High temps only on highway speeds?

Hi guys, I recently have been experiencing something very strange. My VFR runs pretty hot at highway speeds and on acceleration but in stop and go traffic, temps are under control when the fan kicks in. She doesn't overheat even standing in traffic but once I start accelerating her temps climb pretty fast and the fan can't get her cooled until I come to a stop or idle her at a traffic light. Now I see above 109 degs C at speeds above 120km/hr.

I have flushed the cooling system, changed the fan, added a small delta fan to the right radiator, burped the coolant yet nothing.
No bubbling the overflow tank, she can idle for hours without overheating fan kicks on and off as expected but once she starts moving temps climb pretty fast and I have to park on the side for her to idle and cool off.

 

Can fans fun backward if the wiring is wrong or the fan is installed backward?

 

Wonder if you have a coolant flow issue, meaning a blockage/restriction or a coolant pump problem? Are the radiator cooling fins clear of debris, not bent or damaged and allowing good airflow through the core?
Not heard of your problem before!

 

That's a good head scratcher. The reverse normally applies, when no/low airflow at idle allows heat to build, but once running there is plenty of cooling air passing through the radiators. My 99 runs right around 78C at highway speeds no matter how hard I ride, and only goes above that in traffic.

The engine temp sensor is located on the engine block, but the thermoswitch for the fan is at the radiator. What does the engine temp show when the fan is cycling on/off? That might tell a little about the coolant circulation.

With the radiator cap off, can you see any coolant flow when the engine is blipped?

I tend to agree with Grum, I'd be a bit suspicious about whether you are getting decent coolant flow through the engine and rads. There has been at least one instance I recall when the drive to the waterpump has failed, and I have also seen the impellor fail through corrosion.

 

Temp shows 105 and cools to 94 C when idling but shows as high as 109 C at speeds with the fan on. I also tend to agree it may be a coolant flow issue. With the cap off, once the bike is started it flows then within a minute it starts to overflow. If I blip the throttle it spills so much coolant out. The temps haven't even gotten to 45 C. Note I removed the thermostat while troubleshoot just to be sure there is no restriction.

 

The fins are clear and cleaned. I can see through, though some areas are bent but not enough to cause problems lol. What I noticed really is that it seems the flow of coolant leaving the engine from the hose leading to the cap neck is faster than coolant being pulled in by the water pump? This hose gets really hard but other hoses aren't. WIth the cap off, engine still cold, it spills over immediately and when I turn off the bike it burps and coolant drops down into the radiator. Like air is trapped somewhere.

 

Actually that does sound like a coolant blockage from the radiator leading back to the pump, but not necessarily a pump fault. It's probably time to drop the hoses off the bottom of the radiators where these connect back to a T and to the pump inlet, and run some water through them. Maybe someone blocked a port with a rag to stop debris getting in?

 

Tried your suggestion now, the T joint is free of blockage and the hose leading to the pump is free too. Could it be from the radiators? I have tried reverse flowing each radiator and couldn't tell if there is a blockage. Is there a way to really flush out the radiators?

I also noticed that as long as the coolant level stays below the upper connecting hose from right to left radiator (running above the spark plugs) and just below the small air bleed hose, it doesn't overflow. It circulates normally. but as I fill up while engine is running and the level goes above the connecting hose, it quickly overflows.

 

I think I found the culprit! The left radiator lower lines seem to be clogged. Pulled it out and gently ran tap water through. Got flow in trickles and as I filled it up it flowed faster. I guess the lower lines are clogged? about 4 lines. The water just seats on one side and doesn't flow out. But if I flip the radiator upside down and do same, it flows smoothly through the upper lines.

Any ideas on how the unclog those lines? A pair of new radiators is pretty good money! Over $200!

 

I've used Prestone flush on my bikes and cars with good result.

https://www.amazon.com/Prestone-AS105-Radiator-Flush-Cleaner/dp/B00B99U088

 

I'd look for that, already bought some other radiator flush from the local store. says to run in engine for 10 mins. But I'd prefer a way of reverse flowing that radiator.

BTW, thanks guys for all the help. I still have one more issue lol. POOR GAS MILEAGE! Been struggling with this for months! Now it's worse, can't get past 8k rpms and it sounds like misfiring with a lot of popping from the pipes. Poor acceleration too.

 

Sounds like a good find at least. Is it possible to use a hose and just reverse flush the radiator (off the bike of course)? I would assume sediment will settle by gravity into the radiator so pushing the water the opposite way may dislodge it.

For the poor gas mileage, one thing to check is the fuel pressure regulator, specifically making sure the vacuum hose connections are tight, because if you lose the vacuum signal the FPR delivers higher than needed pressure. The FPR itself could also have a ruptured diaphragm which will let raw fuel leak through the vacuum hoses.

 

Lucky to find a used left radiator. Should receive it in a couple of days. I checked the FPR hose and it's dry, no fuel leak when the pump primes. I will inspect each hose for any leaks. I have also tried cleaning the injectors using a make shift adapter and carb-cleaner. They initially had bad spray pattern but eventual started spraying a lot better in a kind of split way, i guess to feed each intake valve?

 

Radiator replacement installed. Temps are back to normal
I still have to the lack of power and terrible mpg! Black soothe and smoke on the exhausts. I mean a healthy layer of soothe! Help!

 

By what you are saying about the Injectors, lack of power, poor fuel economy etc! I think to have them professionally cleaned and flow balanced might be worth doing.

 

Unfortunately, we don't have such professional services here, lol. best option for me is to order new ones. I checked the plugs and they all have a coffee brown colour and look the same. Not much difference in any one. So I swapped injectors put #4 in #1 and #2 in #3, cleaned the plugs and went for a ride. Came back and checked all 4 plugs. Same even brown color, none stands out like the culprit.

Makes me think an issue that affects all 4 cylinders, can all injectors go bad the same way?

 

How old are the plugs? Iridium plugs shouldn't be cleaned, wire brushes can damage the coating so they say. Plugs can cause very strange things, even if they might look ok. Fit a new set of NGK's IMR9B-9H.