Oil advice 90 Mazda truck..

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Jan 3, 2004
Nacogdoches, TX
Hello all, new to the forum here. Well, I have a 1990 Mazda pickup with the 2.6 liter fuel injected 4 cylinder and 164K miles. I have had it for the past 80K miles and it has always had dyno oil in it. The truck is supposed to use 10W30. About 2 years ago I began using Valvoline High mileage oil in 10W40 from advice of a mechanic because at the time it was using a quart every 3K miles. These engines are know for losing oil past the valve guide seals. I did that for a year and then just went back to using 10W30 in Castrol GTX. I never noticed a decrease in oil consumption and at this point it is using a quart at about 2600 miles. It does not seem to smoke any when consuming this oil. I still consider this acceptable but it is increasing some over the past couple of years. The truck gets used mostly on 25 mile commutes back and forth to work which is mostly highway and it is used only in eastern Texas. I am a big fan of synthetics but never switched due to the typical stories out there about switching over in a high mileage vehicle. I would like to know of what advice you have in which type/grade/brand of oil to use and if I should do the Auto RX. Also, I would like to switch to synthetic if it is possible. Thank you in advance. [ January 05, 2004, 12:35 AM: Message edited by: Robert M. ]
Hmmmm, maybe a thicker oil such as 10w40 or 15w40 would reduce consumption. In the worst case 20w50 should do it (but try the others first) and probably would work in your coldest cold start down in Texas.
The AutoRX will clean out your engine and will probably reduce consumption past the valve seals. AutoRX is a seal conditioner too, so it will probably rejuvinate the valve seals. And combined with cleaning the ring packs, you should see a bit more power as well as less consumption. If you already have 164K on dino, my advice is to run the AutoRX and keep it on dino. The rumors of changing to syn on a vehicle are said to be untrue, but my friend gave me a perfectly good '89 Chevy 1/2 ton that had a bad cylinder apparently due to running syn on a high mileage dino fed truck. The rings in the #1 cylinder were broken up with only 101K on the original engine. My theory on this is that the Mobil 1 was cleaning the engine, and it must have flushed some abrasive sludge into or out of the ring pack, breaking it up in the process. So if you want to go synthetic I highly recomend using the AutoRX first (use the over 100K application) before switching.
I personally, would be cautious using an engine cleaner on a high mileage vehicle. I messed up big time once, using a can of motor flush on an old pickup I bought. It was using a little oil when I bought it, and I could tell the engine was pretty dirty, so I put a can of motor flush in it at the next oil change, and it REALLY started using oil after that. Apparently, the sludge was helping seal everything in the old worn out engine. I had used it before on other vehicles with good results, but because of that experience, I'll never use it again. Of course the Auto RX is far superior to Gunk Engine Flush, but it would seem to me that the end result would be the same. One thing that might help you though is this. I had an old tractor once that the rings were worn out, and it used a lot of oil. And after trying all kinds of oil thickeners(ie STP, Smoke Stop, etc), I took the advice of a guy at NAPA, and tryed Morey's Oil Stabilizer, and it worked great. It still used a little oil, but not like it did. I don't know if it's still around or not. After I sold the old tractor, I never really had any need to buy any more of it. NAPA used to carry it, and I've seen it at some truck stops. I've seen a product since then called Lucas Oil Stabilizer, and it looks similar. The guy at NAPA said that the Longview Police Dept used Morey's Oil Stabilizer on some of their vehicles. That's been several years ago, so I don't know if they are still using it or not. But I would try a thicker oil or oil additive before I would try cleaning the engine. IMHO [Smile]
I would suggest using an API SL/CI-4 15W-40 "diesel" oil. Any oil that is rated CI-4 will have a high TBN and should slowly clean your engine. It may be a good idea to change your oil filter and top-up your oil at about 1,000 miles and change your oil and filter at about 3,000 miles. I also suggest using AutoRx. AutoRx should clean your motor slowly and not release a lot of crud at one time. I would estimate that going to a 15W-40 oil (from 10W-30) will cut your oil consumption by about 50%. If you decide to use AutoRx then you should be able to use an synthetic oil safely after you have completed the AutoRx cleaning and rinse cycle. The API SL/CI-4 15W-40 motor oils have a very robust additive package and should be able to go at least 5,000 miles or six months in a mechanicaly sound and fairly clean motor. With a lot of highway driving it may be possible to go as long as 7,500 miles or even longer between oil changes.
Like Sin city said. I would use a 15W-40 diesel oil like Delvac 1300 or Chevron Delo. There are about $6.00 a gallon.
I think 1 quart in 2600 miles is acceptable in this engine . I also think a 15/40 HDEO is just to heavy a VI at 40c for year round use in a OHC engine of this type . Overtime both engine wear when the ambient is very cold and the fuel mileage loss would be noticeable I dare say [Smile] Thats why the makers came up with these HM oils . For this engine I think the Pennzoil HM or Castrol HM oils would be the ticket given the wear protection and really good TBN retention I've seen in the used oil analysis's here vs switching to a synlube at this stage in the engines life . You should be able to go 5k intervals easily and get better fuel mileage than if you used a 15/40 engine oil . Now if you could find a 10/30 low sulphated ash diesel oil that might be a different deal .
I'd run the Rotella T, 5w-40 in this engine year round or the similar Delo 400, 5w-40. Both are very good, GP III based petroleum oils ...The 5w-40, Valvoline synpower is also very good and you can find that at some NAPA stores. Tooslick [ February 15, 2004, 08:05 AM: Message edited by: rugerman1 ]
Thanks for the many replies. Well, now I have a bit of confusion and more questions. I think the biggest agreement seems to be to stick to dyno oil which is fine with me. The Auto RX is very appealing to me so I would like more opinions of using it in my truck. I guess I am still confused on which grade of oil to use. I feel that my oil consumption is truly not too bad (especially at this age and mileage) so it seems like I shouldn't go too much thicker than the recommended 10W30. I would like more info/opinions on 5W40 and HighMile 10W30. I had previously used Valvoline HighMile 10W40 for about 24K miles then went back to regular Castrol GTX 10W30 as I didn't see a noteable decrease in oil consumption. Thanks again and I have spent many hours on this site so far.
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