Coolant leaks when hot ?
 

OK...the deal is, after running the car for about 1/2 an hour the motor gets pretty hot. The other day when I got home I parked the car and noticed a bit of smoke coming out from under the hood. I immediatly opened the hood. No fire! I looked under the car and a small pool of antifreeze had collected under the motor on the passanger side. The smoke was from antifreeze leaking on to the pipes coming off the motor. In total I lost about a liter. The coolant only leaks out when the motor heats up. Any thoughts on what it might be? BTW the car is a 1987 420SEL with 99,991 miles on it.

It probably leaks only when the cooling system is pressurized from heating up. You may be able to find exactly where the leak is coming from by pressurizing the system with shop air (15-20 psi), if that's available to you.

Could you elaborate more on "the motor gets pretty hot".

(Only 9 more miles to the 100,000 club!)

the leak will need to be sourced and r/r'd:

>usual suspects: hoses, clamps, H20 pump, rad, overflow resovoir/hose, cap, heater core, etc.

most likely a good idea for a '87 car to have all the entire cooling system reviewed/ serviced/ maintained: hoses and clamps, thermostat, H20 pump, belts, etc. >>

hope this helps
-fad

An inexpensive way to pressure test at home is to rent a coolant system pressure tester from an Auto Zone or Checker/Kragen, if you have one near you. They have a FREE "loaner tool" program.

Just hook up the tester in lieu of the pressure cap on your coolant tank, pump it up, and wait for the leak to appear.

Have the front of the car up on ramps or stands so you can get a good look at the source from above and below. This is important because sometimes a leak on the underside of the engine can be coming from a hose or component above.

Apologies if this advice is too basic. Good place to start, though.

Thanks for the help guys. I gave in and took my auto to the car doctor. :rolleyes:

I had same problem. Turned out to be a defective radiator (expansion tank) cap. Mine was still the factory original.

I have the same problem but had the system pressure tested and the mech didnt finy any apparent leaks. Once I got home yesterday, I was short about 4 cups of coolant and the upper radiator hose had squeezed itself. I opened the expansion tank and the original shape was restored.

I believe pressure tests do not test the cap because the cap is probably removed while testing.

Suggest replacing the cap.

Steve,

That is a good tip about borrowing a pressure tester. I'd just like to add some advice on proper use. First and most important don't pump up the tester to more than about 15 lbs. If you pump it to the max you run the risk of creating a leak by blowing a hole in the heater core or something. Secondly,leaks usually don't occur when the engine is hot. The way it works is you shut off a hot engine when you park. As the engine cools the hoses,etc relax, and the residual pressure caused by the radiator cap causes about a cup of coolant to be forced out where ever the leak is. Once all the pressure is gone,the system tries to go into a slight vacuum, the leak stops. Each time the car is driven and allowed to cool the cycle repeats until you are way low on water.

Royaiii,
Your hose problem was due to a faulty rad cap. The radiator cap has several functions. It covers the hole so junk can't enter the cooling system.
it keeps the system under pressure in the range of 100 to 140 Kilapascals to increase the boiling point or our cars would overheat on a moderate day. As the system cools it refills the overflow reservoir under pressure and then tries to go into a vacuum. The radiator cap prevents this so you don't experience the problem you did.

Peter