The first sign is often the white smoke, sometimes you'll hear the fizzle or you'll even get a whiff of that all too familiar sweet smell.

You've got a leak in your radiator.

You certainly can't race and if you ride too long eventually the engine overheats and you'll face a load of problems. A number of reasons exist for a leaky dirt bike radiator but whatever the cause it's essential to stop riding and plug the hole.

Unfortunately though, it's not always as easy as simply plugging the hole. You'll need careful inspection of the radiator and hoses to find the leaky problem which generally occurs from the following:

  • Leaking hose
  • Swollen hose
  • Leaking coolant from water pump or water pump weep hole
  • Leaking coolant from radiator over flow
  • Leaking radiator

Ride long enough and you'll eventually encounter one or more of these radiator issues because you'll wear a part out, crash, bang bars with another rider or get sprayed with roost.

Leaking Radiator Hose

A leaky hose is the easiest and most convenient problem to fix. It's simply a matter of replacing the affected hose plus it's quite easy to pinpoint as the problem. A leak in a radiator hose usually occurs when damaged from a crash or by wearing out thus it either gets brittle or cracked through time or just can no longer hold the seal. But sometimes the hose clamp fails which is an easy and inexpensive fix.

If the radiator hose or clamp is the problem check out our Clamp Kit and Radiator Hose Kit for the solution.

Swollen Radiator Hose

You'll notice a swollen radiator hose right away (looks like snake digesting a big meal) and you'll need to shut off the bike to prevent the hose from popping off and spraying you with boiling hot coolant. A swollen hose results from a clog in the cooling system - somewhere - usually the radiator or a jammed water pump.

If the radiator is clogged you can try flushing it but most likely it needs replacing at this point. Using the wrong coolant or just not staying on top of maintenance is often the culprit in these cases. If it's the water pump you'll need to replace it.

On other occasions, a faulty radiator cap not releasing pressure when it's supposed to can cause a bulging hose or if your dirt bike is equipped with a thermostat, sometimes those get stuck closed creating a backup in pressure.

Regardless, a swollen radiator hose is a damaged radiator hose. Replace it.

Leaking Coolant from Water Pump or Weep Hole

Coolant leaking from the water pump weep hole drips under the water pump cover and you'll have to replace the water pump seal. Inspect the impeller shaft for any grooves otherwise expect the new seal to leak. Most water pump rebuild kits include the shaft as shown here:

Leaking Coolant from Radiator Overflow

A faulty radiator cap or using a cap with the wrong pressure release for your bike often contributes to coolant leaking from the radiator overflow. Buy a new cap.

But don't rule out overheating or a water pump head gasket leak that causes excessive chamber pressure. A head gasket leak allows combustion chamber pressure to bleed into the cooling circuit and vice versa. If the coolant contains oil and or fuel (coolant smells like exhaust or looks like milky oil), or the leak gets worse when revving the engine you're likely looking at a head gasket leak so grab a rebuild kit which includes the gasket. If the gasket leaks you might as well replace the related parts.

Leaking Coolant from the Radiator

The dreaded leak feared by car owners and dirt bike riders everywhere. If the radiator on your dirt bike leaks you've probably got a pretty big issue. Never mind the 5 cent repair jobs (like plopping an egg in) unless it's to get you back to camp therefore use quick aluminum. But it's not a cure, so get a new radiator.

Radiators often get damaged in crashes but also from roost kicked up by the guy you're chasing. Or in the case of extreme racing, getting hit in the side by a dirty rider. Once damaged, it's usually beyond repair and you're better off replacing rather than nickel and diming yourself to future breakdowns. Also, riding in heavy mud conditions clogs the radiator which results in overheating and potential damage to your engine or the radiator.

You can prevent much of these issues from occurring by adding some protection:

Once the radiator is damaged it's best to replace it so you don't encounter issues later. And yes, you can replace one side or the other as long as the other side is undamaged otherwise you'll have to replace the whole system.

A final note: Radiator fins break or bend quite easily preventing air from passing through or creating pin holes in the radiator veins. Use caution when bending the fins back into place and when cleaning your bike with a pressure washer.

Remember, whenever working on the radiator don't open the pressure cap until the bike cools down.

Written By: AndrewT