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1999 Seville STS coolant leak


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Hi!

My 99 Seville STS is leaking some coolant everytime I drive it at higher speeds, such as 90-100 mph or above.

It is coming from the drivers side, there is coolant on the air deflector (the plastic cover underneath the radiator).

The radiator is new and the upper and lower radiator hoses are in good condition. It isn't coming from the expansion tank, everything is clean and dry if you open the hood and look down.+

(Head gaskets are new as well!)

Any suggestions?

Thank you!

Chris

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The best way to handle this is to pressurize your cooling system. You can either purchase a cooling system pressurizer or go to a radiator shop that has the equipment to do so.

My guess is that your water pump body seal is leaking, or your crossover seals are leaking, but it will become obvious under pressure

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

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The cooling system has already been pressure tested, but there are no obvious leaks. At about 20psi the upper radiator hose was leaking, that has been fixed (but thats on the passenger side).

Water pump and thermostat including seals have been changed when the head gaskets have been replaced and I couldn't see a leak from above.

It looks like the coolant is leaking somewhere from the very bottom of the car because there are no signs of leaking coolant visible if you look at it from above.

Where are the "crossover seals"? I have some problems with english technical terms.. never needed it before (I'm from Austria...)

Thank you very much!

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I had it pressure tested just 1 hour ago... he told me that my radiator is leaking and that the clamps don't look fastened enough.

The radiator is from "proliance" and just 2 weeks old.. is that a defect from the producer or something that the mechanic did wrong?

I think thats strange, because of the same failure (radiator leaking at the driver side) I had the old one replaced, and the new one seems to have the same problem?!

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If you have taken the system up to 20 psi and found no leaks that is good

Keep in mind that at 100 mph the water pump is turning quite fast, and that turning could be rocking the water pump, allowing pressure to leak, while a static pressure test would not reveal a leak. Make sure the water pump is seated fully

The crossover, is what the water pump is attached to. The crossover is attached to each head at two locations on each head. There are 4 seals. Do you know if those seals were replaced during the head gasket repair?

Are you sure the radiator is good?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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start with the simple stuff. hose leaking? replace clamp. replace hose. still leaks? change radiator. check with shop and verify replacement warranty so there is no issue about inlet/outlet deformities. who pays for labor for changing warranty parts? the system pressure at 70mph versus 100mph is minimal. the thermostat stays open longer to regulate temp. i would not expect a caddy to have cooling issues at 100mph.

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Cooling works good, no problem with overheating since the head gaskets have been replaced!

Coolant leaks only when i drive pretty fast.. not very much but enough to have a small puddle under the car

I will ask the shop that did the head gaskets if they have replaced the 4 crossover seals, but I think so!

When we put 18psi into the cooling system it was only dripping a little bit, at a litte more psi is flow out from the bottom of the radiator (the lower hose doesn't leak, could see it from underneath the car) It's flowing down the radiator, but the leak is not visible :(

Maybe the problem is like you said... 20psi is too much for the system so it starts to leak, the pressure cap will only hold 18psi while driving and there is no leaking at the pressure cap, so I think that i didn't reach 18psi on the highway (no speed limit, for a short distance the speed went up to 120-125mph)

So I will also have the waterpump checked... Would be very strange if the old and new radiator leaks on exactly the same place! I couldn't find anything about the quality of the Proliance radiator, but it looked good! A new one from the dealer in Austria (AC delco) would cost about 1200 US Dollar, so I bought the Proliance part at Rockauto.

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I have used the Proliance radiator, its an adequate part.

If it does not leak with static pressure, vibration must be causing a leak at 100 mph, think on that idea. As Joe said, check clamps, etc

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Should I use tablets for the cooling system? Could that help? The only problem is, that the Cadillac dealer over here doesn't offer such tablets :(

I only got the light-red cooling fluid mixed with 50% water.

Once you find the leak, you can use the cooling supplement, not before it might disguise the leak

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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