I have a 1999 base Deville and I have a couple questions about servicing the cooling system and the tranny.

I just bought this car and it is my first Northstar. Is it true that my tranny has no replaceable filter? Is a flush all it needs?

The dealer wants $212 to flush my cooling system and they also replace the thermostat. Is this a fair price?

I am one who have always done my own service but with the fear of a blown head gasket I want it done right. Any thoughts?

Just drain and refill the cooling system with a 50/50 mix of Dex-Cool and distilled water. Add the suppliment tabs to the radiator hose, not the syrge tank. No need to flush it.

There is a filter in the 4T80E trans but it is deep inside and only gets changed during a rebuild. There are two reusable screens in the pan. Click on the Technical Archives at the top left of this page and read up on trans flushing. :tisk:

Just drain and refill the cooling system with a 50/50 mix of Dex-Cool and distilled water. Add the suppliment tabs to the radiator hose, not the syrge tank. No need to flush it.

There is a filter in the 4T80E trans but it is deep inside and only gets changed during a rebuild. There are two reusable screens in the pan. Click on the Technical Archives at the top left of this page and read up on trans flushing. :tisk:

Thanks for the quick reply. I did an extensive search on these forums and read several posts on tranny service and I am getting mixed results. I really don't know what to beleive. Some say don't flush and some say flush. What I really want is enough people to post one way or another to get a concenus on what works best. I can appreciate everybody's opinion equaly.

My local Cadillac dealer says flush and wants $200 for it. Jiffy Lube wants $110. I have zero problems paying the $200 but I want to know what I am paying the extra money for. Does the dealer use better equipment? Different fluid? I feel I can find this out by seeing other people's experiances at different places. I cannot do this service myself because of my size. I cannot fit under my car even with jack stands.

As a forum moderator at another website catering to computers I can appreciate the need to do an extensive search before I post. Rest assured that was done. I just wish there were more posts/articles swaying me one way or another.

Well, the dealer wants $200 for a flush, that is why they recommend it. The Technical Archives at the top of this page that I suggested you read was written by a well respected former poster who is a GM powertrain engineer. We pretty much take that as gospel.

Well, the dealer wants $200 for a flush, that is why they recommend it. The Technical Archives at the top of this page that I suggested you read was written by a well respected former poster who is a GM powertrain engineer. We pretty much take that as gospel.


Thanks for that information. It will help me decide.

I am one who have always done my own service but with the fear of a blown head gasket I want it done right. Any thoughts?


My thought is if you want it done right do it yourself!:stirpot:

The recommended is not to flush. Drain and refill. That applies to trans and cooling system.

You still have to drop the pan on the trans. There is a plug to drain the "top" of the trans. There are posts with better instructions. The plug is 10mm and I believe it's hidden by the filter screen.

In addition, even some flush eq mfg's don't recommend a flush if the mileage is over 100K.

My Factor Service Manual states that you need to replace the gaskets of the pan after dropping the pan and draining the trannny, recommends replacing the screens.

Unless they changed something, the gasket on my '97 was reusable and the screens can be flushed and reused although they where as clean as new. The only thing I replaced was the fluid.

Thanks for all the input guys. I am going to find a reputable pleace here in Denver and have them drop the pan. I have always done this myself but I am unable to do it right now. Anybody in Denver that has a good reputation?