Measuring Radiator Flow

Is there a DIY method to measure the flow-rate of coolant through a
motorcycle radiator? My bike is 12 years old and I'm wondering if
there's been enough scale build-up in the radiator fins to reduce flow-
rate and the water-cooling efficiency of the radiator. I've looked in
the bike service manual and it gives no information on how to test for
flow rate. TIA for any tips or suggestions.

Manjo

 

What kind of unforeseen, mysterious problems does your
bike surprises you with?
Temp needle in red zone?
You get hot knees?
It steams all the way?
It burbs when you switch it off?

In other words, if there aren't any problems,
why do you search for a cause?

Just think for a second. Why would the manual
not define a flow rate, let alone how many miles
you may ride before you need to check it.

Rob.

 

Probably also be OK to do a radiator flush
and throw in new coolant if in doubt. Might
be way less trouble than trying to measure it.

Never owned one of those newfangled water
cooled bikes myself, so take it as pure speculation.

 

Hi Rob,

Thanks for your thoughts. Perhaps you could help if I give you more
information.
I ride a V-twin with 125k miles (117k miles are mine). In warm
weather (above 80 degrees F) the bike will stall out at stops while
the rpm's fall under 800 rpm.

I've rejetted the carbs, sync'd the carbs, set and reset the idle
speed, cleaned the air filters, confirmed the cam settings, changed
the fuel filter, checked the fuel pump flow, etc. I'm pulling the
engine this winter and checking the bore and heads. I have to
disconnect the radiator again and can easily test it standalone. I'm
looking to eliminate as many heat causing and heat dissipating
possiblilities as I can while I have the engine out and apart. Low or
slow coolant flow could cause an overheating problem. What are the
other possibilites to check?

Thanks, Manjo

 

I'd check the compression, ignition timing, and make
sure the head gaskets were not leaking.

I normally set my idle above 1000 RPM. 800 sounds
low and I'd expect mine to stall at 800 too.

Can you check the oil and water temps ?
Are you certain it's overheating ? Onboard
temperature guages are something I really
appreciate.

 

If you are gonna pull the engine, pull the radiator too and have it boiled
out.
That should set your mind at ease.....about the radiator anyway.

 

Rob Kleinschmidt wrote that he never owned a water cooled bike
thus 'speculates' it would be good to flush the radiator.
Well, this is sound advise, no matter what state the radiator
is in.

Myself, besides a couple of air cooled, I only have owned 3 water
cooled bikes. The first was 18 years old, second bike was 20, and
my current one is almost 25 years.
None of them ever showed any scaling of the radiator.

You now describe your problem as: at warm weather, bike
drops below 800 revs, then stalls.

Idle at 800 revs is pretty low. Is that what your manual says?
The bikes I have had all were around 1100-1300 revs.
The on-board 'revcounter' (if any) usually is crude
and should not be used to adjust idle.

I think the radiator has nothing to do with your problem.
If the bike has a temp-gauge, it should read between
the red lines, also in warm weather. If it does not,
then the thermostat could be defective, and there should be
a description on how to test it in your manual, or
the fan, or thermo contact, or wiring, or even the water pump
could be defective.

To set your mind at ease, check the piping for scaling. Easy
to check visually. I bet you won't find it.

Your idea is: "Engine stalls because engine gets too warm"
But, if warm weather really is the cause, then every air cooled
engine would have the same problem.

Personally, I'd search in the fuel/carburettor area for the cause
of your problem.

And, since you're unmount the radiator anyway, take
Rob Kleinschmidt's advise. Flush the thing. If it does not
help, it will not harm anyway.

Rob.

 

Rob and Rob,

Thanks for the ideas and logic.

I will have the radiator flushed boiled out.

I mislead on 800 rpm. I have the idle set at 1,000 rpm and as the
outside temperature approaches 80 degrees F, the bike's idle speed
decreases and the bike runs rough at stops and as the heat increases,
the engine will stall. I have never had a problem re-starting the
bike. When this happens in stop and go traffic, I'm especially
careful to down shift so that at just before a full stop, I have run
the bike in 1st gear for several yards. This tends to reduce the
stalling some. This has led me to also consider the fuel system as
the possible source of the stalling problem (vapor lock??).

I ran a leak down test on the bike myself and had less than 2% overall
compression loss. This was after I had the cylinders honed and
installed new rings and checked/lapped-in the valves.

NOTE: Last spring I installed and broke in new rings/honed cylinders
"easy" by riding under 50 mph over 500 miles. I'm thinking now I
should have broken them in hard varying the speed between 40-60 mph
over 500 miles to better seat the new rings. I say this because I see
a lot of carbon build-up on the cylinder heads that I remove once in a
while with Sea Foam end. The carbon has also been a concern in that
it may be causing pre-ignition at idle enough to cause stalling? END
NOTE.

When I get the heads and cylinders off, I'm borrowing a bore gauge to
check the cylinders for out-of-round that may be allowing oil to seep
around the rings at high speed and burn-off on the piston crowns
leaving the carbon build-up. I'm also going to ask the machine shop
guys to check the heads/ valves just in case oil is leaking around the
valve guides (I installed new valve seals last spring).

I feel I'm intimately familiar with engine by having taken it apart
and refurbishing/replacing many parts, but I lack the real shop
experience of having fixing many different bikes with the same
problem. I also have no fear of pulling the bike/engine apart and
trying proposed solutions.

Thanks, Manjo

 

That symptom has me really baffled. Normally my idle will
increase as the engine gets hot. I suppose vapor lock might
be worth checking for. I'd also wonder if you might be running
way too rich at idle, causing it to bog down. When it gets to
this state, you might shut it down and check the plug color.

 

WHAT, AGAIN........?????

You do have a one track mind, don't you?

Here's my take: You are running RICH, causing the carbon buildup (how
paranoid does one have to be to actually MONITOR the carbon buildup in the
chamber ;-) ...).
As the engine heats up, it "likes" to be a little leaner. If you are way
rich, it will do exactly as you describe. Engines do not like to be rich
when hot.

I think you need to check your mixture......with an exhaust gas
analyzer....and then fix the carbs. or intake restriction or whatever it is
causing the rich mixture.

I cannot in my wildest imagination see how taking the heads off yet again
will help anything.

 

Indications are that your idle mixture is incorrect.

Check your carbs to be sure that the throttle butterflies are covering
the idle mixture ports when the idle screw is initially set.

This will require a 'bench synch' with the carbs off the bike. When
you look at the butterflies from the engine side they should be
covering the transition holes.

Also, check your float height. The float height measurement should be
within plus or minus 1mm of specification. A smaller measurement means
that the fuel level is too high and the engine runs "soggy" at idle.

Float level measurements are taken from the bottom of the float (which
is on top when the carb is upside down on the bench) to the aluminum
gasket surface, not the gasket (or o-ring, in case of a Kawasaki).

Furthermore, check the brass needle jet (the tube that the main jet
screws into) to see it the needle has banged against it and made it
egg-shaped.

This can happen in as little as 5000 miles on semi-downdraft carbs
mounted on motorcycles that vibrate a lot.

Lastly, when the engine is warmed up, put your finger over each
enrichener inlet hole in the carburetor mouth to see if that makes the
RPM
change. The enrichener hole is the larger of two holes in the inlet
mouth.

If the enrichener plunger is leaking air, the engine will act like
it's on the choke all the time.

 

I hate to be too simplistic, but I hope you're in Neutral when you're
at a complete stop, if not, maybe the Clutch is dragging a bit to make
it stall?
Bg

 

I will check this shortly, although the symptoms only appears at
temperatures over 80 degrees F. I've taken the clutch apart several
times and I'm careful for undue wear and to torque everything to
spec. But I will go over it more carefully to be sure. Thanks.

Manjo

 

Jack: I am loosing oil at the rate of about a quart every 800 miles.
The compression test bumps up fine. A leak down showed less than 2%
loss compression loss. It may be a valve guide problem that I intend
to check shortly.

Jack: No smoking, but when I'm leading my wife says she does smell
oil burning from time to time.

JACK: Extensive changes to both. I've taken out the EPS duct work
and surge tank and have K&N filters mounted directly on each carb
intake port. The exhaust system is a Jardine set that's nearly
straight pipes. I've rejetted with larger main and idle jets to
enrichen the air-fuel mixture to match the higher air volume.

Manjo

 

KEN: (sigh)

KEN: I'll take a shot at that. Manjo

 

OK, so how many times are you going to take the clutch apart before you
realize that it is NOT the problem???

In addition to the already mentioned potential fuel system problems, you
could also have a vacuum leak that is showing up when "parts" expand as they
get hot. Pay particular attention to the boots between the carb(s) and the
engine intake.

 

Grrrrr......It never occurred to you to mention ALL THAT when you first
posted the symptoms of your problem?? Crap.

 

Thanks. I'll be sure to check the boots, again.

Manjo

 

Sorry about the crap. This thread started out as a radiator flow
measurement question and evolved into a list of very helpful
suggestions and identification of other possibly contributing
elements. I've tried to provide as many details as possible at any
one time without distracting the reader.

I have everyone's suggestions gathered into one document that I will
use as a guide as I work through the bike.

Thanks.
Manjo

 

And just for laughs, check the compression in each
cylinder. You can spend lots of time fiddling with carbs
and ignition when the real problem is one cylinder
pumping way better than the other.

If one cylinder's pumping poorly and you try to compensate
for it with tuning, you can confuse yourself pretty thoroughly
and induce some very odd behavior.