Using synthetic oil and I change all 3 at 5K since it's so easy to do when it's already on the lift!!

 

my Road King has 30k on it, and I change Eng, Trans, and Pri every 2500 -3000 (chg all 3bikes at the same way). They all come out looking almost as clean as the day I changed them (I suck at keeping up with changes on my truck though)
HD syn in the engine
RedLine in the Trans
HD Trans oil in the primary

 

all three at 5k intervals - engine oil every 2500, just me....synthetics all

 

Regarding some of the differences between dino and synthetic oil. I have a brother-in-law who works for a small oil company that does a lot of testing of oils for many other companies. I asked him about the dino vs synthetic oil controversy. He said that synthetic oil will last longer with fewer impurities than dino oil. You can change your oil less often with syn oil over dino. But, if you change your dino oils on a regular basis you will be just fine. The parafin-based oils will need to be replaced more often than others. In an older engine that has always used dino oils if you switch to synthetic you may well see leakage because the syn oil is more slippery and will find its way in the crevices of the crap left over from the gunk of the dino oil. Otherwise, no harm. He said he wouldn't change because of that. The most important thing with the dino oils is to change them on a regular basis so you can keep the impurities from damaging the engine parts. The oil is relatively cheap enough that it is just good insurance.

 

I'm a simple man .....car, truck, scooters; 3K mile oil change. Scooters tranny and primary at 6K miles. Mobile or Purple synthetic oil.

 

I do intervalls as per the harley manual,engine at 5k,...primaryat 10k,..and trans at 20k.
engine gets syntheticMOTOR oil(its a motor) ,Primary and trans get synthetic GEAR oil(they are gears). pretty easy

 

06 Cop Glide

Change all three every 2500 - 3000 miles

Mobil 20/50, 75/90/Formula +

 

Engine - every 5K, Mobil V-Twin and previously Mobil 1 15-50W
Primary - every 10K, Mobile MX4T
Tranny - every 10K,Mobile 75-90W

100k miles in total on my currentbikes with these oils and no problems

 

Thank for the quick replys. My practice was to change the primary and tranny fluid at every other oil change. Now that I am using synthetics like most here, I'll continue the practice, but extend the intervals. Right now I have Syn 3 in the engine and primary and Belray in the tranny. I'm switching to Amsoil for the engine at the next change. Thanks again.