Why does oil weight matter in hotter ambient temperatures?
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Thread: Why does oil weight matter in hotter ambient temperatures?

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    Opeler sgtfroggy's Avatar
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    Why does oil weight matter in hotter ambient temperatures?

    This question is more about my daily driver (RAV4) but also applies to my Opel.

    I just moved to Arizona and it turns out it's super hot here. My RAV4 manual says that 5W-30 is preferred for under 100 degrees, and that 10W-30 is recommended for 0 degrees through over 100 degrees. Since it's now consistently over 100 degrees, I am deciding if I need to switch to 10W-30. I understand why the weight matters at cold temperatures, but not at hot temperatures. Since the thermostat keeps the engine temp at 170 degrees, the engine doesn't get any hotter here than it did in Seattle, just gets there faster. I would assume that if 5W-30 is fine for 170, there is no benefit to 10W-30. Can anyone explain what I am missing? Or is it just a matter of time until I find my cooling system can't keep up with the engine?
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    3000 Post Club m610's Avatar
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    Perhaps the viscosity when you first start the car?

    Total guess.

    Mike
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    Opel Rallier since 1977
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    The thermostat only set the MINIMUM temperature.... it does not set the maximum temperature. The maximum is set by the cooling system capacity and the ambient temps. Unless your cooling system is unusually capable, then your engine oil IS going to run hotter in AZ.
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    I don't know why they would *prefer* 5W30 over 10W30 for ambient temperatures under 100. Is that the wording they used in the manual? I can see them approving 10W30 in addition to 5W30 for hotter ambient temperatures but the 5 vs 10 makes no difference when the engine is warmed up in hot weather.

    What would matter is how 5W30 flows vs. 10W30 at initial start temperatures. If it's 75 degrees in the morning they would both perform about the same but, really, you'd need to know the exact flow vs temperature curves of each oil across the range of operating temperatures to select the "best".

    I'd think 5W30 in a modern car should work just fine in Phoenix. When I lived there with my GT I used 10W50 or 15W50, because the engine ran so hot AND internal tolerances weren't as tight as on modern cars, but if 5W50 was available at the time I would have used that.
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    The ambient temp in Arizona is hot, but here in the South, we get the heat and the Humidity. If not hijacking this thread, but what about reguler driving on the weekends? MICAH1 and I were talking about viscosity during the summer. This is part of my reply. I always used Vavoline 20W-50 in the summer and 10-30 Vavoline winter. Tom, (The Cub) did a real nice rebuild, 247 pages worth, on a 1.9 to 2 litre. Good read. The oil that he is using has Zinc in it.. Read this.https://www.restore-an-old-car.com/b...ssic-cars.html He might be on to something. Not cheap by any means, but maybe so since we're running "Classic cars" I think you can add Zinc seperatly, so you could run the oil you want, add this and keep on going. I ran the engine on synthetic for the first 1000 miles. All the seals had been replaced though. Then started Vavoline 20w 50 and had good oil pressure during the summer. 10-30 winter. What are others running summer/winter? I also added this to my next oil change, courtsey P. J Ramono, https://vod.ebay.com/vod/FetchOrderD...&ul_noapp=true Thanks, Jarrell
    Last edited by soybean; 4 Days Ago at 09:48 PM. Reason: spelling
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    Manta Rallier is spot on. A thermostat is there to set the minimum temperature for the water. And an electric fan is there to control the maximum. Whether or not the fan actually maintains the temperature below the maximum is up to the thermal and load conditions of the day.

    If your car doesn't have any direct cooling for the oil, all of its cooling will be coming from heat transfer through the block to the water or out the pan. On a cold day the pan can do significant work to cool the oil. That effect goes away on a hot day.
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    If you don’t see temperatures below 0 in the winter, you can run 10w30 year around. BTW, never add anything to your oil. Modern oils have everything they need to protect your engine.
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    Thanks for the responses, that makes sense that it would get hotter overall. So far based on the gauge it seems to be holding the same max temperature, but I don't know how accurate the gauge actually is.

    For reference, here is what the RAV4 manual states.
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    According to that chart 10W30 is acceptable as long as the temperature is 0 or above. I assume that it doesn’t get below 0 where you live?
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    Quote Originally Posted by sgtfroggy View Post
    So far based on the gauge it seems to be holding the same max temperature, but I don't know how accurate the gauge actually is.
    The gauge is probably pretty good for water temperature but it will be off on oil temperature.

    If you have an OBDII scan tool, you can usually stream the temperature information for non displayed sensors like oil temp.

    Plug it in and take a drive during the day when it's really hot and note the max temp of the oil and water. Wait a few hours and take the same drive at night when it is a lot colder. Take note of the oil and water temperatures again. Ideally there is no change in the delta, but the amount of delta is telling information for how temperature dependant your oiling system is.
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    Quote Originally Posted by Dmcbrass View Post
    ... BTW, never add anything to your oil. Modern oils have everything they need to protect your engine.
    Umm, maybe true for modern engines and modern oil, but just about all the experts and many of the non-experts () suggest that flat tappet engines such as our Opels require oil with ZDDP, so either buy oil with it (most do not have it these days), or add some to it, or be prepared to replace your cam and lifters in the near future
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    Quote Originally Posted by kwilford View Post
    Umm, maybe true for modern engines and modern oil, but just about all the experts and many of the non-experts () suggest that flat tappet engines such as our Opels require oil with ZDDP, so either buy oil with it (most do not have it these days), or add some to it, or be prepared to replace your cam and lifters in the near future
    How much additive do add/gal and of what brand? Thanks Jarrell
    Last edited by soybean; 3 Days Ago at 11:43 PM.
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    I've been spending a lot of time in Mopar-land for some years and of course, ZDDP is a big topic there due to all the high performance engine builds. Some things to know:
    - Older typical levels of ZDDP in the age of most of our Opel engines was in the 1200-1300 PPM range. Those levels continued in oils for several decades.
    - The levels started dropping about 2004-2005, required by the EPA to have less phosphorous (the 'P' in ZDDP) and thus less effect on the sensors in the emissions systems.
    - Currently, the SN grade oils are running typically in the 800 PPM range for ZDDP.
    - The need for higher ZDDP levels is heavily dependent on the contact pressures between the lifters and cam lobes. This contact pressure is driven by the valve springs, and by the ramp rates on the cam lobes plus valve train parts weights. The former creates a static level of pressure and the latter 2 contribute to dynamic pressures that vary with RPM's.
    - Lighter stock springs and less aggressive cams and lower RPM's of often allow the newer lower levels of ZDDP to be run A-OK. I have not been running any Opels since the ZDDP levels dropped to be able to intelligently say what will work OK with the stock Opel 1.9L parts for example, but stock mopar valvetrains (like 225 SLANT 6'S, AND 318's and 360'S) seems to do fine with the lower ZDDP levels. (Their typical closed valves springs pressures are in the 80-90 lb range for reference.) Opels have very light valvetrains by comparison, so the stock systems 'ought' to give less contact pressures are moderate RPM's.
    - Excessive ZDDP is thought by some to cause its own problems; spalling of the surfaces is 1 issue I have read about. So it is not a case of "If some is good, more is better!"
    - It is considered best to get your oil with the desired ZDDP level in it already; ZDDP additives may contain components that can fight the oil's manufactured additive package. You can look up the ZDDP PPM specs on an oil spec sheet; if they do not list ZDDP specifically, look for the PPM level of 'zinc'.
    - If you want to use an additive, then I can tell you that 1/2 can of Rislone Oil Treatment will raise an 800-900 PPM ZDDP level (like in a new SN oil) up to the 1300-1500 PPM range when added to 5 quarts.

    Hope all of the above is worthwhile!
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    2000 Post Club soybean's Avatar
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    Quote Originally Posted by Manta Rallier View Post
    I've been spending a lot of time in Mopar-land for some years and of course, ZDDP is a big topic there due to all the high performance engine builds. Some things to know:
    - Older typical levels of ZDDP in the age of most of our Opel engines was in the 1200-1300 PPM range. Those levels continued in oils for several decades.
    - The levels started dropping about 2004-2005, required by the EPA to have less phosphorous (the 'P' in ZDDP) and thus less effect on the sensors in the emissions systems.
    - Currently, the SN grade oils are running typically in the 800 PPM range for ZDDP.
    - The need for higher ZDDP levels is heavily dependent on the contact pressures between the lifters and cam lobes. This contact pressure is driven by the valve springs, and by the ramp rates on the cam lobes plus valve train parts weights. The former creates a static level of pressure and the latter 2 contribute to dynamic pressures that vary with RPM's.
    - Lighter stock springs and less aggressive cams and lower RPM's of often allow the newer lower levels of ZDDP to be run A-OK. I have not been running any Opels since the ZDDP levels dropped to be able to intelligently say what will work OK with the stock Opel 1.9L parts for example, but stock mopar valvetrains (like 225 SLANT 6'S, AND 318's and 360'S) seems to do fine with the lower ZDDP levels. (Their typical closed valves springs pressures are in the 80-90 lb range for reference.) Opels have very light valvetrains by comparison, so the stock systems 'ought' to give less contact pressures are moderate RPM's.
    - Excessive ZDDP is thought by some to cause its own problems; spalling of the surfaces is 1 issue I have read about. So it is not a case of "If some is good, more is better!"
    - It is considered best to get your oil with the desired ZDDP level in it already; ZDDP additives may contain components that can fight the oil's manufactured additive package. You can look up the ZDDP PPM specs on an oil spec sheet; if they do not list ZDDP specifically, look for the PPM level of 'zinc'.
    - If you want to use an additive, then I can tell you that 1/2 can of Rislone Oil Treatment will raise an 800-900 PPM ZDDP level (like in a new SN oil) up to the 1300-1500 PPM range when added to 5 quarts.

    Hope all of the above is worthwhile!
    Thank you, Jarrell
    You lose your dreams, you lose your mind. (The Rolling Stones)

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