I changed out the coolant temp sensor. They could have made that a "tad" easier to access. I will keep you posted on this.

 

https://www.cadillacforum.com/forum/...ead.php?t=8758



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Sounds like a headgasket to me. I have two 97 Cadillacs with the northstar. At some point the headgaskets went on them. The problems I would have were I would be driving and sometimes the car would just randomly overheat for no aparent reason. Saw no coolant leaks but had to add some every time it would get hot. I could drive it at times with no problems at all and other times the temp would creep up then redline. Tried things like thermostat and waterpump with no difference in temp control. I have rebuilt bothe engines myself since then and have had no problems. It just sounds like your scenario is similar to mine. Sorry.

 

I will keep you posted on this ordeal. So far so good.

The temp gauge seldom creep up toward redline, they were out of the blue sudden jumps. The crazy thing is that on a couple occasions that I after shutting the engine down I would immidiatly re-start and the temp would very quickly drop right back to the normal 12 o clock position.

Concerning the reply a couple up from here, that is scary, putting the right sensor in the wrong hole. I did refer to the manual for location and when I got her loose coolant... hot coolant did spray out ... all over my hand and arm. I did get the right sensor hole though. Thanks for that heads up.

 

I forgot to ask a second ago... Is it a tremendous ordeal to replace head gaskets on this engine... before a major failure?

 

let me put it this way ........ I will junk the Northstar and replace it with a salvage engine long before I consider doing that.

To add to that, I hear that the failure rate after headgasket replacements is over 50%.


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I saw that actionjackson above said that he replaced them in two of his engines and was wondering about it.

A person also runs the risk of a salvage going south as well.

From what years of Cadillacs can a replacement enigine be put into a 98 STS?

 

The risk of a tested salvage is minimal. Much MUCH less then 50%.
They can also be had for less, much less than the cost of doing a headgasket job.

do the math.


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I have done 2 of these before. Mine was a 97 deville and a 97 seville. It is alot of work to do it. I only did it because I am a mechanic and had access to the special tools needed to do it and a shop to do it in. It cost me about 500 in parts to do it myself and this was also with a discount on parts. To have the headgaskets replaced in a shop you might as well get rid of the car. I have been told as little as $2500 and as much as 4500 depending on what needs to be done. The worst part is that when the headbolts are removed it takes the threads out of the block most of the time. So you have to drill, tap, and timecert(more less a helicoil but special) the block. Lots of work and the tool alone costs about 500 to buy. Engine has to come out the bottom with trans and whole subframe to do the block work. The nice thing is once that is out you can do the whole thing on the subframe. I did one of mine about 2 years and 40k ago and the other one about a year and 20k ago. They both have been great and no overheating at all. If you look for a motor used make sure you match the vin code. If its in an sts it has the 9 code and a sls or deville has the y code. Different cams I believe.

 

Also have never come across a warped head on northstar myself either. And my 97 Deville was overheated really bad a few times before doing the headgaskets. Didn't do anything to the heads except for cleaning them up a little that's it. Mostly just gaskets to do the job.