Tech Tips: Replacing Radiators and Coolant

Damaging a radiator can be a common occurrence when your bike goes end-over-end, or just tips over in a corner. Swapping out one can be a messy situation, so check out our latest Tech Tips on how to change out your radiator and also replace the coolant.

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Transcribed version:

"Hey, this is Michael Lindsay from Vital MX. We're here at Chaparral Motorsports today, and I'm sure as many of us have done, we've either crashed and damaged, or broken the radiator, so we're gonna show you how to replace it along with changing the coolant. Now that we're here in the shop with our RMZ-250, we're gonna start by draining the coolant before we get into getting the radiator off. Tools-wise, this is a pretty simple process. Mostly just need like an eight-millimeter T-handle to get the plastic, the radiator off, the drain bolt, a Philips screw driver for the radiator hose clamps, maybe an Allen key for the drain bolt, but for the most part should it be an eight-millimeter. 

So, one of the first things you wanna do is make sure you have the bike as far over on the stand as possible to expose its drain bolt so the fluid can flow out without draining onto the stand or anything being in the way. A lot of the's also really good to take the engine case guard here out of the way as well, so you either don't get coolant in it and it's also out of the way of your drain pan. Now before we take the drain bolt off, we're actually going to want to loosen the radiator cap and take it off. This is so air can enter the radiator as the fluid is escaping. For the most part, the coolant and drainage is usually on the water pump cover. If you look at your cover, you'll usually find most of the bolts go through all the way to the case, so look at your bottom bolt. Typically, the bolt above it is actually the coolant drain. Easiest way to tell is look for a copper wash on the back of the bolt, which tells you that it is sealing a type of fluid. 

Now just to ensure that we've actually drained as much of the coolant out of the system as possible, we're gonna try to hold this here, and lean the bike over. And in this case, it might be a good idea to have two people help you, just so you don't end up under the bike. But if possible it's usually pretty easy to just grab the handle bar and lean it over on the stand a bit, just get a little extra out of there. Now that we've drained the coolant, we're gonna go ahead and get the radiator shroud off, so that we can get down in here and work on the radiator and get all the hoses off without anything getting in our way. You know, usually a radiator shroud is more than likely three to four bolts, typically an 8 millimeter, so of course this is pretty easy stuff. Just take a look at the radiator. Find where the radiator hoses mount to the radiator and start from there. Go ahead and take your hose clamps and loosen them. And go ahead and remove the radiator hose. Biggest thing you wanna do is to remember if you have a hose that's stuck, don't grab a set of pliers and try to compress the hose and pull it off, unless you're gonna do it way back here, because there's a high chance you might do it too far up on the hose and crimp the inlet or outlet hole of the radiator by accident.

The majority of our radiators are usually mounted in two places, in front of the radiator to the frame. Usually, the radiator louver is almost always in the way. On some brands, you may have to undo another bolt to get to these. Sometimes they just pop right out of the way to allow you access to the two bolts. And as you can see, I've made a little bit of a mess here, because we did have a little bit of coolant here in the bottom. So, if you have a bike that has a radiator mounted on each side, as the majority of our full size models do, there's a little cross-over tube here that connects the two radiators, you're gonna wanna undo. Sometimes I like to wait to do these last, so I can take the radiator here and try to twist it off. This one can be a pain, and usually if we're dealing with the right side one, we also have the overflow tube here. You can either choose to remove it or pull it up through the entire bike. Depending on the hose, sometimes I've had better luck just taking the hose out instead of tearing it trying to get it off, as these hoses usually aren't that tough. 

Just make sure you check the routing of where this hose comes from so you can put it back where it belongs later. Now we have our radiator off, as you can see, it's pretty straight forward. The radiator we're using, albeit a little bit dirty, is actually fine. We have no damage, so we're gonna remount this. If you didn't have a radiator that was damaged, and you're actually putting a new one on, usually you're gonna have to take these spacers and lower-upper grommets out of your old radiator and place them in your new one. Usually you'll press these little guys out, and then just push the rubber grommet out and push them in the new ones, put these back in, and then you can put your radiator back on, or your new one on. Based on my personal preference, I usually take this overflow tube out so, you know, kind of route that down, the direction it needs to go before I get started here. Now that we're back in here we're gonna put the cross-over tube on first. You can usually just grab that with a set of needle nose, and work it back on. So in this case since I'm able to wiggle around the radiator because it's not bolted down yet, I'm gonna go ahead and put my radiator hoses back on. Now I'm gonna clamp the radiator back down. Of course, I wanna remember to clamp down our radiator hose clamps. 

Big thing is, once again remembering, when you get the hose on, you can feel along the hose where it's soft. Here is the lip of the inlet tube. You wanna make sure that the hose is on far enough, that you're getting the clamp up and above that little ridge, because the clamp sucks down around the hose behind that ridge, and that's what helps hold this on. So you wanna make sure you're not clamping the radiator hose clamp around that edge, or otherwise more than likely you're gonna have a radiator hose that won't be sealed properly and may slip off during use. For the most part, you don't wanna make these too tight. Big thing to watch for is in the middle of the radiator hose there are these little cleats. Usually, you're over-tightening it if you're starting to see the radiator hose actually protrude through the radiator hose clamp. Now that we have our radiator hoses tightened back up. We're ready to fill the bike with coolant. In this case, we're gonna use the same kind of coolant we were using before. But if you're switching coolants, mostly if you're going from a water based to a non-water based coolant, you're gonna wanna actually flush the system. And in this case that means you don't wanna flush it with water. You're actually gonna wanna use compressed air to get it out. 

A good idea is to take like a rubber tip air nozzle that you can seal, top of the radiator. You're gonna wanna take the hoses off, blow air through the system, get all the coolant out. Take your other side, do the same. Big thing, is basically, look at the cooling system because it's different from bike to bike. Find where coolant is whether if it's in the engine. You're gonna wanna take the radiator hose off the top, and take whatever the exit system one is out, blow air through there, so it gets out of the cylinder water jackets, and gets clear of the engine. You're gonna wanna do it to both radiators, all the hoses, just every little area of the cooling system to ensure that you've gotten the entire system cleared before you start filling the bike again. So now we're ready to fill our bike with some coolant. Big thing here is, now we've gotta get all the air out of the system. For the most part on motocross bikes, this is not very difficult. First thing we're gonna do here is fill our radiator until it appears to be full. Because we do have the cross-over tube, we have access to the other side, so the easiest thing to do is lean the bike towards the other radiator, allowing fluid to wash over into the other side and allowing...

For the most part, you can usually get the air to come out of the other radiator going uphill, and it'll escape out this side. To know if you're successful, basically you'll set the bike back down, and as we had happened, our coolant level has actually dropped because it's gone into the other radiator. And it's allowed more air to escape. If you do end up with a bike that does not have a bleed on the opposite side of radiator, and you wanna ensure all the air is out of the system, you can do with a bike as you would with an automobile. You can start the engine with the cap off. This will allow coolant to go through the engine and through the entire cooling system. It'll bring air up to the top and allow it to escape through the open radiator cap. 

Of course, because of the heat build, you don't wanna have the bike running for more than maybe a minute or so, just to ensure none of the fluid starts to push out of the bike. From there, things are pretty straight forward. You're gonna re-install the radiator cap, the radiator shroud, louver, engine guard, put all your bolts back in, tighten everything down. From there, you've either replaced your radiator, you've freshened your coolant, your bike is running cool, and is ready to go. If you wanna check out more tech tips, jump back to for more."

Credit: Joe Carlino
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