Trying a different rad cap

Hoping to stop coolant from spitting out when overheating ('01 WR426), trying a Stant 11233 I got at auto parts store (Rock Auto has 'em for $6.18).

Says 16 pounds on cap, hoping that's higher than stock cap.

There is a reason the stock cap is rated where it is. I don't think I would be messin' with that!

There is a reason the stock cap is rated where it is. I don't think I would be messin' with that!
I agree. First figure out why it's overheating. If it's just slow technical terrain, try different coolant. Straight distilled water transfers heat better than anti-freeze (i.e. Prestone, Zerex, etc.). Water wetter or other surfacant helps to increase that heat transfer. I only use just enough anti-freeze to achieve my desired freeze protection. In the summer you don't need any, just remember to change it before it gets cold. If that doesn't work (and assuming you don't have an underlying problem) Evans NPG-R is a waterless coolant that has something like a 400 degree boiling point. That will definitely stay in your rads, but it's expensive at about $30 per gallon for the NPG-R and another $30 for the required flush. You won't need any pressure cap if you use that because it doesn't need the higher boil temps provided by the pressurized system.

The stock WR450 cap is 15.6 psi and I would guess that the 426 cap is the same so you probably haven't gained much. Baja Designs sells a 1.6 kg/cm cap which equates to 22.76 psi. Don't know much about it but I know a lot of the hard core off-road guys run them. As far as running straight distilled water I would be concerned about corrosion protection and seal failure since one of the things that coolant provides is lubrication for the water pump. Also most "distilled" water you buy today is made by deionization. Unfortunately de-ionized water has an affinity for metals that will cause it to seek to "re-ionize" by extracting ions from the metal (laymans terms = corrosion). It's not a problem when mixed with coolant since the coolant "re-ionizes" the water but by itself it can be a problem.

PDBBLUE is right running straight water is a bad idea. the coolant first fights corrosion (dissimilar metals need help to fight electrolysis) second is seal and mechanical lubrication then third is boil and freeze protection. if the cap you have is more than a year old replace it replace the coolant at least annually. these two things will be a good start. Try a good motorcycle coolant I don't want to start a crazy thread on what coolant to use. any local auto or radiator shop can test your radiator cap to see if it is holding the correct pressure you would be surprised how often they fail to hold all the pressure even when new.

WATER WETTER will provide your corrosion protection without reducing the heat transferability like glycol will. Watch the demo.

I did install Water Wetter at same time as cap change, hope it all helps. Only have trouble with spitting coolant in tough circumtances - thought many here with WR's would have also. I even pack a strong plastic bag to carry water from streams to fill radiator when riding in the mountains.

When I had my old KLX650R, it also would get hot and spit coolant in certain situations. I was told a higher-pressure cap (got one for a 2001 KX65), would help. Installed it - never had trouble with ovrheating again.

If stock is ~15, the 16-pound cap I installed may not be enough:,hi%20pressure.html

There is a reason the WR comes with an overflow resevoir, do you still have it or are you one of these guys that has taken it off to "shave some weight"? Depending on the riding you do it might be in your best interest to put the resevoir back on....... I do alot of "pack and carry" type rides here in Western WA and while all my buddys are dumping water into their YZ's I just sit and watch while I drink the cold beer I had sittin' in my back pack :thumbsup:

I have run every coolant combo except the EVANS NPGR, and I will try that sooner or later, but every one of them has boiled over in certain conditions. To date my best luck has been with Engine Ice but I hear the EVANS out performs the Engine Ice :thumbsup:

My 2 cents worth is to run the stock cap with the overflow resevoir in place.

Check the clearance between your exhaust header pipe and the radiator. After a few tumbles my rad got bent in towards the pipe a bit, closing the gap a bit. My bike started overheating more than usual and I used an infrared camera to see if I could find a problem. The bottom reservoir of the right rad was being heated by the pipe and the coolant was picking up heat rather than dumping it as it passed through. I opened the clearance up a bit by pulling on the rad and adjusting the pipe and then both rads showed the same temperature. In the IR pic everything black is cooler than the set temperature range and everything white is hotter.

I find the WR's run hot, but mine seemed to get hotter with age (unlike most things). It's probably a combination of things like the rad cap spring weakening, old coolant, slightly bent rad, all adding up.

Do you remember your bike boiling over as much when it was new? I don't think mine did.


I still have the coolant reservoir on the bike, wouldn't think of taking it off. Might relocate it if installing side-panel gas tank tho...

I'll check the exhaust pipe to radiator clearance, good suggestion. Bike doesn't overheat anymore now than when new, just according to riding circumstances.

In my experience it's pretty normal to boil over if your running hard and not moving much (like flailing around in a bunch of rock's for example). Lots of engine heat + no airflow = boilover!

It's happened to me a few times. With or without the reservoir doesn't really make much difference except you don't actually loose the coolant with the reservoir but the engine gets just as hot. Run with it on my dual sport and run naked on the sticker bike.

a leaky head gasket can cause over heating also. The compression from the motor will pump air into the cooling system causing excessive pressure and poor circulation.

You can notice if thats the problem pretty easy as your coolant will be dirty and foamy.

anti freeze not only does what has been mentioned, lubrication, anti corrosion, and freeze protection, but also increases the boiling point of the fluid. The pressure from the cap also increases the boiling point of the coolant.

Your pump also needs to be doing its job. If your impeller or volute is damaged at all you wont have the circulation needed.

Did this mod this weekend:

"You CAN make a higher pressure cap!

(Yep! I'm giving away a BIG secret that we found out in 1994!)

1. Buy a "Stant" brand, #11233 cap. It has a BROWN spring in it that is just shy of 1'/25.4mm diameter. Actual measurement was .965"/24.46mm on the one that I'm measuring right now. It's the only "Stant" radiator cap spring that is brown AND ~1"/25.4mm diameter (if you forget the STANT part number and have to measure every Stant cap on the rack). It's almost always in stock in automotive supply stores.

2. Take the STANT cap. Get pliers, diagonal cutters, needle nose and attack the STANT cap. You WILL be amazed at how some parts can be designed to be assembled quickly and easily and are nearly impossible to have accidentally come apart.

Anyway - get the brown spring out.

3. Take your stock cap. Now take the brown spring and spread the "tail" of the spring by hand, just enough to work it around the spring retainer on the stock cap. You'll have to lever the end tail over the cup to avoid damaging the rubber gasket. Presto - 21 to 25 psi cap - just like all them car guys use!"

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