Oil change without flush

Hey all!

Just got a new kart and previous owner was using motul 300v 0w16 oil. I want to use 4t instead and I know people on both sides of the fence on whether to flush or just change. I’ve switched from 4t to redline in the past and all was well (as far as I know), but this is a newer engine, so I’d rather not risk it. However, there seems to be quite an opinion on flushing the engine as well, with some people swearing it damages seals and whatnot.

Is there any other way you guys have gone about this without flushing with mineral spirits, gasoline, etc…? I know there’s a risk on both sides but bad luck seems to always find me in this sport!

I’d recommend some sort of flush for sure a lot of the karting specific oils don’t match well

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On my oil changes I’ll drain the oil out the front drain hole with the block propped up slightly in the back. A quarter inch or so is plenty. After it’s mostly drained I’ll spray some brake-clean (or carb cleaner) into the lower front fill hole. It helps to use the little spray tube that comes with the spray can. Angle the tube so it points at the back side of the case and go from side to side as you’re spraying. Watch the color of what comes out of the drain hole. At first it’ll have a lot of fine black residue in it but then should run clear. Let the cleaner evaporate for a few minutes, replace the drain plug, and put in fresh oil. The first time you do this after a rebuild will be very dirty. As the engine wears in, there will be less residue.

That sounds good! So that process would flush the motul oil enough for it to be safe to put the briggs 4t in?

Redline is pretty popular, I think its cause its cheap and can be purchased in bulk. But I have more trust in Amzoil products like (T4). If you flush, people I know swear by flushing with mineral spirits.

The Motul and the Amsoil 4T are not that different. It’s not like castor based vs. petroleum or some of the compressor oils run many years back. Flush it as clean as you can with the spray, put in your new oil and run it in a very light practice session. Lift early, stay away from peak revs and just get the engine warmed up. A couple of minutes at most. Then repeat the oil change and you should be good to go. Running the engine gets to all the places that are hard clean out with spray or rinse. The temp also lets thing flow out easier.

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The Briggs 4T oil instructions say that when switching to it, pour in New Briggs 4T oil, run the engine for two or three minutes and then change the oil.


Since it was brought up, I have a couple (ok, a bunch) of questions… I’ve heard/read horror stories of switching oils without flushing and from what I can gather its due to the oil’s base being either PAO or PAG? What exacly is PAO and PAG? (I know just enough about chemistry to generally avoid setting myself on fire, but I do speak science and am very curious).

It often seems that when bad things happen from switching, it involves 4T. Is 4T the chemical outlier? Has anyone figured out what bases the major brands are? Last question, and I realize this is subjective, but what is everyone’s favorite and why?

Sorry for the wall of questions, but we are trying to make a decision on what to use for next season. We have 4 engines under our tent and due to reasons, they are all using different oils. It’s annoying and takes up too much cabinet space in the trailer. The plan is to pick one and switch them all over this winter.

Thanks for any input!

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I’m not so sure about flushing or 4T’s chemical makeup. But, I run Redline 20WT Race Oil (5W20) because that is what my engine guy Don Holcombe at CMC uses and recommends. It seems like the oil most of the LO206 classes uses around here in Portland. I’ve had no issues or complaints. It is a good price for a quart off Amazon so I just keep using it.

It’s a CYA. Briggs/AMS Oil doesn’t offer any formulation information. Not uncommon, especially from majors. My guess would be that it is a PAO (poly alkyl olefin) which is an extremely common synthetic formulation in automotive and more compatible with many seals and plastics.

The rub is that not all synthetic oils are PAO. PAG (poly alkyl glycol), silicone, about 3 different types of esters, and even some highly refined mineral (crude) based oils are all considered “Synthetic” base oils. Some of those chemistries don’t play well together.

Per API, Group 4 and 5 base oils are synthetic. However, companies may brand some Group 3 (mineral/crude) base oils as synthetic if they offer the same performance. This was settled in a legal dispute involving Castrol I believe. It doesn’t meet API requirements, but it meets legal definition for marketing purpose. :man_shrugging:t2:

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Only time I have back flushed my oil is on a new block, I was amazed how much metal flake came out after the break in session. I did a back flushes in subsequent oil changes but it never saw anymore metal shavings; so I stopped doing it and instead popped for a magnetic oil filter plug (cheap insurance). Been working for me thus far . . . now I just change my oil and forego any more back flushes.

Here is a general overview that may help, https://www.eccarburetors.com/what-engine-oil-do-i-need-to-run-in-my-mini-bike-or-racing-go-kart

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Thanks for the link! Exactly the info and explanation I was looking for!