Mixing oils...
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Lead Driver
Joined: Mar 2008
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From: Near Los Angeles
Mixing oils...
I have been using Pennzoil synthetic blend for the last couple of oil changes, a 5/30 weight. Yesterday I tried a full synthetic, and added a qt. of normal 5/30 oil. Also, I always add the zinc additive to the mix. With the full syn. the psi went alarmingly high, 60 psi just cruising with my foot barely on the gas, rpm low. That startled me. I parked it and began researching. I decided to go with one brand, all the same viscosity, with the zinc. I learned that the additives vary from brand to brand, and that it's not healthy to mix them.
My lesson learned was that tried and true beats the cheapo stuff, and that the cheapo stuff usually ends up costing you/me more in the long run. Expensive oil change.
My lesson learned was that tried and true beats the cheapo stuff, and that the cheapo stuff usually ends up costing you/me more in the long run. Expensive oil change.
Hotshot
Joined: Feb 2004
Posts: 10,842
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From: The Shenandoah Valley
I've run 20w50, 15w40, 10w40 .... and at times have used some 10w30 in my '77, I don't mind a mix. I use synthetic in some vehicles, synthetic blends in others, but have never put any in the '77. When I use up my 15w40, I have a case of Kendall 20w50 I'll use in the '77. It's a few years old, so it'll get a really good shake to get all the extra goodies mixed back in like pour a third in, then close & vigorously shake the bottle or jug, then pour the remainder in.
Last edited by tbear853; Yesterday at 10:15 AM.
Lead Driver
Joined: Oct 2018
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I only run 10/30 or 10/40 in my classics. 15/40 would be okay in hot climates. the lightweight oils were not made for old rigs, I'm not sure they're good for new ones. it's all about fuel economy not what's best for the engine.
Lead Driver
Joined: Nov 2000
Posts: 6,637
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From: Albuquerque
Mixing syn and reg oil is not a problem. There are premixes on the market that are a combo. You wont get the full benefit of syn. Also syn is slicker than reg oil and should not cause a high pressure. Possibly you used too much zinc and it clogged the filter? Also I run a much thicker oil in my cast iron 400 hot rod. especially in the summer.
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Lead Driver
Joined: Mar 2008
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From: Near Los Angeles
With the Pennz 5/30 I can tell how hot the engine is by the psi of the oil pressure gauge. On first start in the morning I'm reading 50 psi at idle. As the engine warms the psi drops until fully warm when it reaches 28 psi at idle.
With the full synthetic 5/30 and a qt of traditional 5/30, on first start I have 60 psi at idle. That disturbs me. It seems like a lot of resistance/back pressure. I can't help but wonder if all the v. train and bearings are being properly lubricated.
I am surprised that 2 oils, one traditional and one syn, both the same viscosity, will behave differently.
I believe I will try to find the tried and true Pennzoil blend. I would like to try to thin the oil I now have, since an oil change these days costs over $60, but that is a fair price for peace of mind.
With the full synthetic 5/30 and a qt of traditional 5/30, on first start I have 60 psi at idle. That disturbs me. It seems like a lot of resistance/back pressure. I can't help but wonder if all the v. train and bearings are being properly lubricated.
I am surprised that 2 oils, one traditional and one syn, both the same viscosity, will behave differently.
I believe I will try to find the tried and true Pennzoil blend. I would like to try to thin the oil I now have, since an oil change these days costs over $60, but that is a fair price for peace of mind.
Fleet Mechanic
Joined: Sep 2014
Posts: 1,627
Likes: 79
From: NE Texas
according to a pretty knowledgeable fella on another forum I frequent, as little as one quart of full synthetic oil mixed with several quarts of dino oil gives you essentially all the benefits of the synthetic. I normally run Mobil-1 10W40, as their data claims a ZDDP of 1200, and when I wanted to clean the old girl out I used Rotella 6 for one change. No new leaks, really dirty oil when I changed it. A while back AutoZone was disposing of their Castrol Classic GT1 20W50 for like $2 a quart and I bought a dozen for another car.
Cargo Master
Joined: Oct 2020
Posts: 2,695
Likes: 791
It is very important to not go overboard on ZDDP. The amounts used in the oil depend on the additive package of that given oil but too much is probably worse than too little. Too much will cause corrosive wear and this can happen surprisingly fast.
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