I have about 100k on my 92 Cummins. I have just started towing an 11000lb fifth wheel. Since I have 354's and tall tires she works pretty hard at times. I was wondering if I put in a couple of quarts of synthetic motor oil with each change if it would protect the engine better? Is mixing petroleum oil and synthetic a bad idea? If it's they way to go will it improve milage?<br><br>Thanks for the help<br><br>Gary

 

Well the synthetic vs dino oil is a hot topic at the best of times.<br>I can tell you that pretty well all true full synthetics can be mixed with regular oil without any major problems.<br>There are some who say the synth. is a waste of money, others feel it was responsible for new oil leaks developing, and others, like me who have not had a lick of trouble since I changed over.<br>I do not subscribe to the high end extended drain intervals. I do go a bit longer with the synth. than I would with normal oil though.<br><br>I use amsoil, 15W-40 HDD (heavy duty diesel marine)<br>No problems so far.<br><br>bob.

 

Gary, I am a believer in synthetic lubes. Most synthetics are compatible with petroleum oils. Synthetic lubes are highly detergent, and can tend to clean out some sludge, and enable some leaking. This is most evident in gassers, however. You would need to be aware of the possibility that any current leaks could be increased.<br>A couple of quarts won't do you much good, as I would hope that you are using a high quality oil anyway, and changing @ proper intervals, using quality filters. <br>A full synthetic change-over, and maintenance program will cost you more, but may give back a little in economy. Moreover, you will know that you are doing your best to protect your investment.

 

Most synthetics are compatible with petroleum based motor oil, however, I'd run one or the other and not mix 'em. 80% of motor oil is basestock, the rest is additives. Both dino and synthetic use the same additives, it's the synthetic's basestock that will hold up much longer, and provide protection at temperature extemes.<br><br>All synthetic oils are not the same. Alot of the stuff on the market today are called Group III oil, which is hydrocracked petroleum base stock oil. It's refined purer. Better than regular dino basestock(Group I, Group II), but end consumer pricing is up there with the Group IV and Group V synthetic oils. <br><br>Extended oil drain intervals are one plus with full synthetic. Given the rather large sump capacity of the Cummins, I feel comfortable doing that. Even the guys on the oil forum comment on how clean the 5.9L Cummins runs based on oil analysis reports of used oil.

 

While I am a synthetic oil dealer (check my sig below) and a firm believer in the use of synthetics, if you have 100,000 miles on your engine with no problems using dino oil (as it is called), I would be inclined to stay with what I had if I were in your position. As long as you are using a good quality diesel engine rated oil, working that engine is the best thing you can do for it and the oil will protect it if you change it at regular intervals. I would not however recommend mixing the two oils together. While it would not harm the engine, it would be a waste of money in my opinion. You should stick with one or the other. The side covers were leaking on my old 89 at 85000 when I went to synthetic in the engine. I heard all about the &quot;will cause leaks&quot; stuff and decided to use it anyway. About a month after running the synthetic, the leak stopped and never leaked again to the day I traded it with over 142000 miles on it.<br>There is all kinds of documentation out there on the use of either oil and it will start a war if you ask which is best. The main thing is do the research, ask around, get the facts, and then run what you feel comfortable with since it is your truck. Some people change the oil every 3000 miles, some go 5000, and others more. The quality of oils today I believe is far superior to what we had years ago and your truck will probably go 300000 miles or more on the oil you're using now.<br>This probably didn't answer your question bit I will say go one way or the other and don't mix and you'll be fine.<br>Hope this helps.

 

Thanks Guy's<br><br>I am using Penzoil 15-40 diesel long life in her. I have been using the same oil since I bought her new. Doesn't burn any and seems to be fine. Never had a lick of problems with er. I change the oil and filter every 4k using either the Dodge filter or Frams. I also grease er every 2k. <br><br>I just want to do the best I can for er. I realize the 354's with the 33&quot; tires arent the best combo for towing but at the time I wasn't doing much towing and it was fine. <br><br>It sounds like I should stay with what I have. I guess if it ain't broke don't fix it huh?<br><br>Thanks again<br><br>Gary

 

Shell Rotella is another good diesel oil but it smells for about 1000 miles or so after a change. At 4000 mile oil changes, you are doing very well. I use to go an even 5000 when I was running Rotella and could have gone 10000 with no problems I believe. I would recommend you stay away from the Fram oil filters and go with Dodge, Cummins, or Fleetgaurd. There is history of the Fram coming apart and clogging up the pee pipes or piston cooling pipes in the engine.

That is low mileage for a truck the year of yours. Mine is a 99 and I'm coming up on 120000 already. I pull up to 26000 pounds with mine.

I would be more concerned about the rear axle lube and the trans lube in yours than the crankcase. You may want to look around and get the facts and change those if you are pulling that much weight.

 

I heard that. I am running synthetic in the five speed trans but dino in the rears. Couldn't come up with the right synthetic for the rears. If anyone knows what goes in there please let me know. I think I would rather use synthetic. If anyone thinks differently let me know.<br><br>Thanks again

 

I'm running AMSOIL Series 2000 75 W 90.

 

Me too on the Series 2000 75-90. I just don't think that I tow heavy enough to justify the 140. I used the regular Amsoil 75-90 in my Gen 1. Pre series 2k at the time. Same in the Getrash, and NP205. Still going w/ no wet parts work since the updated Getrag @ 5500 miles. I don't know current mileage, but it was @ 250+K when sold nearly two years ago. I know the owner, and know that the maintenance has not been performed like I did it .

 

Synthetic lube in the axles is a good idea. I do run Amsoil in mine, but there are other synthetics out there that are just as good and may be more cost effective for you. With Amsoil, you'll either have to find a dealer and pay full retail, or log on to their website, pay a fee for preferred customer, and buy at &quot;dealer cost&quot; and have the product shipped to you. Oil is heavy, and shipping can be expensive. <br><br>Other synthetic gear lubes to choose from are Mobil 1, Red Line, and Royal Purple. Mobil 1 is readily available over-the-counter, Red line is available online and offers free shipping on orders over $39, and Royal Purple has a website giving where to purchase information. <br><br>75W-90 is common weight, xxW-140 wouldn't be a bad idea if you do heavy towing. Regards

 

Availibility of synthetics is an issue some times. You can look around for the ones RM mentioned above and buy what best fits your wallet and makes you feel best. I try not to mention any names to avoid wars and flames unless someone asks.<br>Sledpuller in in the western part of Pa somewhere and can get you the AMSOIL stuff if you decide to go with it. If you use enough of the product, it is worth setting up a preferred customer account and you pay dealer prices but you still pay shipping so any savings are usually cancelled out. I just PM'd someone with the instructions on how to do that if you like, I can dig them up and send to you.<br>Send me a pm with what you are looking for and I will give you preferred customer prices to compare with what you can get at your local parts store if you are interested. Won't cost you anything to do that.