Overheating Troubleshooter

4 posts in this topic

Overheating can happen at any time of the year but it happens most frequently during summer. A warm running issue any other time of year can turn it into an overheating condition during summer.

Here are some of the most common things for you or your mechanic to inspect. It's formatted in an easy to print checklist.

Mazda 626 Overheating Troubleshooter


[] Low coolant

[] Coolant mixture incorrect (dependent on climate zone)

[] Coolant leak/puncture

[] Coolant loss (often mysterious loss is a sign of a blown head gasket as coolant is burned in the combustion chamber and will show up as thick white smoke from the exhaust pipe, can cause overheating)

[] Coolant temperature sensor

[] Radiator debris (leaves, bags, etc..)

[] Radiator fins damaged or clogged (mud, gunk, etc.. air must pass through fins)

[] Radiator cap (broken valve, seal deterioration, blown pressure cap)

[] Thermostat (stuck open/closed or not opening at correct temp)

[] Cooling fan and/or Cooling fan relay (dead fans are the leading cause of overheats during summer)

[] Water passage clogged (hose deterioration)

[] Water pump (broken or corroded blades)

[] Radiator clog (usually due to corroded rust accumulation from improper coolant mix or lack of glycol)

[] Heater core clog (for some reason most gunk ends up there)

If you are unfamiliar with how coolant or the cooling system works; coolant IS water, water is coolant. Automotive engines are primarily water cooled systems. When talking about the water pump for example, it could also be called the coolant pump. You don't want to use only water (distilled or tap) for coolant as it will eventually corrode your internal parts such as the radiator or water pump. That's why they sell special mixes of glycol and water in auto stores. The glycol prevents the water from corroding parts. It also helps resist heat more than just water. Glycol is a necessary additive to your water cooling system. A normal ratio of glycol and water as your coolant is 50/50. You can buy coolant in stores premixed OR mix it yourself. Make sure you know what you are buying in the store. It is either premixed or concentrate. Thus water IS coolant and vice versa when talking about hardware parts such as the water pump. Also, far up north you might refer to it as anti-freeze more often than coolant.

Here are some fantastic videos that will help you to properly diagnose and fix that pesky overheating issue without throwing parts and more importantly money at the problem.

If these videos can't solve your overheating issue then it's possible that your engine is worn to the point where your cooling system can't keep up with the heat generated by mechanical friction. Friction is bad. A mechanic will be needed from that point to better diagnose the issue.

If you want to see an example of what happens when you continue to run your car while it's overheating here are some prime examples.

Can I use liquid sealants such as Stop Leak to fix a blown head gasket or radiator leak?


Here are the cooling system specs for the 93-97 FS and KL.


If you need more info on the 93-97 cooling system then please read Section E1 of the 1994 factory manual.

If this has helped you in any way please let us know. It's only through the cumulative knowledge of members, EricTheCarGuy, and the factory manual that this was created. Stay dirty.

If you have an overheating issue due to something not mentioned here please let me know so I can update the list.

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I realize this is an older post but one of your coolant loss statements is mis-information I'm afraid.

[] Coolant loss (often mysterious loss is a sign of a blown head gasket as coolant is burned in the combustion chamber and will show up as thick white smoke from the exhaust pipe, can cause overheating)

Mysterious loss can be a number of things including heater core and the hoses as you mentioned. It also could be from a radiator leak (hairline crack where the plastic end caps meet the metal structure).

HOWEVER...I have never seen coolant being burned in the combustion chamber come out as BLUE smoke from the exhaust pipe.

There are generally 3 different colors of smoke that can come out of your exhaust. Black, white and blue.

Black smoke:

Black smoke is typically displayed when raw/unburnt fuel is not being burned in the combustion chamber, but instead in the exhaust system (typically in the catalytic converter(s)). Usually referred to as running rich.

Blue smoke:

Blue smoke is the result of oil entering the combustion chamber and/or exhaust system and burning. Most common culprit could be spark plug tubes are leaking oil into the cylinder, valve guides/seals or piston rings are worn.

White smoke:

White smoke is typically water vapor (steam). White smoke indicates blown head gasket or coolant is somehow entering the combustion chamber and vaporizing. Ever wonder why on a cold morning cars are always blowing white smoke out of their exhaust? Think about a glass of ice water on a hot summer day. Notice how it starts to sweat? Same principle just reversed. The icewater is outside, and the hot summer day is the car warming up. As it warms up, the exhaust 'sweats' and vaporizes into the lil' cloud of white smoke from the tailpipe. Now if it's 115 degrees out and you're blowing white smoke out your exhaust..very high chance you're head gasket is blown and you're vaporizing coolant.

edited by djdevon3: so the quote doesn't appear incorrect either... thanks!

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You're absolutely right. Good job. Got my oil and coolant burning mixed up. Thanks. :)

A mysterious loss is generally not attributed to a leak since a leak can be detected no matter how small (hairline fracture) with dye. Mysterious loss cannot be detected visually which means it's probably getting burnt off during the combusition process. ;)

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OMG I love you. Im also on the Ericthecarguy forum! Great forum post.

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