GPZ750R Ninja

Hi,

Have recently acquired an 85 model of the GPz750R and the oil cooler is
burst.

It has been bypassed by the previous owner and I was wondering if it is
ok to drive in this condition (given that it is being ridden in
Scotland!) and also if the oil cooler from any other bike will fit it?
(The GPz600 from the same year looks to have a similar cooler fitted)

Hope you can help

Dave

 

Liquid-cooled Kawasaki GPZs had a reputation for running hot and
occasionally dumping their coolant - I'm assuming this is the
liquid-cooled 750R, by the way - so I would replace the cooler. The
unit from the GPZ900R is identical, as the 750 is nothing more than a
sleeved-down 900.

If you've got the air-cooled 750, then I'd still replace the cooler,
but no idea what fits.

 

Thanks for the reply

Yup its the liquid colled variant. Was askinhg about alternative oil
coolers as there are none available from breakers from the 750 or 900,
but the gpz600 unit looks very similar

 

I've been to Scotland in June. It was very windy and cool in Edinburgh.
I got rained on in Fort William and caught the beginnings of one of the
nastiest colds I've ever had..

You might be OK in Scotland without an oil cooler, just watch your
water temperature gauge to see what it's indicating.

If it has no numbers, you can calibrate the gauge by immersing it in
boiling water. Consider the altitude you live at to see what
temperature water boils at there.

If you don't have a variable output power supply, you'll need to use
the engine's alternator for a power supply, so you'd have to remove the
temperature sender, plug the hole with a plug of the correct thread and
run a power wire and a ground wire to the sender and rev up the engine
to see what the gauge indicates while the alternator is producing
normal charging voltage.

And, since you probably don't have an oil pressure gauge, you should
acquire one to see what the oil pressure is when the engine gets as hot
as it normally does riding around in low gear in the Highlands...

Check out the shop manual to find out what the minimum acceptable oil
pressure is when the engine is hot.

Don't want to go through all that hassle? Buy the correct oil cooler.

But, it's YOUR motorbike, and if you want to *guess* what would work
and what wouldn't work, go for the bodge job you're thinking about...

There's a very good reason why you'd want to replace a burst original
equipment oil cooler with the correct original equipment cooler.

It's the amount of pressure restriction at the cooler inlet hose, and
the internal restriction of the tubes inside the cooler element.

(Don't ask how I know about the pressure restriction requirement.)

The oil cooler doesn't cool ALL the oil at once, all the oil doesn't
flow through it, only *part* of the oil passes through on each pass.

There's probably a restrictor where the oil line goes to the oil
cooler. That keeps most of the oil from going to the cooler, and it
keeps the critical *oil pressure* to the *bearings* at the correct
level.

If you install the wrong cooler just because you can find a cheap one,
the oil temperature might rise too high if there's too much
restriction, or the oil pressure may be too low if there's not enough
restriction and you might wipe out the bearings in the bottom end and
trash the entire cylinder head which has NO bearings in it at all!

(If you do buy a used oil cooler from a salvage yard, flush the damned
thing out. Gawd only know what kind of crud might be lodged inside.)

The engineers who designed your oil cooler system were *fine tuning*
the total cooling ability of the engine so they could jet the
carburetors as lean as possible to meet pollution requirements.
Lean-jetted carbs make the engine run hotter at very low RPM. You can
do quite a bit to keep the temperature down by screwing the idle
mixture screws counterclockwise half a turn or so, or by installing
idle jets that are one size larger than standard.

Re-tuning the carbs to make the engine run cooler is fuel-inefficient,
and, with the price of gasoline as high as it is, you might not want to
tweak the carbs, it might just be more cost-effective to buy the
correct oil cooler for that model...

Can one say that the typical modern sportbike with a liquid cooling
system, and oil cooler, and a thermostatically-controlled fan is really
a
liquid-cooled engine?

No, it's not. Ultimately, the coolers exchange heat with the
atmosphere.
In the end, your engine is as air-cooled as anything with a bunch of
fins and no fluids exchanging heat with the surrounding air.

Kawasaki and Yamaha have been building engines that run so lean at low
RPM and get so hot, the variation in water temperature is EXTREME, from
running at 180 degrees F to running up around 260 degrees F in a matter
of a few miles of slow traffic.

Oil temperature is closely tied to coolant temperature. If you're using
an inexpensive mineral-based oil, the maximum temperature that you want
the oil to ever get to is 240 degrees F. When mineral oil exceeds 240
degrees F, cut the oil change interval in half.

My Suzuki with the Lockhart aftermarket oil cooler ran at 290 to 300
degrees F oil temperature. I changed my mineral oil every 100 miles
when I was racing.

If your oil temperature gets up around 250 to 260 degrees F, you should
be changing mineral oil every 1500 to 2000 miles...

I tend to think of the liquid cooling system as more of an *attempt* to
hold engine temperature below the 350 degrees it would normally run at
if it was an air-cooled engine.

But, I live in a hot dry valley where the average high temperature
reaches 99 degrees F every day for the entire summer. There isn't much
traffic congestion here, so my coolant temperature stays in the 200
degree range during slow riding. The fan occasionally comes on during
slow riding. But my Yamaha has one of those tiny cylindrical oil to
water coolers behind the oil filter. It doesn't do much to cool the
oil, so far as I can tell...

 

Dave fumbled, fiddled and fingered:

Can you not get a car radiator specialist to repair your existing oil
cooler core?

--
Steve Parry
K100RS SE & F650
and a 520i SE Touring for comfort

(not forgetting the SK90PY)

http://www.gwynfryn.co.uk

 

That occurred to me. Or just look up Yellow Pages for the specialists
and get a custom-made one built. I bet it'll be cheaper than a new
Kawasaki item.

 

Hi,

Thanks for the info, advice and your time. Will try to see if I can get
a local specialist to repair the existing one.


Thanks again

Dave

 

Damn fine. Name 'em, then.

 

UPDATE:

Took the chance and sourced an oil cooler from an '85 GPz600: Identical
in all respects other than the protective grill is slightly longer on
the 600. This initially fouled on the mouning bracket but simply
bending the grill round the ends of the cooler, slightly, allowed it to
fit.

GPz600 hoses were of no use and the ones on the bike are suspect.

Kawasaki wanted about £116 per hose, a breakers quoted £25 for both
BUT phoned Goodridge directly and got a set of new hoses for just under
£22 including VAT and delivery! How good is that!?

They were out of stock for the hoses but at that price think I can wait
a week.

Thanks again for all the help and info.

Dave