View Full Version : Cooling a snowmobile engine...

02-14-2013, 04:51 PM
So our sled powered go kart has been coming along really well and we are close to finishing, but I received some concerning news from someone who owns the same type of snowmobile we got our engine out of: a 1981 Kawasaki LTD 440. He told me that even in below freezing temperatures, that snowmobile engine will overheat while idling. And that's with a radiator and heat exchanger. This particular engine apparently runs very hot. We were planning to install the stock radiator onto our kart but got rid of the heat exchanger (since its cooled by snow kicked up by the tread). So now we have a bit of a dilemma... we can keep building, but it seems quite certain that our kart won't be driveable for too long with this setup. Our first thought is to just buy a bigger radiator, but we don't know anything about radiators, the different kinds, or what will give us enough additional cooling to take care of our problem. Any advice/information is greatly appreciated. Thank you!

(We also know that an electric fan will help at idle so we plan to get one of those regardless at this point.)

02-14-2013, 05:10 PM
An electric fan should take care of the problem at idle &, once you're moving, the rushing air being forced through the radiator should take over.

If you're super paranoid about it you could create some deflector panels to direct the air towards the radiator

02-14-2013, 05:25 PM
get a big radiator and electric fan. also get a temp guage so that if it does start to get too hot you can stop before its too late

02-14-2013, 05:45 PM
Thanks. We do have a temp gauge so at least we can monitor what is going on. Is there any hope in keeping the stock radiator, installing a fan for when it's idling, and then hope the air rushing through it will be enough to cool the motor when the kart is moving?

Doc Sprocket
02-14-2013, 05:58 PM
A temperature gauge is a very good plan. However- Do you know what the temperature should be, to compare to?

I would also find out what the factory thermostat opening temperature is, and maybe see if a cooler model is available.

02-14-2013, 07:06 PM
i agree with everyone that says "a bigger radiator and a good fan". i'm hoping that the aftermarket honda civic radiator i got for greaser's buggy will do the trick.

what radiator are you planning on using now? can we see some pics of it, and some pics of how you plan to mount it?

Kaptain Krunch
02-14-2013, 07:41 PM
Every liquid cooled sled will overheat idling. Get yourself a very small car radiator, or run 2 smaller rads, also an electric fan with a thermal switch. should have no issues.

02-14-2013, 07:47 PM
You'll be perfectly fine with a larger radiator and fan.

02-14-2013, 10:53 PM
Sounds great. Any suggestions on what model car to look for radiators for? I looked up some Civic radiators on ebay and the prices are not bad and some come with a 12" fan. Only problem is they are still a bit big... we want to have it angled right next to the seat and I think the Civic one would stick out past the rear wheel. Something around 12" wide would be ideal.

Also... how about a motorcycle radiator? Something from a high revving sport bike?

02-15-2013, 02:46 AM
the biggest you can fit. bigger equals cooler. more surface area to radiate/exchange heat. maybe think about mounting it ever so slightly behind you so that can use a bigger one and it can still get good air flow. with a fan behind it sucking air, that should do the trick. you wouldn't want the fan in front, that's just hazardous - especially if anyone with long hair want to ride it. lol.

02-15-2013, 03:10 AM
The civic rads are about the best u will get
The most common, easiest to replace
Unless u go to a car wreckers and just start rifeling though their collection

Also it's not all about size

Radiators come in a range of thicknesses
The civic rads come in 2,3 or 4 core

Again it's about surface area

As for the fan

It has to be behind the rad
It won't work nerely as well if its in front
It'll just cavitate

It is also best to have the rad as far back as u can
If a hose were to blow then u don't want hot coolant running down your back

U can mount the radiator so it slots behind the engine a bit
That'll still cool it quite well

If the OEM didn't have a thermo switch installed then u are going to require one to control the fan behind the rad

If end up going to a wreckers then get a rad with a transmission cooler on the bottom
Then u can run an oil cooler
An oil cooler will make a world of differance over a fan in front of the engine
Or u can run a separate oil cooler

02-15-2013, 08:23 AM
Might be a good idea to go look through a junk yard and see what they have, if anything to get an idea of what would work best for your setup.

02-15-2013, 09:27 AM
Thanks! So something like this should work?


I also just realized that the rad hoses on a car are bigger than those on this snowmobile... I'm guessing there are hoses that have different size inlet/outlet?

Also - Would we need a thermal switch, or could we just hook the fan up to a regular switch and manually turn it on when the kart is idling and turn it off when it's moving?

02-15-2013, 10:52 AM
I also just realized that the rad hoses on a car are bigger than those on this snowmobile... I'm guessing there are hoses that have different size inlet/outlet?

You can try to find different hoses or change the inlet & outlet sizes on the radiator. You'll have to find someone to weld aluminum, if you can't.

How about a Kawasaki 500 radiator and fan? If it cools a 500, should be good for the 440.

Check this one, too.

02-15-2013, 11:22 AM
The EX500 radiator is a great suggestion... but I don't see a radiator cap on it :huh:

I guess that bike has a coolant reservoir where you add coolant?

02-15-2013, 11:52 AM
I can't believe nobody has mentioned water misting. Super easy to do. Plus keeps temps really cool. All of us import tuners run it for our intake temps. Simply set the mister toward the block and head. When idle give it liberal spray and the heat from the motor will evaporate the water and dissipate the heat from the motor. Easy, cheap, reliable. Not often you get all of those.

02-15-2013, 01:14 PM
You can try to find different hoses or change the inlet & outlet sizes on the radiator. You'll have to find someone to weld aluminum, if you can't.

How about a Kawasaki 500 radiator and fan? If it cools a 500, should be good for the 440.

Check this one, too.

The one problem is that that's a 500 4stroke and this is a 440 two stroke possibly putting out over double what that 500 was so there's a good bit more heat to dissipate.

Oh, and snow kart for a older lc sled engine anywhere from 140-180F is the normal operating temperature.

02-15-2013, 11:00 PM
Thanks guys. How about two 2 row radiators like this? I guess I'd have to get a fan for at least one of them separately....


02-15-2013, 11:23 PM
i'd go bigger, your engine is almost twice the size

02-15-2013, 11:50 PM
A motorbike radiator just won't cut it

It may work in the short term but u will notice after a while the engine just won't go as hard as it use to and it will over heat more often

U can get civic rads with smaller fittings

u can put a reducer in your lines if u are using a wreckers rad

02-16-2013, 08:35 AM
Where can I find a civic radiator with smaller fittings? That's our biggest concern with that one. If we can't what does a reducer look like for radiator hoses? Thanks...

02-16-2013, 09:38 AM
A reducer is just two bits of pipe welded together
Each of its own size

U would have to search though eBay to find a reduced outlet rad

Search EG EK manual radiator

02-17-2013, 06:37 AM
Sorry if I'm writing the same as someone else. Didn't read the whole thread. Honda civic radiator with an electric fan. No chance the stock radiator will keep it cool. Lots if guys use civic radiator in buggy swaps and the work great. You shouldn't have any issues with that setup. Alright just read through it. Fowlers pointing you in the right direction. I run the fan through a switch on my buggy. Once its warmed up I turn the fan on and leave it on even a few minutes after I shut it off. No need to turn it off while moving. Save you $40 on a thermo switch. Don't worry about an oil cooler though. That 2 stroke doesn't have oil to cool. No offense to the tuner guy but don't spray cool water on the engine. Bad idea especially on the exhaust. A civic radiator is the hot ticket for sled engines during summer time.

02-17-2013, 01:38 PM
Awesome, thanks. The consensus certainly seems to be that a 2 row civic radiator with a 12" fan would be ideal. They are inexpensive and I'm sure would get the job done based on what I'm reading. The one issue with a civic radiator is it's size. They are roughly 14.25"L x 17"H x 2"W and that would be hard to fit onto our kart without it looking a bit ridiculous (see model below for an idea). So, after doing some more research, I came across mini cooper radiators that are being sold on ebay. They are aluminum, 2 row radiators, same as the civic ones, but are smaller (about 10.5"L x 14"H x 2"W). This would fit and look a lot better, but of course the downside is less surface area. The last thing we want is to get a radiator and have it not be enough to cool the motor and have to buy another one...

I want to see if I'm thinking about this correctly, so here are some specs of the original vs. civic vs. cooper radiators:

Original Kawasaki Rad
Core size: 10.5" x 6" x 2" (I believe it's 2 row, just based on measuring the width at 2"... see pictures)
Surface area: 126 in.sq.
Fan: None
Additional cooling: snow cooled heat exchanger

2 Row Civic Rad
Core size: 14.25" x 13.75" x 1.50"
Surface area: 294 in.sq.
Fan: 12" puller

2 Row Mini Cooper Rad
Core size: 10.375""x 10.25"x 1.75"
Surface area: 186 in.sq.
Fan: 10" puller

Does this mean the cooper radiator will be only slightly better than the stock unit and the civic radiator's cooling capacity will be over double the stock unit?

Below is a 3D model of what the cooper radiator (left) would look like vs. the civic radiator (right).

Should we even consider the cooper radiator with a 10" fan based on this? Assuming these are all made of aluminum, are the surface area or the radiator and the # or rows the only significant factors to consider? Thank you!

Doc Sprocket
02-17-2013, 01:56 PM
Since I know nothing about the sled- There's no fan? Well no wonder it'll overheat at idle. Has anybody considered the notion that an electric fan shrouded to the stock rad would grossly outperform the non-fanned original?

That said, you could get away with the Mini rad, I'm sure. Be sure to use a shroud to maximise thermal transfer efficiency. The factory Mini shroud combined with a factory fan and rad are a no-brainer match.

If you were not planning on running a fan, then you need a big@ss rad. If it were up to me, I'd use a smaller rad and fan.

EDIT- Another thought- Have you considered dual rads? A couple of bike rads (with fans), one on each side. If they can keep a high-performance bike engine comfy in a summer traffic jam, I can't imagine why they couldn't keep a sled engine cool.

02-17-2013, 02:11 PM
That's a good point. The snowmobile did not have a fan for the radiator... however it did have a heat exchanger at the rear of the tunnel which was cooled by snow being kicked up by the tread. So the coolant ran from the water pump, to the radiator, then to the snow cooled heat exchanger, and then back to the motor. It certainly makes sense that the engine overheats at idle since there is no air moving through the rad and no snow being kicked up onto the heat exchanger.

However, my buddy who owns the same model Kawi snowmobile that we got our engine out of said that this engine generates a lot of heat, and even when the snowmobile is at speed, but there is no loose snow to throw onto the heat exchanger, it will run hot. Since we obviously won't have the heat exchanger, I feel that based on his experience, the stock radiator would definitely not be enough, even with a fan. Again, we just don't want to buy the Cooper rad and have it not be enough. That's why I'm trying to do the math to see if I can get some certainty that the Cooper radiator will be enough before purchasing it.

Doc Sprocket
02-17-2013, 02:24 PM
I understand what you're saying, but I counter with this:

The stock sled rad (without fan) relies on air being forced through it at speed. I would imagine that the rad is NOT out in the open, but behind some bodywork- with vent openings, I'm sure. Now- Can you imagine the heat transfer efficiency if you were to duct a high-performance fan to it? I guarantee it would stay cool. Armed with that concept, I would bet a paycheck that the Mini rad, shroud, and fan will do the job just fine.

02-17-2013, 03:13 PM
That 2 stroke doesn't have oil to cool.

Ha forgot we are working with two strokes
Yeah that wouldn't work too well

U proberbly could use a copper rad
But then cost comes into it

If its cheap enough to go that option then u can

Dual rads may work if u are keen to have double the lines running

But bike rads are usually long, skint and curved
They dot really fit in a situation when u want the rad as high as possible in a wide area

Doc Sprocket
02-17-2013, 03:34 PM
Depends on the bike. I have an '83 Interceptor that uses 2 small, square rads.

02-17-2013, 03:55 PM
Ha forgot we are working with two strokes
Yeah that wouldn't work too well

That doesn't sound encouraging lol. An aluminum 2 row radiator won't cut it? I was just thinking that the mini cooper radiator is made for a car with a low revving four stroke that puts out no more than 50hp probably. I need to cool a 70hp two stroke so not sure if that would be enough. Do you guys think the civic radiator won't cut it either? Thanks for all the help.

Doc Sprocket
02-17-2013, 04:06 PM
Fowler was referring to the use of an oil cooler. Not feasible on a two-stroke.

02-18-2013, 11:48 AM
Ahh ok. What do you think about the fact that the cooper radiator is designed to cool a small four stroke putting out no more than 50-60hp while I'm trying to cool a 70+hp two stroke which revs to 8k rpm? I was about to click buy on a cooper radiator on ebay but then thought about this... what are your guys' thoughts? Again, we just don't want to spend north of $100 on a radiator/fan and then have it not be enough. Thanks

Doc Sprocket
02-18-2013, 03:08 PM
Personally, I believe it will suffice. Stick tight for other opinions.

02-18-2013, 06:47 PM
A mini rad would be ok

02-18-2013, 08:55 PM
One more time- http://mistercycle.net/get-your-mister-cycle/mister-cycle-for-street-bikesfull-dressers/
Used it on my two stroke bike.

Ted Hamilton
02-18-2013, 09:05 PM
Be aware that moving air too quickly through a rad will not give it time to heat up and remove heat energy from the coolant.... a thicker core rad with slower airflow may be better....ducting on the face would be a good idea.... Good luck!

02-18-2013, 10:13 PM
A mister isn't a good idea

A mister is a short term thing to get out of an emergency

I agree with ted
A good thick rad is good
And volume over speed

02-19-2013, 08:41 AM
Thank you all very much for the input. After reading everyone's suggestions, I think we'll be getting a 50mm Mini Cooper radiator...


...they are a bit more pricey than the 40mm ones but will offer better cooling and slower airflow. This, paired with a 10" fan, should hopefully do the trick. I don't know how effective misting would be, but I'm not sure I like the idea of spraying the spark plugs and exhaust with water. Also, it seems to be fairly costly anyway.