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1999 Deville
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35 Posts
Discussion Starter #1
Lately I have been noticing coolant loss in my 99 DeVille. It's sort of baffling me because I don't see a steady coolant drip or puddles on the ground. I am not seeing overheating as long as the coolant recovery tank is full but some how I am losing coolant. I thought maybe the coolant recovery bypass line was blocked and the coolant was boiling out of the overflow hose on the tank but i don't know. dose anyone have any ideas as to how I might be losing the coolant? For the amount I am losing i would think that a hose is leaking but I don't see a steady leak anywhere on the ground. Is there a way to check the bypass line to see if it is clear? thanks
 

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4,166 Posts
Consuming coolant is one of the early signs of head gasket failures. However, sometimes heater hoses develop a tiny leak and drip coolant right onto the hot exhaust manifold, making it impossible to find. If you open your hood when the car is hot and you smell coolant, this is usually the case.
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,105 Posts
The purge line (not a "bypass") should flow a small steady stream back to the top side of the surge tank.

If you study the sticky poll on head gasket failures in the Engines; Northstar forum you'll see that 1999 was the worst year for failing cylinder block head bolt hole threads.

To rule out that possibility rent a cylinder block exhaust gas test kit from a parts store and follow the instructions - don't try to make it better with long bubble times.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,509 Posts
the TWO things you should check/do BEFORE doing ANYTHING else -
1) check the PURGE LINE for a constant - gentle - flow of coolant -

2) do the BLOCK TEST -

both have been discussed a million times - google them for details -
 

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1999 Deville
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35 Posts
Discussion Starter #5
checked the purge line and it is not blocked. Coolant flowing into the tank. Whenever I check the coolant level in the tank the day after I drive it I gotta add coolant. I t 's gotta be leaking from somewhere. I'll do a block test next and check that bolt hole. thanks
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,509 Posts
checked the purge line and it is not blocked. Coolant flowing into the tank. Whenever I check the coolant level in the tank the day after I drive it I gotta add coolant. I t 's gotta be leaking from somewhere. I'll do a block test next and check that bolt hole. thanks
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keep in mind that when the surge tank is "FULL" it is actually about half-full -
 

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1999 Deville
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35 Posts
Discussion Starter #7
Ok folks, there has to be an explanation for the amount of coolant I'm losing each time I drive. I'm like having to add at least a qt driving just 30 miles but for losing this amount I would be looking for a leaking hose but I don't see any hoses leaking and there are no puddles of coolant under the engine. coolant is flowing at a very good rate from the purge line. I am completely baffled at this point.The coolant must be leaking while driving, but from where?
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,975 Posts
Have you done a block test as advised? Chances are the coolant is going out the tail pipe.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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As posted, to what level are you filling the surge tank ? Correct level is 1/2 to 3/5 full, COLD. Coolant expands a lot when heated, and that expansion acts against the airspace in the tank and the pressure cap setting to create the system pressure that assures "solid' coolant to the water pump and also raises the boil point. If the coolant is at or near the top of the tank/filler neck it simply flows out of the overflow tube every time the engine warms up - until the coolant creates its own happy level. If the level was correct it should take about two more quarts to fill the tank to the top.

Note the FULL COLD and flat arrow legends molded into the top of the surge tank.

I took the liberty of adding your 1999 Deville to your username banner. Much easier to see now - than going back to Square One every time.

Deville 2000 reservoir tankside.jpg
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,509 Posts
Ok folks, there has to be an explanation for the amount of coolant I'm losing each time I drive. I'm like having to add at least a qt driving just 30 miles but for losing this amount I would be looking for a leaking hose but I don't see any hoses leaking and there are no puddles of coolant under the engine. coolant is flowing at a very good rate from the purge line. I am completely baffled at this point.The coolant must be leaking while driving, but from where?
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once again - WITH MORE FEELING -

DO A BLOCK TEST -
you can "rent" the test kit for free from most large auto parts stores -
just pay for the magic blue juice - less than $10
 
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