: couple of cooling sistem questions

07-09-08, 01:18 PM
I bought a í98 Deville a couple of months ago. I just came back from a 800-900 mi trip and the next day I got the message Check coolant level.
I added a bit more coolant (the green one, because thatís what I have in it). My question is: is it possible that the coolant level to drop without any visible leaks? Now I want to change the coolant with the orange one. Should I flush with water first or just re-change it in 6 mo? Should I use some of the tabs? If so, what kind? How many? Where should I put them?
Whatís the best, easiest way to change the coolant?
Thanks much!

07-09-08, 02:45 PM
:cool: For the past two months there has been an endless stream of cooling questions, diagnoses, change info, and replies to DEXCOOL or low-silicate green A/F. Go back through this forum and up in Deville.....open threads of interest....there are several methods of drain and refill used, some with diagrams, all with recommendations.

I have typed out the instructions twice in the last 48 hours. So have several other Northstar owners. Search..........

07-09-08, 02:56 PM

07-09-08, 04:23 PM
My question is: is it possible that the coolant level to drop without any visible leaks?
Yes. Could be a small slow leak that evaporates before you can see it or it could be a head gasket and the coolant is being ingested.

07-09-08, 05:25 PM
is there any way i could find out (gasket) without going to a shop ?

07-09-08, 07:34 PM
Yes, have the coolant tested for the presence of exhaust gases. You can but a kit from Napa and do it yourself. You can also do a cylinder pressure test if you have a compressor. Tech Tips section has a tutorial.

07-10-08, 08:06 AM
At this point there is no clear advantage to flushing and going back to Dex.
If you are satisfied with the green stuff just use that.
Nothing wrong with going back to Dex either, just no reason to do extra work to switch back.

Those have lots of places where they can have small leaks that are undetectable from the top.
The coolant crossover seals could be leaking, the pump cover, water pump and yes... the dreaded head gaskets.

Pressure testing and thorough inspection would be a good idea before you worry about chasing Head Gasket issues.
Usually HGs will manifest themselves in other ways besides just a falling coolant level.
Overheating at highway speeds and a cold start misfire are the most common.