TOPIC:

I'm with Nessism on this one. The oil level in the sump while the engine is running is what must be maintained. Find out how much oil the cooler system holds and add that to the amount needed to reach the full line on the window. If that higher level when the engine is cold and the cooler is empty causes problems, be careful to not rev the engine during a cold start. Monitoring that higher oil level poses a problem, but I think that could be solved. A dip stick would be easy to mark at the higher level.

A dip stick isn't possible on the early big fours. We're only talking about 1/2 quart here.
Steve

80B4 wrote: I'm with Nessism on this one. The oil level in the sump while the engine is running is what must be maintained. Find out how much oil the cooler system holds and add that to the amount needed to reach the full line on the window. If that higher level when the engine is cold and the cooler is empty causes problems, be careful to not rev the engine during a cold start. Monitoring that higher oil level poses a problem, but I think that could be solved. A dip stick would be easy to mark at the higher level.

Trying to solve a problem that doesn't exist.
Even with a cooler fitted and cold oil level on the high mark the oil will barely clear the sight glass when running which is still a hell of a lot higher than the pump pickup and under normal conditions the engine will run happily with the oil level at the lower mark when cold ( that's why there is a lower mark ).
There is more than enough oil in the sump even when the level is on the low mark .
If there was a problem with oil starvation when fitting a cooler to these engines it would have been found much earlier than 40 years after they were first produced by a bunch of random forum members with too much time on their hands.

Nothing is impossible if you own a CNC machine.
I will have to raise the oil level window the next time I machine a clutch cover. I may even design one that accommodates a dip stick

As far as I'm concerned this is a good subject. Before I parked my bike 20 years ago, I had a issue of oil starvation under hard acceleration. The oil light would come on, then go off so I kept a extra quart of oil in the bike to compensate for the oil cooler. Two and now a half years ago, as I was going through the engine, I went through the oil pump. I had three and made one good one. I removed the scratches in the oil pump cover, put it back together and when it was finally on the road, I couldn't get the oil light to come on again no matter how hard I nailed it. I may put a swinging gate in the pan but I don't think it is necessary now. I think it was just a weak oil pump.
Steve

I can appreciate that years of use suggest there is no issue with just keeping the oil between the sightglass levels on oil cooler equipped bikes. I will disagree that running the oil level a little higher will result in oil blowing out the breather and/or extra windage losses.

One other question I have is do the later bikes with coolers have the sightglass window a little higher up compared to the older bikes? I've looked at the 750/4 model bikes and the answer seems to be NO, but that's just based on photos I can find of the engine cover.

Nessism wrote:
One other question I have is do the later bikes with coolers have the sightglass window a little higher up compared to the older bikes? I've looked at the 750/4 model bikes and the answer seems to be NO, but that's just based on photos I can find of the engine cover.

The oil sight glass is the same height and position on all z650 and Z/GPZ 750 fours and 750 Zephyr although the 750 zephyrs sight glass is a larger diameter.
The GPZ and Zephyr have a coolers fitted yet share the same oil capacity as the non cooler models at 3.5 litre and so does the GPZ750 turbo.

Look at this Suzuki. Oil cooler is big.
www.motorcyclespecs.co.za/model/suzu/suzuki_gsx1100g%2091.htm

78X59mm. Hummmmm. 1127cc. Giving me ideas.
Steve

I ran an oil cooler in my kz750 H. I always put 3.5 liters. No problem so far.
I have more than 10k miles on the cooler.

Are different oil coolers stipulated to be fitted either with feeds up or down? Does it matter? ie, can one mount them either way and not encounter any issues? Also is there a formula for properly sizing oil coolers?

I tried to mount mine with the fittings up. Tank was in the way. I was hoping to keep the oil from flowing back into the sump.
Steve