Honda Rubicon "overheating"

[yanmars]

My 2005 Honda Rubicon runs fine when it is cold. When it gets warm it loses power. Sometimes the fan comes on and sometimes not, more often not. I think if the fan operated correctly it would not get warm. The radiator is not clogged, good antifreeze etc. I do not think any hoses collapse, all components are newer.
I have had this checked out more than once by trained Honda personnel. Could I just get a manual switch or have the fan run all the time? Normally no trouble in winter but trouble in the summer. Thanks

 

[SpudHauler]

I would look to having the thermostat replaced.

While the system is open, flush it completely and put new antifreeze.

If the drive belt and CVT system has not been serviced in a long time issues there can cause problems. Mainly worn parts make it act like it starts in second gear and you are always a gear to high. I know it doesn't have gears but each ratio change between pulleys is like a gear and a worn belt can put you in a situation like being in 1 gear too high. Engine works harder all the time and heats up.

Other checks would be to raise four wheeler and make sure all wheels move by hand freely, no sticky brakes.

 

[rmk700]

The fan is not suppose to stay running. Mine only comes on when I'm working it hard. How do you tell it's overheating?

 

[rmk700]

I would look to having the thermostat replaced.

While the system is open, flush it completely and put new antifreeze.

If the drive belt and CVT system has not been serviced in a long time issues there can cause problems. Mainly worn parts make it act like it starts in second gear and you are always a gear to high. I know it doesn't have gears but each ratio change between pulleys is like a gear and a worn belt can put you in a situation like being in 1 gear too high. Engine works harder all the time and heats up.

Other checks would be to raise four wheeler and make sure all wheels move by hand freely, no sticky brakes.

Has no belt, CVT. runs off a hydrostatic trans. Awesome tranny IMO

 

[SpudHauler]

Thought it had that tranny but something I read said CVT. I was wrong for sure.

Your oil and filter changes changes this oil too or is it separate.

Try changing that as well if not.

Sometimes a little routiine maintenance can solve problems.

True, no engine is designed to run fan full time. Fan is backup for extreme heat situations.

Over sized tires hauling big loads at low speeds would be a time the fan should be coming on to help in cooling the engine.

Still think sticky thermo is the most likely.

 

[crazyal]

Do you have one of the hand held infrared temp meters? Harbor Freight sells them pretty cheap. If so I would check a few points to see what the engine is running at. The manual should tell you at what point the fan should come on and it should be easy to locate the sensor so you should be able to tell roughly if the sensor is working correctly.

 

[dusty3030]

Remember the engine oil is the tranny oil too.
Are you running recommended oil?
My Rubicon when it was cold would stall out until it warmed up and the oil thinned.
Also change the plug if you never have with the oe NGK iridium that comes in it.

 

[yanmars]

I use just the Honda oil that they recommend.

 

[dusty3030]

Cool, determine now is it overheating and engine loosing power or is it something else.
I think it will end up being something else. The transmission on these is really a variable displacement pump using the engine oil as the fluid.
I think you are chasing a fix in the wrong direction. Need to make sure the transmission is operating correctly - try it in manual mode and in auto modes 1 and 2 etc and see if there is any difference.

 

[dusty3030]

Also, on looses power, please give us more detail on what that means - ie what running under load, no load, pulling something, going up a hill etc.
Do the engine RPMS drop or does the engine run fine and the machine is unresponsive etc.

 

[AaronS]

It looks like your original question was never answered. Yes....you can rewire the fan and install a switch that would allow you to turn it on when you wanted. As others have hinted though, this would only be a bandaid and not a cure. If you're positive that the radiator is clean and it is full of good antifreeze, then check the oil like mentioned above. One helpful tip that I learned on my 2001 Rubicon is that the threads from a soft drink bottle match the threads on the oil fill hole, so you can make yourself a hands-free funnel.

 

[yanmars]

Sorry about the late response. The antifreeze is nearly new, no crud in the radiator and water wetter added. Fluid not down in the radiator. The engine/trans oil could be down a pint.
As regards losing power. Once it runs about 10 minutes I can feel the extra heat radiating from the engine. It will start to "growl" a bit. On the flat it will run but when it gets to a 50 foot hill it does not have enough power to make it to the top. I will have to stop and park it. An hour or so later when it is cooler I can then start it again and get it to the top of the hill. Two qualified Honda trained techs have not been able to cure the problem.
One did tell me it is on the low end of the compression, it "supposedly" had the engine rebuilt before I got it but no verification on this and what and how well this was done and by whom is in question. Never any trouble starting or trouble in the winter when it is cool. Just not a summer machine. Hope this helps a bit.

 

[SpudHauler]

How low is low? Compression on this machine probably should be in the 140-150 lbs new and with age can fall to about 125. Anything lower would mean pretty poor performance.

It's time to pull it apart and investigate, there is no way a good running engine would act like you are describing. And with an unknown repair and these problems after, get the tools out.

A new spark plug will not fix this issue.

Just another thought, if cold or after it heats up and has little or less power, does it still roll easily if in neutral and you were to push by hand the machine forward or backward. Just making sure some brake system is not heating up and trying to apply itself.

Sorry for the bad news.

Good luck with the repair.

Best guess, sloppy unknown rebuild.

 

[SpudHauler]

Another thought.

Just in case it has not been checked, have the valves adjusted. Could be valve lash too tight.

And retest.

 

[yanmars]

Thanks for all the helpful suggestions.

 

[yanmars]

In thinking about the low compression, any chance the break in before me was not done right and the rings did not seat properly or varnish over or valve lash/adjustment might be a factor? I hate to put more money in it but it does not serve me well with the way it is either.

 

[SpudHauler]

Yanmars,

Not sure of your abilities but a quick check of valve clearance would be useful and not too hard to do.
I owned a TRX450ES 2000 model which is a similar engine to yours and did my own work on it.
Do you have a manual?
Anyway, here is a quick how to:
1-remove tank and side covers so you have access to the top of the engine
2-hose off all the dirt and grime and blow any dust or dirt away (very important step)
3-remove spark plug
4-remove valve cover
5-to get engine to TDC (top dead center on compression stroke) do the following.
- using the pull cord slowly rotate the engine until you see the intake valve move down or open, these are ones on the carb side of the engine
- then with a straw, poke down the spark plug hole to feel for the top of the piston.
- using the pull cord, slowly pull the engine over until you feel the piston come to the top or highest point
if it starts to go back down (you feel it on the straw) then stop. your close enough
6-using a .006th feeler gauge check to see you have that much clearance on all 4 valves both intake and exhaust
- if a .005th will fit you are close enough
- if a .007th will fit but .008th will not fit that is okay too
- anything between 5-7th will work, anything else means they need adjusting

If you have a hard time finding TDC, just try the above method a couple of time to get the feel for how much to pull the pull cord and when close to TDC you will have loose intake and exhaust rockers. Any other time one or the other rocker will be tight.

There is a plug on the side of the engine that can be removed with timing marks that can be used as well.

I'll look for an online manual, have one for a 350 that is similar but might be confusing.

Just curious, does the head gasket seem to be leaking? Any oil leaks?

If the valves are too tight this may be your problem so find this out is important.

Good Luck

 

[yanmars]

I have the Honda Rubicon owner's manual, not here but probably 200 pages or more. Thanks for the information.

 

[SpudHauler]

You know you could try running with no thermostat, just to make sure it's not overheating and seize up.

FYI
The manual I saw just showed adjusting the intake valves. The front cap is the exhaust valves. You need to check all.

 

[azranger]

Try checking the oil temp sensor wire and see if it is grounding out on the frame, it is usually near the bottom of the crankcase. Also have you checked the ecm, .. rectifier regulator? just my .02