10w-40 is the factory recommend oil and 10w-40, of all the common oils, is a weight that is designed to handle the broadest range of heat variance in the world.

We do not recommend anything higher than a 15w-40. The flow rate and tolerances inside the GZ engine need something that will actually mate and lubricate. Cooling is accomplished through the fins, obviously, and the metal combinations found in the head.

If heat exchange is a real concern of yours, simply increase your main jet one size, enriching your mixture and running cooler - Do not leave your bike idling for any extended period of time - and just ride.

Simple and to the point. No extra plumbing for oil lines and potential future problems. Best of all it is cheap and easy......................like some of the gals in my past. :hehe:

A cool engine is an engine with a long life.

Not very many of you live south of my latitude. * not that I hold it against yah * 9~)

I'm thinking 20w50........It's hot around here.
And an oil cooler would be very.... well... cool...

I want i want

I would be a little leary of a 20-50 oil. The oil pump may not pick up a thicker oil when first starting the engine. Initial start up is the most critical time for any engine. Rotella 15-40 will likely work well and is designed to live in really hard working work engines in big trucks.
Keep in mind the GZ is used in many other countries where temps reach much higher than Texas and somehow survive.
Or just change oil a bit more often to prevent oil break down from heat. Always keep the oil topped up as it is used to carry away heat internally.

Welp. My 2000 suzuki gz250 owners manual does list 20w-50 as one of many viable options for warmer climates.
So now I'm curious...
Has anyone put 20w-50 in their bike and had the pump fail?? In a warm climate?
A weakness suzuki didn't know about?

I should have explained better. It is not so much a pump failure as a thicker oil not being picked up right away as soon as the engine starts turning over. If the manual says 20-50 oil will work then who am I to argue with Suzuki engineers who determine the specs and engine management. By all means go with the 20-50.

I have been thinking of going with a 20/50 oil as well as the temps here in Vegas have been consistently over 109 to 113 degrees the past two weeks. I guess I should check the manual for my own peace of mind. Great discussion.

15-40 is as high as I would go.

over 15w-40 is a waste of gas and lost of power because the oil pump use more power from the engine to move the oil.
this is why the new cars move to 5w-20 ore 0w-20

Welp. I got a long log of gas mileages that I've been keeping since I got this bike ten weeks ago.
I'm on my second oil change now and I have two of my three oil filter multipack left too.
(I'm changing often to clean out the engine.)
Imma look for some legit 20/50 motorcycle oil and switch filters again in 2 weeks to a month,
new filter and all, then compare any changes in the gas mileage log after that point.

My prediction is the mileage will be practically unchanged and the benefit to the engine in
a hot Texas summer is obvious as the owners manual acknowledges.

However. I will be honest. If my mileage drops or if I blow up my oil pump I'll report so.