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Head Gasket Diagnosis Please Help


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Hello there, I have a 98 Deville and was diagnosed a few months a ago with a blown head gasket. I took it to get checked out because it sent me a message telling me to shut off the engine before it overheats. Just to quickly bring you up to speed it happened a couple times. I changed all coolant out, changed t-stat, flushed and filled the rad and changed out the rad which had a crack in it. After I exhausted all efforts I took it to Pep Boys. The mechanic was not the best place to take a caddy but at the time I didnt know where else to go I only assumed it was a minor problem. The car has been sitting for about four or five months and I have posted before many times about this topic fishing for information and had great responses.

I was told to perform a series of test and here are the results. I have performed a cumbustion gases test which did not test 100% positive but the liquid barely started to turn yellow. I have performed a leak down test which tested negative. Finally over the past weekeend I changed the t-stat now the car is running great (i had an autozone t-stat prior to this in the car). I drove the car in stop and go traffic and got on the interstate for about 90 miles with speeds ranging from 60-85. The temperature outside when I was having the problems was about 75-95 degrees, now its winter and the temp. here lately is about 20 degrees. My questions are could the outside temp being so low prevent me from overheating thus hiding the blown head gasket, could it have been a t-stat the entire time and lastely if someone could possibly post what the normal operating temp should be on a 20 degree day on a highway.

You guys have always had some great info and I thank you for that. I appreciate you reading this today and if all possible could someone please help I was on the verge of yanking the motor and replacing gaskets and retapping the block. Im at a loss now what do I do?

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....I was told to perform a series of test and here are the results. I have performed a cumbustion gases test which did not test 100% positive but the liquid barely started to turn yellow.

If that was a NAPA test kit, read the instructions three times and perform the test again. There should be no ambiguity in your results.

....Finally over the past weekeend I changed the t-stat now the car is running great (i had an autozone t-stat prior to this in the car).....could it have been a t-stat the entire time....

YES. Aftermarket parts are not perfect mates for modern engines. IF you installed an OEM part purchased at a GM dealer's parts counter, you have the correct thermostat.

....and lastely if someone could possibly post what the normal operating temp should be on a 20 degree day on a highway.

The external ambient temperature will not be a factor when your engine cooling system system is operating as designed. With an OEM thermostat installed, engine coolant temperatures will fluctuate somewhere between 198 and 220 degrees F as the thermostat responds to the engine temperature changes. This action happens constantly, and so rapidly, you might not see any engine coolant temperature indication change on the dashboard.

There are several other factors involved when the external ambient temperature is in the 90's.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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I have performed the combustion gases test about 10 times. The fluid turns a bluish-green and won't draw air after about 5 pumps on the aspirator bulb (which is only about 25 seconds). The test instructions asks you to pump the bulb for about a minute and if the fluid stays blue or aspirator will not pump for a minute then a leak is not present at the time of the test. So to me the test is a little confusing. I have watched a ton of videos on the combustion test and the test operator never has a problem. This is the Napa test kit and its results are always either a yes or no but in this case Im not sure.

JimD, Thank you for the response and if it weren't for this site that caddy would be sitting in the driveway completely inoperable right now.

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Read this thread through, there is a lot of info there that will be of help to you

http://caddyinfo.ipbhost.com/index.php?showtopic=35117&pid=182088&st=105entry182088

At the end of that thread is a link to testing your Northstar from Northstar Performance, do that test and see if she overheats

At the beginning of a bad head gasket, it can be difficult to determine a bad HG, those NAPA testers are not sensitive enough at the beginning

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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