1996 STS coolant overflow
 

I own a 1996 Seville STS. By design, there is no coolant overflow tank and occasionally the coolant reservoir, which is mounted on the passenger inner fender,will leak coolant out of the radiator cap. I have replaced the cap with a new one, but still see the coolant leaks, when the reservoir tank is full. Is this normal? This is the first car I have owned without an overflow tank. So I am under the impression the reservoir tank should always be full...conversely it is always low. The car does not run hot according to the temp gauge. So, I see no evidence of the thermostat sticking, or causing overheating. Everything seems to run normal...just the annoying coolant leaks through the cap and the resulting low coolant level. I am wondering if this is par for this model. Anyadvice would be appreciated.

RE: 1996 STS coolant overflow
 

i dont think so.
something is amiss.

RE: 1996 STS coolant overflow
 

I believe that what you are referring to as a coolant reservoir tank is what I call the coolant
expansion tank. As the engine heats up the coolant expands and needs a place to go.
How full are you filling the expansion tank? When the engine is cold it should only be about
1/4 full. As the coolant temp. rises the coolant will ' expand ' into the tank. If you keep
filling the expansion tank to the top, the heated coolant has no place to go but out through
the overflow hose. When the engine cools, it creates a vacuum in the cooling system that draws the coolant back into the radiator. Do you keep adding coolant to the expansion tank
to keep it full? If so, you are probably overfilling the cooling system and when the coolant gets hot it just keeps spewing out.

RE: 1996 STS coolant overflow
 

To clarify, GM doesnt make cars that dump coolant at the end of the day.

RE: 1996 STS coolant overflow
 

Thanks for your excellent clarification of what I was trying toexplain earlier in my post. Yes, you are correct in the fact that I was trying to keep the expansion tank full, rather than 1/4 full. I should back up and say that I have two Cadillacs, one being a 1992 Deville, with an "overflow tank". So, I am familiar with keeping the radiator full and not worrying about the overflow that is captured in the overflow tank on the 92 Deville. On the 92, if the radiator is a little low, as the engine cools down,the vacuum created in the radiator would draw coolant from the overflow tank into the radiator via the checkvalve on the radiator cap. What concerned me with the 96 Seville is that there is not anoverflow tank to catch the spillage, and/or draw additional coolant from when the system needs extra coolant. The radiator cap is the same for both--same checkvalve feature--but the Seville has no coolant reserve to draw from. I figured any fluid lost wouldcreate an air bubble which could harm the Northstar engine. I was just surprised to find the Seville designed without an overflow tank, like the 92 Deville had. Having clarified all that, I have always owned GM...good product and very pleased over the last 40 years. Thanks again jerrymac for your excellent response.

RE: 1996 STS coolant overflow
 

i am new to caddilacs and forums so how do i post a forum asking for help with my caddy problems???? this right here is all i can do...