dissapearing coolant diagnosis

[Ray_73Turkis_OH]

Here are the clues.

Driving lots of shorter trips around town (say about 500 miles total) and the coolant in the radiator goes down, about an inch.

Top it up, drive to Chicago and back (650 miles) last week and there is no change in the level in the radiator.

No coolant visible in oil.

I have checked all possible external leakage points and don't see anything.

My theory is a head gasket water leak that goes away when the thing is hot, therefore, no leakage on a long trip.

Any other theories.

[DanOKC]

Your probably right, another possiblity is small crack in the head that seals up after it gets hot, which short trips might not do.

[Beaner7102]

How old is your rad cap?

An old cap will release water at lower temps as the spring looses its tension over the years.

In lots of stop/start driving in heavy traffic your temp will be higher than crusing on the highway.

Also the water should be about 1" from the top anyway to allow for expansion, 1/2 a gallon down would be a worry.

Just a thought. Beaner7102

[c.d.iesel]

.......and/or your just over filling it and it pushes the excess overboard

when it's full hot - the level should be atleast 2"below the cap

fitting - see the BUMP inside the radiator for cold fill mark

that's why they call the top of the radiator the 'expansion' tank

section

and/or your ignition timing is Way Off, thermostat wacky,

radiator core plugged, fan blades missing, water pump

housing corroded away and large clearance between

the water pump impellor and housing - loosing flow

volume

and/or your head/gasket are leaking/cracked......

early stages

and/or wrong Non-BMW radiator cap

or leaking coolent /heater hoses OR heater core

or leaking water pump

[tbrduc]

Lots of good tips in here, for sure.

Thanks C.D.

[peteinjp]

Well the car runs hotter in stop and go traffic so its more likely to spew around town. First thing I'd check is the radiator cap- correct cap in new to very good condition. I also vote for possible overfilling. My car does this too if I fill it to the base of the rad neck. If it were a head gasket or any other kind of leak etc then the coolant level would get lower and lower. If yours finds a spot and stays full to that spot then it seems unlikely to be anything that would leak regardless of coolant level. Where does the needle sit on the temp meter both highway and around town? How is the general condition of the cooling system to your knowledge?

[stone02]

Hi,

well i have seen this in many customers

cars with the exact same symptoms. i have

found that in many cases the heater valve is

the culprit. when you operate the car in short

cycles the engine builds and disipates heat and

pressure. the car starts out with 0 psi in the radiator

and builds up to the release pressure of the cap.

then the cap releases the coolant. most caps

hold 15 psi which allows the engine temp to rise

up to 235F approximately. well the heat and pressure

find those little o-rings in the heater valve and push

coolant past them. the coolant doesn't flow past

the o-ring it is nearly vaporize and cant be seen.

you may see a small indication on the top of the

heater box that looks like calcium deposit.

so you can do a few things. change the heater valve,

loosen the cap, or BEST replace the cap with a low

psi release like 7-9 psi this will protect the o-rings

and the old radiator from blow-outs.

good luck

post the results

stone

[Guest Anonymous]

My car does the same thing. If I fill radiator to filler neck and drive normally upon recheck the water level is about 1" below where I filled it. I think it just boils out the release pipe. Temperature remains constant at the 4:00 position on the meter.