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99 Seville overheating issue


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First let me say this site has been fantastic with my latest adventure. I have read many posts and have received some great info from it. I wished that I would have read this BEFORE I chose to fill a lifelong dream to own a caddy, but here I am and I intend to make this right come hell or high water.

Quick background on the car...bought it off craigslist from a guy that got it at an auction recently 9/2013. He got rid of it, due to it was overheating. I have had "project" cars in the past that have had the same issue and it was in most cases an easy fix. This one has me puzzled. I have had the car for two weeks now. Got it for a decent price and quite frankly am not worried about the money if I can get this to drive as it was intended to when it drove out of the factory. It is fully loaded and everything I have ever wanted to own. Looking for it to be a “weekend” fun drive car. 130,000 miles on the car. Runs and drives extremely smooth and has all the “bells and whistles”. Do not want to give up on the car and want to figure this out. Found a service sticker in the window that shows next service due 10/2008 at 132,000 miles…so this car has sat for 5 years. Also, when I looked at the coolant the mixture seemed to be 100% green, yes I said green coolant. So not the right coolant or mixture.

Ok, so drove it 5 miles and temp gauge goes almost to the red and get the digital alarm of A/C shut off engine hot. Parked it and started the diagnosis. First drained all the coolant I could out of the system. Replaced the thermostat. Replaced the coolant with 50/50 Dexcool. Still ran hot after 5 miles. Took advice I read on here about pulling the hose off of the surge tank looking for flow back into it. Bingo, no flow. Then took the advice from here to check the hollow bolt for blockage. Wouldn’t you know, it and the line going into the throttle was blocked. Started the car again and I had flow. Drove the car around for a few days and no overheating past the “1’o’clock” on the gauge. Three days ago I decided to take it to work(35 miles one way). No issue on the way to work 65 degrees outside. Drove at HWY speed up to 65mph. On my way home a little spike but nothing to worry about. Check to coolant when the car cooled off and it was down a bit. Replace the coolant to the cool fill level. Took it to work the next day, same temp in the morning and no issues. On the way home the outside temp was at 85 degrees. Heated up to the A?C off engine hot level. Pulled over and checked to make sure my fans were working, they were. Turned the car off for 20 min or so and let it cool down. Drove for another few miles at 65 mph and it over heated again. Same process, 20min checked the fans, they were working. Each time it goes past the “2 O’cock on the gauge I loose heat in the cab. Let it cool down and took back roads home. Never got over 50 MPH and it did not overheat. Checked the coolant after I had been home for a few hours and lost a little, maybe a cup. Refilled to fill line. This morning I am off of work. Drove the car on back roads, never getting over 55mph and never over heated. Got on the freeway and up to 65 MPH and it began to rise, never allowed it to get to the A/C off engine hot level, got off and took back roads, kept it under 55mph and it cooled right back down to where it should be.

Took my other car to the parts store to get the tester to test for combustion gases in the coolant and bought a new pressure cap for the surge tank. Will see what results I get from that tonight or tomorrow and will update.

As you can see I have made some headway on this, but am not sure if I should look at other steps before I continue on the path I am on. Do not want to get rid of the car, love the smooth ride and want to get it running right.

Should add that the A/C is not blowing cool and needs to be recharged, but I do not think this has anything to do with this issue. Also and hearing the water noise in the dash once in a while when turning, that others have described.

Thank you for this site and does anyone have any insight?

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First, it's pretty clear that this car was parked five years ago because of an overheating problem. Second, green antifreeze in the car means that it *must* be flushed and replaced every *two* years, not five like the owner's manual says, and short of thoroughly flushing out the entire system (next to impossible without a pull-down, new radiator and heater core, etc.) you will have to service your cooling system every two years even if you use red/orange/yellow long-lasting antifreeze.

Second, your symptoms sound like the classic case of antifreeze going too long (a really big no-no for any aluminum engine), a head bolt or two pulling, and head gasket leakage.

You can get a quick read of the situation by seeing if the exhaust ever has a coolant smell about it, particularly if you shut it off after starting it the first thing in the morning, and also if the radiator surge tank has any hint of a smell of exhaust gases. If either odor is present, your testing will almost certainly show that you have a head gasket problem.

Third, you need to run your OBD codes to see what's up with the A/C and the rest of the car. Turn on the key (don't start the car), and press <Off> and <Pass Warmer> together on the A/C console until all the buttons light up like you just turned on the key, then release both buttons. The OBD codes will be presented one at a time on the driver message screen. The codes will be something like


where the first three letters are an acronym for the module that threw the code, the letter and four numbers are the OBD diagnostic trouble code (DTC), and there will be a CURRENT if the code is still being detected, and a HISTORY if it was seen in the last several weeks but not since the key was turned on. Write these down and post them here.

-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Not too much to add to what Jim has said, and I agree with his suggestions, but here goes.

Check the water pump tensioner and belt, which runs off the camshaft on drivers side front of engine. (left side) Tensioner should move freely and belt should not slip on pully. Sometimes they can get stuck in one spot and not run the water pump correctly at high speed.

Keep checking that hollow bolt for flow. You didn't say what was blocking it, but if it was rubber chunks (like from a coolant hose) there could be more stuff circulating in the system.

It is possible that someone loaded it up with stop leak or some other fix in a can. If that's what was blocking the hollow bolt, it could be blocking other parts of the system (like the heater core) and wreaking havoc in general. See if you can pressure flush the heater core being very careful with the orientation of all fitting and connectors, some only work correctly in one direction.

My old '99 STS was one of the best and fastest cars I've ever owned. Yours is very well worth fixing up in my opinion.

Never underestimate the amount of a persons greed.

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Don't overheating and coolant loss go together? Combustion gases pressurize cooling system and push out coolant and so on? So, ur car is getting hot but not loosing coolant. So do u have a problem? If motor gets so hot that computer shuts off a/c and tells u to stop than I would say yes. It sounds like u have not had car long enough to make it puke out all the coolant yet.

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