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99 deville also overheating driving me nuts!!!!


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it hasn't given me a problem and it has been running nice and cool since then.

Well that's good news at least. It could be the "weird" weather, but I really hope you found the problem. Please let us know.

Never underestimate the amount of a persons greed.

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it hasn't given me a problem and it has been running nice and cool since then.

Well that's good news at least. It could be the "weird" weather, but I really hope you found the problem. Please let us know.

I seriously doubt the weather has anything to do with the problem. My money is the head gaskets are in the preliminary stages of failing since all the other areas have been checked with the exception of the radiator surge tank cap.

One hour spent pressure testing the engine will positively confirm or rule out bad head gaskets....

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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well guys, i finally got the chance to work on theis problem today, i rented a pressure tester, at auto zone and have her pumped up to 15 psi. after about 30 minutes, the guage had moved approximately 1/32 of an inch, almost un noticable, but it is losing pressure non the less., i bought the combustion gases in the coolant kit, and will test that later, for now i am going to leave the pressure on for a couple of hours and see what happens. oh by the way, when i removed the cap from the surge tank, it was down about 1 quart again, so it is losing about a quart a week as far as i can tell. i'll know more this evening, thank's for all the help, and i appologize for not being able to get back on sooner, but i've been working a lot of overtime lately (to pay for all of this stuff!!!!) LOL.

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If the pressure drops and you cannot find a leak, be sure that you pull the plugs before cranking it over, just incase it is leaking into a cylinder. You don't want to hydrolock it. Also watch it while someone else cranks it to see if there is any mist expelled from the plug holes when cranked. That is a sign of a bad head gasket. A quart a week is not a good sign. Let us know what you find and good luck.

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thank's ranger, this may be a foolish question but, where the hell could all this coolant be going?, there is no sign of any steam or smoke coming from the exhaust what so ever, there is no indication that the oil level is "rising", oil is clear and looks like new!!!!! it boggles my mind!!!!!

oh , and the car runs perfect, until i receive the "low coolant" warning, and if i continue driving without adding coolant, the temp will start rising.

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It could be slow leak that evaporates before you see it. Radiator side tanks, water pump cover, surge tank are just a few possibilities. Dried Dex will leave a telltale whiteish residue behind, so keep an eye out for it. Worst case would be the head gaskets. If the pressure drops on your test, you know that there is a leak and since the engine is cold, there will be no evaporation. The leak will eventually have to show itself if you leave it pressurized long enough.

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thank's, i just checked the guage, it lost 1 psi in 3 and 1/2 hours time.

Hmm, there is a leak somewhere, albeit slow. Keep it on there and it should eventually drip somewhere unless it is leaking into the cylinder. If it still doesn't show itself, do a cylinder pressure test. Hopefully, it is just a small external leak.

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You know a component that is not discussed a lot are the heater pipes at the rear of the engine, take a look to see if they are corroded...

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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thank's again guys, update, i pumped her back up again and went to 17 psi, i checked all over and finally spotted the drips!!!!!!, i am almost too embarrassed to admit this, but the reason that i could not see any coolant on the ground is because, i park in nearly the same spot everyday on my old concrete driveway and believe it or not, it is dripping right into the center of the driveway where the expansion joint had long since split apart, the drip was going directly into the crack, there is not a drop outside of the crack on the driveway!!!!!! anyway, from experimenting with the pump, it seems that it only drips when the pressure is at least psi, and it takes about a minute to start dripping from the bottom center of the engine area, it is actually rolling off the front center of the tranny pan lip, (while the front of the car is up on ramps) and when the car is flat on the ground,the drip is coming off of what looks like a 3"X6" black plate with a 3/4" hole in the middle of it almost in the center of the bottom of the engine. i can't see anything above it that is wet, (of course it is difficult to see the back side of the engine). the heater lines entering the firewall area are dry, the surge tank fittings are dry as far as i can tell, the water pump area is dry , so i don't know if i am any better off having found that it is an exterior leak!!!!! i'll keep checking though. thank's again.

dumb den

oh, by the way, the dripping stops when i release the pressure.

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Can you take a photo of it? Where is this black plate, what side of the engine the firewall side? or the Left side? This could be a casting leak. Aluminum castings are prone to small (as in microscopic) imperfections that can be a nuisance in water jackets. If that is what you are experiencing, that is what the cooling supplement is designed to stop.. Have you used the cooling supplement when you have done cooling system work? Please try to describe exactly where the leak is coming from, pictures are great

post-2998-1158884251.jpg

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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The good, make that great, news is that is is external and not a head gasket. Since this is such a small leak, maybe a dose of cooling system suppliment (sealant tabs) will seal it up.

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This IS great news! Good job! I hope you can get a picture of that plate as Body asked, I'd like to see it.

I find it a little hard to believe that you can park your car over that gap in the driveway EVERY time, but I'll take it for now! :)

Never underestimate the amount of a persons greed.

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thank's again guys, update, i pumped her back up again and went to 17 psi, i checked all over and finally spotted the drips!!!!!!, i am almost too embarrassed to admit this, but the reason that i could not see any coolant on the ground is because, i park in nearly the same spot everyday on my old concrete driveway and believe it or not, it is dripping right into the center of the driveway where the expansion joint had long since split apart, the drip was going directly into the crack, there is not a drop outside of the crack on the driveway!!!!!! anyway, from experimenting with the pump, it seems that it only drips when the pressure is at least psi, and it takes about a minute to start dripping from the bottom center of the engine area, it is actually rolling off the front center of the tranny pan lip, (while the front of the car is up on ramps) and when the car is flat on the ground,the drip is coming off of what looks like a 3"X6" black plate with a 3/4" hole in the middle of it almost in the center of the bottom of the engine. i can't see anything above it that is wet, (of course it is difficult to see the back side of the engine). the heater lines entering the firewall area are dry, the surge tank fittings are dry as far as i can tell, the water pump area is dry , so i don't know if i am any better off having found that it is an exterior leak!!!!! i'll keep checking though. thank's again.

dumb den

oh, by the way, the dripping stops when i release the pressure.

I would tighten the heater hoses' clamps before moving further.

The saddest thing in life is wasted talent

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Johnny G,

my wife has always told me i was an extreme "creature of habit", thought she was kidding until now!!!!!!

i'l check the heater clamps, but they appear to be dry

i'll try and get a picture of it in a bit.

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Johnny G,

my wife has always told me i was an extreme "creature of habit", thought she was kidding until now!!!!!!

i'l check the heater clamps, but they appear to be dry

i'll try and get a picture of it in a bit.

Its possible that you are only loosing coolant at 17 PSI, and when it happens the water is so hot and under pressure it vaporizes immediately when it hits the air, leaving no trace. Right now you are pushing out COLD water... its visible

This happens with cracks in the radiator end tanks also, it comes out under pressure and vaporizes, you dont see leaks, but it blows out steam 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/

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

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Thats the exhaust crossover pipe. Hmmm

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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yes i believe that the black piece is some kind of protector, or skid plate of some sotr because it looks like heavy guage steel and doesn't seem to do anything., don't know what the hole is in the center though. with the front wheels up on ramps, the drip seems to be rolling of the topside of the lip of the tranny pan right near the center directly behind the center of that plate.

i can't imagine what could be back there!, tomorrow i will try and get an inspection mirror down in there and see where it begins to get wet.

can i use that "barsleak"?, i didn't think it was compatable with the northstar, thought you had to use the pellets?

on a side note, while i was under there i noticed "bright green grease" flung all over the drivers side area, looks like maybe the inner cv joint boot let go, but i can't find any cuts or rips, and it feels tight, but it looks like all that fresh grease came from the end closest to the engine.

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The Barsleaks comes in two versions, tabs (HDC) or powdered tabs (G12BP).

Green grease is definately from the Cv boot. Check the valley of the pleats. I have had the rip there and it was invisible til I stuck my finger in the joint.

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on a side note, while i was under there i noticed "bright green grease" flung all over the drivers side area, looks like maybe the inner cv joint boot let go, but i can't find any cuts or rips, and it feels tight, but it looks like all that fresh grease came from the end closest to the engine.

Sounds familiar. I have the same problem, outer boot though. Up on a lift I could see the tear on my boot. I looked several times while it was up on my jack, and never saw it. It has to be at the right spot to see it sometimes. I need to replace that half-shaft someday soon, but so far, no noises on a regular basis.

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it must have happened recently, the grease looks new and bright green, i'll have to get it on a lift and check , it almost looks like it came out of the end of the boot near the tranny, but the clamp appears to be tight.

one other problem that i need to bother you guys with, my driver's side mirror is fogged up, and discolored, i was wondering if i can replace just the mirror glass, or do i have to replace the housing too?

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it must have happened recently, the grease looks new and bright green, i'll have to get it on a lift and check , it almost looks like it came out of the end of the boot near the tranny, but the clamp appears to be tight.

one other problem that i need to bother you guys with, my driver's side mirror is fogged up, and discolored, i was wondering if i can replace just the mirror glass, or do i have to replace the housing too?

:lol: How ironic! I just replaced my driver side mirror this summer. I found a like new OEM heated, auto-dimming mirror on eBay for $10.00. The mirror alone retails for $177 or something like that. The whole assembly with the motor is probably outrageous. Watch out on Ebay though, there are a lot of sellers selling plain mirrors. You might find a whole asembly on eBay for cheap, and just use the glass. They seem to go for around $25 or so.

Be careful when popping the new mirror in. There are 4 "legs" that come off the motor that you have to be careful with. Grease the center post with a little grease and it should pop on fairly easy. I tried with no grease at first and had a fit.

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