Has been done before on the 400ex, nothing special. I finally went ahead and did the oil cooler mod.

Total cost: $15.00, junkyard visit, oil cooler, transmission lines and zip ties.

Parts:

If I recall transmission oil cooler out of a Sebring.





Did not want to go with a very big cooler as to not affect oil pressure. Drove the atv like I stole it, and no more annoying loud ticking sound.



The front bumper plate protects the secondary cooler.













The temp gauge reading is the same as if pointing the gauge inside the tank by removing the dipstick.



Do get the typical 400ex ticking, although not as bad as before. Rode the trails today after a rainy Saturday. What a blast it was, could drive this thing all day and consistent power all the time. Engine stayed solid on back to back 1st to 5th gear launches, through water, mud, open dirt sections, all I can say pure fun.

Went from 8 to a NGK 9 plug, 93 octane fuel, ebay exhaust tip, and the Sebring transmission cooler. Maybe added about 3 ounces more of oil. The good thing about that cooler that it has metal bent lines from factory. In fact will go back and get the other side that has the double twist. As you notice one side is L and the other is like an S.

I do recommend this oil cooler mod, can ride the atv all day without any worries of over-heating issues in humid North Florida. As you can see the oil cooler its doing its job, temps are high in the cooler, and much lower in the oil tank.

 

With no cooling mods you can really feel the difference when it running hot. Riding in the winter is the best. I want to mod the cooling system. But not sure if I want a 2nd oil cooler or fan.
Your temps are low. What was the temp outside today?

 

83 most of the day and peeking no more than 85.

In regards to winter riding all I got to do is change to NGK8, and just flip down the main oil inlet and a oil line to connect to engine, then secure the secondary oil cooler for the winter. No more than a 15 minute deal.

I can definitely tell it is working, even at such temperature, mostly so at low end power.

 

I could be wrong but I dont see why you would have to unhook the second cooler for the winter.