if u check honda's website it says that the 400EX is a 397cc 4-valve single overhead cam air cooled 4 stroke engine.

 

yeah, i don't know what kind of manual you have, but i would highly recommend not buying that brand anymore. lol[img]i/expressions/face-icon-small-wink.gif[/img]

 

Do you think a larger reservoir and cooler would help? Or is it to do with the slope and the oil return?

 

Would seem that the aftermarket companies sell a bunch of those.

I have to think that any added capacity or additional cooling area should help any machine run cooler but how much cooler is the question.

There is more than one "kit" avail for adding a second oil cooler on the 400ex some are designed to deliver the oil to specific areas like the one FST has that brings the cooled oil directly to the cam and rockers giving the added benefit of lowering the oil temp where its needed most and limiting the wear and need for hard rockers etc.

I am currently working on a project to see what changes just adding a second stk cooler will give. Its not expected to offer any major advantage beyond the fact that you can pick them up cheap on ebay etc but if the smaller less expensive and easier to mount stk size cooler performs even close to the others at reducing overall oil temps then there may be an advantage etc. but for now its just a project.

 

Most of the ones we raced against had larger coolers and air fins to help in flat track, but the most common complaint I have heard about a 400 ex fading has been in the dunes, where steep grades at full load are applied. I was wondering if the pump pick up could get starved due to the grade angles involved.

And as regards water cooling versus oil cooling....well a lot has to do with the specific cooling arrangement.....many heavily modded competition YZF 426's/440's(liquid cooled) had cooling problems after 15 minutes of hard running, making them very difficult to restart. The aftermarket cooling kits I saw were part of the problem. The radiator was located in front of the oil cooler, and the oil reservoir sandwiched between the exhaust pipe and the back of the oil cooler. The hot air from the rad, was then blowing into the oil cooler, and the reservoir was being further heated as this hot hair flowed over it and the radiant heat of the pipe cooked the oil in the reservoir even further. The physical arrangement had a problem in that it created a heat sink in the reservoir, never allowing the oil to cool but returning btu's to the oil from the very devices used to remove the heat.

Any time you boost the motor output to the levels seen in GNC or similar competiton, dissipating the heat is going to be a big issue in a longer competiton. Using a rad can actually hurt the process as seen in the example above.... mostly just due to space limitations about where to fit everything.

 

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