1999 3.8 Mustang Oil Shopping

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Nov 17, 2010
I'll start off with I'm new here. I thought I'd start a post about my two vehicles; an 06 Grand Cherokee (WK) 4.7 and a 99 Mustang 3.8. I am thinking about switching oils in my car after searching through this site. I had the Mustang from new. I ran Pennzoil Yellow 5w30 exclusively for the first 65K, oil changes every 3K. I took the car in for the first time to the dealer at 65K for some work (A/C, plugs, wires, etc.) and decided I'd let them change oil while it was there. I found out after the fact that they put Syntec in it. I wasn't happy because at that time people were telling me that once you go synthetic, you shouldn't go back. So I didn't. Despite learning that it doesn't really matter since then, I have run only 5w30 Syntec with the Fram double guard to the current milage of 150K, changing at 5K, 5 1/2 K tops. I discovered here that Ford has been suggesting 5w20 in the 3.8 for years now. I know there was an issue and the Vulcan V6 switched, but i never heard about the 3.8. Probably not a huge deal, my engine seems tight, but valve train sounds are getting louder on startups. I ride 45 minutes each way to work, mostly cruising in 4th (5 speed) at about 50 mph. I have been good on this car; I idle until it comes off high, and I don't stomp on it but I will squeeze the pedal into the carpet from time to time to wind it out a little. So for sure, at least on the next change here in PA over the winter, I will use 5w20. I'm just not sure on the brand of 5w20. So.... now i am reading about Syntec and i feel like perhaps it's not the best oil out there for the money I pay at WM. I always liked the old Yellow Pennzoil and I'm thinking about switching to the Platinum or maybe the Ultra. I will continue to change at 5K and don't mind the price of up to 30 for a change. Maybe I'll stay with Syntec or switch to something else? I am interested in any advice, preferably advice with some good evidence as to why a specific oil would be good for the ol' 3.8 with push rods. Similar to the Mustang, I have been running Syntec 5w30 in the WK's 4.7 since 35K, changing every 5K. It's now at 50K. I'm thinking about going to Platinum in this one too. I should also add that other than a few longer family trips on the weekend, this Jeep does a lot of 10 minute trips down town. Any thoughts here? --Stemmy--
I'm sure the platinum or Ultra is good oil, but what about Fords synthetic blend 5w20. Seems to produce favorable UOAs here and is pretty cheap.Now in the GF-5 5 quarts.
I have a 2000 Ford Mustang with the same engine as yours. I saw the same set of information where Ford had re-spec'ed a lot of cars from a 5w-30 to a 5w-20. I learned however that our motors were NOT spec'ed back to a 5w-20 weight. Overall, I have heard great things about Pennzoil synthetic and conventional oils, so you can't go wrong with them. I have personally used Quaker State Ultimate Durability Synthetic in my car for the last two oil changes and my car has ran great on it. I also recently did an oil analysis with the synthetic which has found that the oil is doing a great job protecting the engine as well. You really can't go wrong as long as you are following your car manual's advice. Take care. Here is my OIl Analysis: http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2078182#Post2078182
my daughters '99 mustang has the 3.8 also, the 3.8 HAS been back-speced as far as '96. i have been using motorcraft 5w-20 since i bought it at 90,000mi., currently at 128,000mi with zero issues the motorcraft, even with the recent price increase, is still a very good bargain at $14/5qts. i really don't think brand is nearly as important as grade in this or most applications
OceanRocket24, What do you mean that you learned it was not back spec'ed? The TSB shows the 3.8 Mustang under 5w20? Maybe I missed something, I'll take another look. I must admit that it's going to be tough for me to put that in when the oil fill cap reads 5w30. --Stemmy--
I wouldn't lose sleep over the 5w20 vs 5w30 issue. Most likely I would keep running 5w30 simply because that is what has worked for you so far and because I doubt you will see any advantage to switching. As far as brand, both the Syntec and Penn Plat are great oil, again, would not lose sleep over either. Go for whichever is on sale or, as mentioned above, try out the Motorcraft.
I'll go ahead and recommend the Motorcraft synthetic blend 5W-20 as well. It's probably nearly as good as the Syntec you've been using, but at a terrific price. A 5K OCI shouldn't tax this oil at all - Ford recommends this oil for 10K OCIs in some of its newer cars. If you're dead set on full synthetic, you can't go wrong with PP.
Originally Posted By: Stemmy
OceanRocket24, What do you mean that you learned it was not back spec'ed? The TSB shows the 3.8 Mustang under 5w20? Maybe I missed something, I'll take another look. I must admit that it's going to be tough for me to put that in when the oil fill cap reads 5w30. --Stemmy--
Sorry, I don't mean to stir around wrong opinions or out dated facts, especially because there are already a lot of opinions on this site. You are right Stemmy, this motor was back-spec'ed at least through as old as 99', which is the car in question. You are right!
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