So basically....I have my oil level on my dipstick reading to the lowest line (which says add 1 quart). I currently have "standard" Harley oil in my engine, bought from the dealer. I found an extra bottle of fully synthetic Castrol 10w-60 that I used for my BMW M3 before. Can I use this and add half a quart?

Thank you in advance oh great forum

 

Keep your oil level close to the lower mark. Running oil level higher can lead to some oil blow-by into the aircleaner through the breather vents. 20/50 is recommended, folks use 15/50 Mobil 1 as well.

John

 

HECK NO!

Not unless the 'standard' Harley oil is their fully Synth Oil as opposed to their Petroleum type.

Never mix Petroleum and Synthetic oils if at all possible.

 

You'll be fine mixing the two. The fear with mixing conventional and synthetic oils is that the two will coagulate into some sort of gel - I've never heard of that actually happening. I don't believe there's any science to back up that fear. They should be compatible.

That said, I wouldn't mix oils routinely. Top off the tank with whatever you've got, then drain it and put in whatever your preferred oil is when you get the chance.

 

Most of these bikes seem to want to run about a half a quart low. Any more will cause blow-by and put oil into your throttle body. Oil brand loyalty is like a form of religion to some. Anything that deviates from their chosen brand is sacrilegious. Some will swear by 'dino' oil while others say you MUST use synthetic. A very wise old engine builder once told me that ANY oil was better than NO oil. So in a pinch use what ever oil you can get (dino oil and synth will blend fine without issue and is even sold that way) but frankly the best oil is one designed for the intended purpose. SO...for me that would be an oil designed for four stroke engines that use a separate oil for the engine and clutch. I prefer synthetic for it's ability to continue to lubricate at much higher engine temps than petroleum based oil. There are any number of excellent choices Mobil1, Red line, Harley's syn3 (which is a synth-dino oil mix I believe), royal purple, etc. I am currently using 10-50 Liqiu-moly 4T. I have about 2,500 mi. on it (bike has 23,000 mi.) previously I used Mobil 1 since I built this motor 18,000mi.ago. My motor is an 02 TC 95" with ported heads shaved .020 w/oversize valves, Andrews 37 cams' Supertrap exh. and a power commander. Buy the best oil you can afford but stay close to what an Engine builder would recommend. IMHO

 

Thanks for the replies fellow riders I went with a tad of Mobil 1 Synthetic 20w-50 V-twin oil and added juuuust enough to get the dipstick to measure a tad above halfway.

 

My understanding of petrol car oils vs motorbike oils is car oils have friction modifiers in them and bike oils dont. In short this means car oils can make your clutch slip. I guess in a Harley its a different set up though. But some people do talk about "using the same oil in both holes"?

https://www.google.co.uk/webhp?sourc...0clutch%20slip

 

When I have switched back and forth between synth and standard oil on my Sportsters, I never drained or flushed the system. So got a mix when I made the changes (over the years, I have had no issues).

Personally, if I was low on my oil and all I had was synth at the time, I would pour in the synth and not lose sleep. I had Harley Synth-3 in my 2007 and was going out for a ride, noticed I needed about a 1/4 of a quart and all I had was Mobil-1 20-50W (non-synth), poured it in. Bike was okay until next oil change. Sometimes people get too **** when it comes to oil and motorcycles.

Now...if we were talking primary/transmission oil, I would be careful about the type of oil I put in due to the clutch and yellow medals (but with your engine oil, no issue).

 

API says that all oils have to be compatible and can be mixed. What do you think simi syn is made from?

 

You're wrong about that. Synthetic and non synthetic oil mix just fine without any problem.

OP do not take the above quoted post as factual.