Ready for advice

[flaglor]

So, after much study of the discussions on this site, I bought a 1999 STS. I bought it from a friend, who is the original owner. It has 136,500 miles right now. The original engine had the gasket go bad at about 120,000 miles. He bought a used Northstar with 86,000 miles, and had it installed by the Cadillac dealer. It went fine for another 15,000 miles, then started running rough at start up, so he parked it. So we have an engine with approx. 100,000 miles right now.

I bought it knowing all about the issues. The remainder of the car is perfect. Garaged all its live, and it looks and smells like new. I have driven it about 1000 miles in the last 3 weeks, watching carefully for signs of problems. It was my intention to do the Northstar Performance mod. and keep driving for a long time. Problem is, I can't decide if I have a problem or not.

The only issue is that when you start the car, cold, there is a miss that lasts for about 20 seconds. Once that is done, it goes fine. I have been watching coolant since I picked it up. Not using any that I can tell. The temp. gage stays at 1/2 (analog gage), and only very occasionally goes above it. One time it went to 5/8 scale, but only momentarily. Outside temps. here have been 90+ consistently. No coolant smell from the oil sump. No exhaust discharge. In the morning, when the engine is cool, there is a little pressure in the coolant resevoir when you loosen the cap. Not a lot, less than when you open a 2 liter coke. If I didn't know about the potential problems, I'd say I have no problem.

Any advice? Barring any changes, I guess I'll just keep driving it till I see a reason to stop. It's pretty sweet!

Thanks,

Tom

[BodybyFisher]

That miss to me is suspect, but you do not seem to be complaining about overheating, but the pressure in the system when it is cold is curious

The miss is what I was getting with a bad head gasket.

I would take the cap off the black tank and smell the coolant, if it smells like exhaust, you have a problem.

You can do a cylinder pressurization test and you can test the coolant for combustion by products to determine definitively if you have a problem. NAPA sells a coolant tester

[Ranger]

As BBF said, you do have a few suspicious symptoms. That said, IF it is a head gasket, there is nothing you can do about it. Just drive it and if the gasket is starting to go, it will let you know in time. A used engine is always a gamble unless you insert the bolt holes or stud it before installing it.

[flaglor]

Well, obviously, it would have been better if the original owner had just fixed the original engine instead of putting in the used one. This is what I have.

I am highly suspect of the miss when cold. I will do the coolant test and see what that tells me. I really expected to see some serious overheating issues, and I have not. I am not losing any noticable amount of coolant.

I guess my question is this: With my symptoms, and assuming a bad result on the coolant test, what are your thoughts about how much more I can drive this engine before doing the repairs? What are the risks of continued operation? This assumes that things don't get any worse in terms of overheating or other issues?

[BodybyFisher]

This problem progresses to the point where it overheats in traffic, then where it overheats at highway speed.... I had the miss for 6 months before the car became basically undriveable, but its anyones guess how long it will take. In addition, I didnt lose much coolant nor did coolant get into the oil

[Ranger]

Keep in mind that in the very early stages the coolant test may still show a negative result.