Kawasaki VN750 Forum banner
1 - 3 of 3 Posts

·
Registered
2005 Kawasaki Vulcan vn750-a21
Joined
·
3 Posts
Discussion Starter · #1 ·
Greetings. I have a 2005 with about 15k miles and it runs hot but doesn't overheat and lose coolant. I have spent several hours looking at this topic on this forum and have tried most suggestions but the problem remains. Please bear with me while I lay out the facts...

Problem: Temp gauge slowly creeps up to near the max of the normal range after about 20 of riding at highway speeds.
53692


It started to do this last summer and continued into the fall riding season (I'm in Minnesota) when outside air temps were in the 40's. The problem continues after doing the following items.
  • Drain cooling system, fill with Prestone Flush and distilled water. Ran bike on stand for 15-20 min after warm up. Drain system. Drained fluid looked dirty but not terrible. It seemed to flow unrestricted out of the radiator drain. Fill with distilled water. Run as above and drain.
  • Disassemble system cleaning housings and head tubes. Cleaned overflow reservoir. Reassemble with new thermostat and hoses. Fill with Ethylene Glycol coolant that indicates it is safe for aluminum engines. Bled system at bleeder.
Problem continues so I removed the radiator and took it to a radiator shop where they pressure back flushed it. I was told brown crap came out and he indicated he doubled the flow through the radiator. He also removed the temp sensor at the bottom and cleaned it. I though "I've got this licked"! Not so. Still does it.

Other info:
  • The fan operates and comes on at the thermometer and cycles on and off as you would expect. Note: this observance is when running with no load on the center stand.
  • I changed spark plugs when I did the cooling system work and they were #8s (colder than spec). They generally looked dark like they were running cold so I replaced with the normal spec 7s.
  • Some subtle things: As stated it takes awhile for it to heat up. In fact it seems to operate at 1/2 scale for awhile (where I expect it to be) then slowly rises to the hot reading. When I park the bike with the temp reading high I can leave it running and notice the fan is not running even though the temp is above the thermometer. It starts in short order and cycles. The hot temp indication does vary a bit. It can read from just above the thermometer to close to the normal max while under the same highway conditions although it gives a consistent reading during any single ride.
  • The fan will run occasionally for 20 seconds or so after the bike is shut off. This seems normal.
  • The bike runs well.
Some of my thoughts:
  • Not likely a head gasket issue. This would pressurize the cooling system and force coolant out. Not happening.
  • One thing I did not do was pressure flush the motor itself. Maybe I should try another extended flush treatment and flush the motor???
  • The variability of the hot temp reading under consistent load conditions along with the variable temp indication of when the fan starts makes me question the operation (stability) of the gauge sensor. Has anyone found this to be a problem?
So there it is. I am very open to and grateful for any insights and suggestions you all may have.
 

·
Registered
Joined
·
9,364 Posts
Greetings. I have a 2005 with about 15k miles and it runs hot but doesn't overheat and lose coolant. I have spent several hours looking at this topic on this forum and have tried most suggestions but the problem remains. Please bear with me while I lay out the facts...

Problem: Temp gauge slowly creeps up to near the max of the normal range after about 20 of riding at highway speeds.
View attachment 53692

It started to do this last summer and continued into the fall riding season (I'm in Minnesota) when outside air temps were in the 40's. The problem continues after doing the following items.
  • Drain cooling system, fill with Prestone Flush and distilled water. Ran bike on stand for 15-20 min after warm up. Drain system. Drained fluid looked dirty but not terrible. It seemed to flow unrestricted out of the radiator drain. Fill with distilled water. Run as above and drain.
  • Disassemble system cleaning housings and head tubes. Cleaned overflow reservoir. Reassemble with new thermostat and hoses. Fill with Ethylene Glycol coolant that indicates it is safe for aluminum engines. Bled system at bleeder.
Problem continues so I removed the radiator and took it to a radiator shop where they pressure back flushed it. I was told brown crap came out and he indicated he doubled the flow through the radiator. He also removed the temp sensor at the bottom and cleaned it. I though "I've got this licked"! Not so. Still does it.

Other info:
  • The fan operates and comes on at the thermometer and cycles on and off as you would expect. Note: this observance is when running with no load on the center stand.
  • I changed spark plugs when I did the cooling system work and they were #8s (colder than spec). They generally looked dark like they were running cold so I replaced with the normal spec 7s.
  • Some subtle things: As stated it takes awhile for it to heat up. In fact it seems to operate at 1/2 scale for awhile (where I expect it to be) then slowly rises to the hot reading. When I park the bike with the temp reading high I can leave it running and notice the fan is not running even though the temp is above the thermometer. It starts in short order and cycles. The hot temp indication does vary a bit. It can read from just above the thermometer to close to the normal max while under the same highway conditions although it gives a consistent reading during any single ride.
  • The fan will run occasionally for 20 seconds or so after the bike is shut off. This seems normal.
  • The bike runs well.
Some of my thoughts:
  • Not likely a head gasket issue. This would pressurize the cooling system and force coolant out. Not happening.
  • One thing I did not do was pressure flush the motor itself. Maybe I should try another extended flush treatment and flush the motor???
  • The variability of the hot temp reading under consistent load conditions along with the variable temp indication of when the fan starts makes me question the operation (stability) of the gauge sensor. Has anyone found this to be a problem?
So there it is. I am very open to and grateful for any insights and suggestions you all may have.
I lean toward the temp sender being out of range, but working. It's not common on this bike but any temp sender can fail, or just be out of range.

I'd try to verify with a known accurate thermometer. Fan operation sounds normal, which makes me think operating temp is normal, the gauge just reads high. It may not actually overheat until the gauge is pegged.

You can always check the sender with an ohm meter.
 

·
Registered
2005 Kawasaki Vulcan vn750-a21
Joined
·
3 Posts
Discussion Starter · #3 ·
I lean toward the temp sender being out of range, but working. It's not common on this bike but any temp sender can fail, or just be out of range.

I'd try to verify with a known accurate thermometer. Fan operation sounds normal, which makes me think operating temp is normal, the gauge just reads high. It may not actually overheat until the gauge is pegged.

You can always check the sender with an ohm meter.
Thanks for your input Spockster. I'm going to head down the sensor road and see what I find.
 
1 - 3 of 3 Posts
Top