Overheating a 400E?

I had a problem with my bike heating up on a bad hill the other day. To make a long story short, it was one of those "there's bound to be another way out once we get to the bottom" situations. Not!!

The only way out was a really long steep hill that is nothing but loose dirt, head sized rocks, lots of curves and no way to get a run at it. After watching my buddy lock his atv in 4 wheel drive (there's something unfair about that) and claw his way up, I tried it. About 50 minutes later we managed to walk/lug/ride/curse/push/pull mine to the top and proceeded to collapse. I honestly thought we'd have to winch the bike up the hill at one point. It was that bad. Almost too steep to stand on.

Anyway, the whole time this was going on, I was running the bike pretty hard with a LOT of wheelspin and very little movement. Towards the end of it the rad tank was getting full and it started to literally pour steam out the overflow hose.

Has this happened to anyone else? The bike never lost power or threatened to quit, and once I got some air over the rad's it cooled right off and sucked all the antifreeze back in.

Is this just something that happens or should I be checking for a problem? I've never seen any bike (much less mine) spew steam like that before. It looked like a fog bank under the bike :)

I've only boiled mine once. Same program. I've heard the heavy duty cap off of a late model kx500 will will help alot. The stocker is a 1.1 bar. I think the kawasaki unit is 1.4... Anyone out there know about this?

Yes, someone posted a part number, maybe NAPA for a maybe Toyota cap that was 1.6 bar...Got the data home, but not here...anyone with the info in hand?

I reposted some Stant part numbers I got from from a previous post and they all turned out to be too big to fit. I did not see them but that is what I was told after a friend ordered some at Checker. I went to NAPA and the counter man looked up the small caps and most have PSI ratings that are lower than the 1.1 (15.7 PSI) cap that comes on the Suzuki. The highest pressure cap he came up with out of his book was 16 PSI PN 703-1406. I bought one for my buddies bike for around $10. His rubber seal was getting eroded from boiling several times. I am happy to say it worked and he is no longer ribbing me for the bad part numbers I got from earlier posts.

I was in a checker the other day and browsed the Radiator cap section and they did have a 16 PSI Stant cap For $6. I bought one just for a test and a spare. PN 11233. It fits but I have not run it for a test yet.

Boil over and overheating are two different things. If is spews and you let it cool and there is still plenty of water in the radiator then it was not overheated enough to do any damage. Heck if a air cooled bikes temperature was ever taken it would be a lot higher under normal conditions. If you run the bike with all the water boiled out then it will torch the engine. That is what can happen when the waterpump hose gets punctured or a small leak goes undetected.

I do know the Suzuki cap is good enough for most applications and water wetter added to a fully purged system including half full tank has kept my Drz400E from boiling over when other bikes of all varieties boiled under exact same conditions.

Higher pressure may blow the hoses or radiator according to the Suzuki manual.

The formula for the pressure is in the book page 5-5.

1.1 kgf./cm2 is what the cap is rated at. The test range is .95 to 1.25 and that is supposed to = 13.5 to 17.8 p.s.i. That converts to about a 14.23 conversion factor if you want to go hunting for other caps. Maybe I got lucky and my cap is at the high end of the range and others are at the low end.

I just checked my Honda CR250 service manual and it says the 1.1 cap means kPa. The test range on it is 16 to 20 psi. The conversion numbers in the book work out to about 14.25 to 14.5 depending how they rounded. It will fit the Suzuki also.

I still think the best bet for a worn out cap is a 16 PSI from the auto store for 6 or 10 bucks and a $8 bottle of water wetter will do 4 bikes.

If you are confused do not feel alone. The above info is probably pretty reliable as I cross referenced the Honda and Suzuki service manuals.

If Kawasaki has a 1.4 cap then it is probably in the 20 PSI minimum range 1.4X 14.23= 19.9 PSI. Their service manual should show the min/max range and if I was going to order an expensive cap I would want to see the those max numbers before making that choice.

I hear they work well at altitude but have know idea how the numbers are affected by partial atmospheric pressures.

I do know my Suzuki never spewed at any altitude when others did and some were Kawasakies.

DDACT I have boiled my E countless times. Usually when exploring no-track areas with lots of fallen timber. I gave my fuel screw an extra turn. This not only helps with the off-idle stumble but the richer jetting seems to reduce the boil-over problems. On a side note you mentioned lots of wheelspin on your hillclimb adventure. My experience with really steep, loose hills with the E is that it will dig in and spin if you lose momentum. My greatest struggle with the E is if I am in too low of gear = too much torque for available traction = wheelspin and no traction. My solution is to upshift and modulate the power with the clutch and let the engine chug to the top. Much like trying to climb a hill with a small displacement two-stroke except keeping the revs much lower. Also the clutch-low revs method is a lot safer than wheelspin in case the bike ever hooks up on some solid rock. The bike will be up and over before you know it.


Yes, the same thing has happened to me. I don't think it's a big deal. It's overheating because you are working the engine and going no where.

I added some water wetter to my system and I also played with my suspension a bit to make climbing the rocky hills easier.


My E has overheated since the day I got it. Seems if you are not going 30 miles an hour in the open, it overheats. This has been gone over countless times in this forum and I have tried everything that seemed to make sense and a few things that didn't. This sunday in the tight stuff,,, no hills,,, it boiled over again big time. So I'm gonna try the ultimate solution. I am taking the complete cooling system off my "S", which is QUITE different,,, larger outlets, bigger hoses, different routing of the hoses and of course a fan. My "S" never boiled over once all summer and we were into some very tight stuff. I am going to put the fan on a switch and leave it run constantly when we approach the tight stuff and see what happens. If this doesn't cure the problem, this bike is out of here. I've had enough of this crap even though I love the bike in every other respect. My son on his YZ does the same stuff I do and he never overheats. I won't go to a 2 stroke,,, have been spoiled too much by the button.

Good point on the water wetter, it helped. I used that and the moose juice, after a nasty spill that chopped up a water pump hose. Also bought that DSP carbon fiber cover for the water pump. Still looking for some one with dyno numbers on their bikes, stock or big bore.

PJG55 you hottest day in PA is nothing compared to a summer sand wash in Arizona. The boil over you are describing is not normal. Most of my friends have gone to the DRZ400E and some boil over more than others but not anything more than the Wr,YZ,KTM,XR650 riders. The Kawasaki guys seem to have the worse problems especially the KDX200.

You are either not moving the coolant or have a leak. The extra cooling from the s model may mask the problem but it sure won't be solving it. It is a huge waste of time to mask a problem unless that is the system you plan to keep.

Victor,Victor, Victor,

It's not like my bike is the only one that overheats. My buddy's does the same and judging by the posts it is not an uncommon problem. Have you looked at the "S" cooling system? BIG difference and there must be a reason. Next time you are in Western Pennsylvania, stop by with Your Z, And I'll bet I can get it to boil in 10 minutes,,, summer or winter.


I tye wraped one small computer style cooling fan from Radio Shack to each radiator and hooked them to a on off switch on the handle bar. I just turn them on when ever the going gets real slow and have had no heatting problems sence.

ervin what size fans did you use

Hi Guys, try running Engine Ice Coolant (non-diluted) and it works a treat.

ervin what size fans did you use

This is a 6 year old thread :lol:

Ervin has not logged on to TT since July last year :eek:

Neil. :applause::lol: :lol:

This is a 6 year old thread :lol:

Ervin has not logged on to TT since July last year :eek:

Neil. :applause::lol: :lol:

:lol: :lol:

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