. a syn is suppose to pull heat off the engine's parts. well this heat has to go somwhere! eventually this heat gets out through the surface of the engine and or a heat exchanger. but the heat has to get from the engine to the air. it travels its path via the oil.

#### Quattro Pete

I've ran 0w-30, 5w-30, and 0w-40 oils in my car, and when I drive steadily @ 75mph I do not see any oil temp difference between these oils. The temp stays at around 190F. However, when I drive hard, I can see the oil temp rise quicker with a 30-weight than with a 40-weight. I guess it has to do with the fact that the thicker oil takes longer to heat up. And when I say rise, I'm talking an increase from 190F to about 210F, so nothing major that I'd be concerned with. Cheers,

#### kevm14

quote:
Originally posted by cryptokid: if a synthetic oil was truely better at heat exchanging then it would have higher oil tempatures. a syn is suppose to pull heat off the engine's parts. well this heat has to go somwhere! eventually this heat gets out through the surface of the engine and or a heat exchanger. but the heat has to get from the engine to the air. it travels its path via the oil.
Measuring the oil temp at only one point would tell you nothing then. You'd need at least two points of measurement. For what you're talking about, the ability of the oil to be a heatsink, you'd want a sensor right at the post-oil cooler pre-engine point and one right as the oil leaves the engine. The difference between these two numbers is how effective the oil is at picking up heat.

#### zoomzoom

would thiner oil(20wt) remove heat from engine better/faster then thicker oil(40wt)?

#### mountravlr

Probably not measurable to any reliable degree. I''ve attached a ScanTool to the OBD II connector, and the operating temp varies from 187-193 with 0W-30, whether it's highway or city, or idling. The thermostat and the radiator fan provide enough variation to render oil temp efficiency relitively meaningless, IMO.

#### zoomzoom

mountravlr Now if you could get the same range using the 3 conditions I mentioned in my first post with 0W-20, 0W-30 and 0W-40 then we could see if there is any difference.

#### 427Z06

quote:
Originally posted by mountravlr: The thermostat and the radiator fan provide enough variation to render oil temp efficiency relitively meaningless, IMO.
Wow, your the first person I ran across that actually measured their oil temperatures and found them so consistent. Maybe the value your reading is the dummied down value sent to the "idiot gauge". FYI, the "idiot gauges" they put on most cars today, barely move out of the normal zone unless the actual temperature is way above the nominal zone.

#### kickster

Both my VW have vdo temp gauge. For some reason my Race car with lots of mods is running cooler with AMSOIL 10w40 or 20W50 than my stock Golf running AMSOIL 5W40!!

#### zoomzoom

It has been said on this board that using lighter oil like M1 0W-20 will make engine run cooler. Has anyone been able to verify this by actually noting the difference in their oil temperature between 30/40wt and 20wt given the same conditions? For example what was the oil temperature in: 1. Regular city driving 2. Highway driving 3. High-speed highway driving(like 80 mph+) In another word if you get on highway and drive for 10min at 75mph would temperature be lower and by how much if you used XX-20 versus XX-30 or XX-40? I guess if the car run cool enough then 20wt would behave like 30wt? I whish I had oil temp gauge on my car Thanks for your answers, ZoomZoom

#### zoomzoom

Do you have oil cooler or bigger radiator on your race car...or maybe lower temp thermostat?

#### Ryan00TJ

Well on Chevron Supreme 10W-40 my 2.5L Wrangler TJ would run about 220-225 degrees at 70mph on the interstate. After switching to Schaeffer's 15W-40 PAO Blend the normal now is 210-215 at same speed and under the same conditions. I've also noticed the 15W-40 keeps better hot idle oil pressure than the 10W-40 by far.

#### dagmando

I had a 1996 VW Passat GLX VR6 that had an oil temp gauge and 10w-40/20w-50 oil was consistantly 10-15 degrees hotter then the 10w-30. 10w-30 idle was always about 202* 10w-40 212*, highway 275moh 10w-30 was 216-220 10w-40 was usually 228-234. It as definetly noticable when I swithed from the 10w-40 I had in there to the 10w-30 the dealer was putting in for their \$20 oil change. I always looked at the oil temp gauge during the summer. I had it once up to 248* driving 80-85mph for 3-4 hours while 90*+ and HUMID. This was with the Sypower 5w-40. [ July 23, 2004, 02:56 PM: Message edited by: dagmando ]

#### kickster

no I dont have oil cooler in either cars. I have lower fan switch and thermostat on the race car but it has a smaller rad compare to the golf.

#### FowVay

dagmando, I experience the exact same thing in my 1997 Passat. I normally use 15W-40 when weather permits and it always runs hotter than a 10W-30 does. I don't know how accurate the MFA indicator is on these cars but I can repeatedly show these variances.

#### 69 Riv GS

Interesting topic!
quote:
I had a 1996 VW Passat GLX VR6 that had an oil temp gauge and 10w-40/20w-50 oil was consistantly 10-15 degrees hotter then the 10w-30. 10w-30 idle was always about 202* 10w-40 212*, highway 275moh 10w-30 was 216-220 10w-40 was usually 228-234.
It seems plausible that the slower circulating 40/50 weight would have more time to absorb component heat, therefore raising its temp. Think about the cylinder walls(high temp area); a thick oil will spend more time there before it drips/is pushed off. [ July 24, 2004, 10:20 AM: Message edited by: 69 Riv GS ]

#### palmerwmd

dagster: Did you check your manual? When I had my 94 passat VR6 the thinnest oil authorized ( even in winter) was 15w-40 and the summer oil wa 20w-50. I understand the new recomendation is 5w-40, but thats more a result of modern oils being better and being produced with wider spreads. VW engines are hard on oils and back in that day VW adamantly warned against use of 30 weights, only 40 and 50 were recomended. Fred..

#### 69 Riv GS

quote:
Originally post by me: It seems plausible that the slower circulating 40/50 weight would have more time to absorb component heat, therefore raising its temp. Think about the cylinder walls(high temp area); a thick oil will spend more time there before it drips/is pushed off.
I take that back. A lower viscosity fluid more efficiently transfers and dissipates heat. It's explained here.

#### zoomzoom

So 40wt will run hotter oil temp then 30wt, given this can we say that both oils will be at about same viscosity under higway driving conditions? Or in another words 40 wt will behave like 30wt since it is running hotter, if so what is the benefit of running 40wt in first place?

#### XS650

quote:
Originally posted by zoomzoom: So 40wt will run hotter oil temp then 30wt, given this can we say that both oils will be at about same viscosity under higway driving conditions? Or in another words 40 wt will behave like 30wt since it is running hotter, if so what is the benefit of running 40wt in first place?
All else being equal, 40 will only run a bit hotter than 30 wt. Not nearly enough hotter to make it the same viscosity as 30 weight. I switched my car from 5W-30 synthetic to 15W-40 HDEO. There isn't enough temperature difference to say for sure if it runs hotter, cooler or the same using a digital oil temperature gauge. You need some well controlled tests or need to really be a believer to see the difference in the real world.