Losing radiator water

My 1995 Chrysler LHS loses water. It boils out from the fill cap. The car will eventually overheat once the water level gets to a certain low point if I do not replace the lost water. The car seems to otherwise run okay. What’s my problem here?

Didn’t radiator caps on old cars have to be periodically replaced because they were fitted with thermostats? Is this the case with my car even though my fill cap is not actually on the radiator?


If you are losing coolant past the radiator cap at normal temperatures (no overheating) replace the cap.

I assume you are talking about the radiator cap and not the cap on the reservoir. The radiator cap has a spring that holds pressure up to a certain point, and then releases. If this spring is weak, the coolant will boil out around the cap. There is also a rubber gasket to seal the cap against the fill neck of the radiator. These caps are inexpensive (under $10) and can easily be replaced.

If you are losing the coolant out of the reservoir, again start by replacing the radiator cap on the radiator. If this still happens, your cooling system may be pressured by a faulty head gasket. However, I’ll bet on the radiator cap.

I didn’t know that my car (95 Chrysler LHS) had a radiator cap. The water boils out of the system from the reservoir cap. Where is this radiator cap located?

I don’t think your car actually has a “radiator cap” per se. (and FYI, I don’t think you have a drain plug for it either) My job’s work van is the same way.

If you’re not replacing the lost water fast enough, I guess it’s possible that some air is getting into the system- then you add water on top of that and drive it around till it gets hot, the resulting pressure diff may cause it to boil over like that… just an idea.

What you are looking for is the pressure cap, whether it is located on the radiator or on an expansion tank (not the same as an overflow tank). I don’t know where it is on your car.

You might also have a head gasket failure.

If you are actually using straight water in your radiator, rather than the required 50/50 mix of antifreeze and water, then your engine could be chronically running hot, and the water could actually be boiling away due to the high temperatures. Please clarify exactly what you have been putting into the cooling system!

I have been topping up with regular water but periodically putting in another gal. of antifreeze. I guess that I could flush and re-fill the system with a clean 50/50 mix. I’ll first replace the pressure cap at the fill tank.

How can a head gasket failure be diagnosed? If this is the problem, roughly how much $ is involved in replacing it? This is a job that I’m guessing I would not be competent to do. The last cars I owned that I enjoyed working on were my 55 Chevy Camio, 62 Chevy SuperSport (327), 64 Triumph TR-4 and my 64 Corvair 500. New cars? No way.