I have an 08 Sonata that I bought from CarMax back in January and it currently has 32,000 miles. This vehicle is in very clean condition, drives nice, but has one problem - it is losing coolant - about half the reservoir is gone per week.

I can't find any leaks or puddles under the vehicle, no lights on the dash, the temperature is just below half where it should be.

I took it to the local Hyundai dealer and they couldn't find any leaks - they pressures tested it with a load of 20 psi for 30 minutes twice and the pressure stayed right at 20 psi. They said the next step is to add a dye to the coolant, run the engine and go over it with an ultraviolet light looking for a leak.

Has this happened to anyone else or has anyone heard of a service bulletin for this?

 

Are you refilling the reservoir? Or is it static at half full?

 

I refill it and it keeps going down at the same rate.

 

I am guessing that you are over filling the reservior and the excess coolant is being pushed out the top of the tank while you are driving around. On a cold engine, the coolant level in the tank doesn't need to be any higher than the lower fill line marked on the side. I would drive the car without refilling the tank and see if the level in the tank remains stable when you check while the engine is cold.

 

I don't see any evidence of coolant being pushed out the top of the tank. I didn't drive the vehicle at all this weekend and the coolant level in the reservoir went from the F level to the L level.

When I add coolant in the future I am going to add it up to L level and see if that slows down the rate of loss. I don't think this will change anything as two weeks ago I discovered the reservoir was completely empty.

I am definitely going to take this car back to the dealer to find the source of the leak, as this can't be a healthy thing. Glad it is still under warranty.

 

Was the engine at operating temp or cold when you noticed it was on the F mark? The coolant level in the tank will flucuate nearly this much between a hot and cold engine.

AH, you never said the tank had completely emptied out. Did you happen to check the coolant level in the radiator at the time. If the level was static where the hose bibb is attached, would suggest a crack in the tank or leak in the tank tubing. The total absence of puddles is what stymies.

Probably the best course of action. With no puddles forming under the car, especially if the car is just sitting, would suggest an interior leak on the heater core. Those give off such overt symptoms, I have my doubt about that as well.

Goog luck. Maybe someone else has some better ideas.

 

I am definitely going to take this car back to the dealer to find the source of the leak, as this can't be a healthy thing. Glad it is still under warranty.
Overheating is the number one cause of blown head gaskets and cracked heads and sooner or later it will over heat. It;s under warranty so I'd take it back and tell them you had exausted your resources to find out where the water is going and you are afraid to keep driving it. It is under warranty and their obligation to fix it, NOT YOU. LEAVE IT WITH THEM and tell them you expect it to be fixed in say a week. If they don't get it fixed then tell them you would like to swap it for another vehicle. Meantime let them furnish youa a car to drive and if they are a upstanding dealer ship they will cooperate with you.

Cracked head will make it lose water but when you start it up you will see white smoke (steam) coming out of the tail pipe and if you race the engine water will run out. What baffels me is it loses water standing still but no evidence of puddle underneath. Did you try putting cardboard under the engine overnight? Old worn out radiator cap gasket will make it lose water so invest in a new one.

Cooling system is one of the most important components of an engine but the most neglected and if it isn't doing it's job it can cause some mighty expensive repairs.

 

I finally decided two weeks ago to see what the owner's manual had to say about checking the coolant level. It says on page 6.9 "the level of the coolant should be between the "L" and "F" lines on the reservoir when the engine is warm with it at idle."

I had been checking the level until two weeks ago when the engine was cold and not running. The past two weeks it has been holding at a steady level.

From now on I will check it according to the owner's manual instruction - interesting that the Dealer never mentioned this way of checking the coolant level.