: How to change thermostat on '79 CDV w/ 425?

08-12-11, 01:53 PM
This is a dumb question. In a forum where guys are doing engine swaps like plugging in a USB stick, I need help changing my thermostat...

The '79 has been running too warm for the longest time. It never gets to the point of overheating, but you can smell "the hotness" when you park after a long drive or a good 85 mph interstart jaunt. It also runs sluggishly, feeling like it has less power than when it's just gotten up to the correct temp.

When there was a temp gauge in it (in car when I bought it, stopped working, no idea how they wired it) it would run at about 220 after driving a while.

If I put in a 160 thermostat, will that help do you think? I have no idea how old the one in there is, or what it's rating is.... never even seen it. Hell, don't even really know where it is. Could someone point it out to me & tell me how to change it?
I'm learning, but I'm still a newbie under the hood.


08-12-11, 02:26 PM
my 69 shop manual (for 472...same block as 425 i believe) says:

drain radiator until coolant is below level or thermostat housing
disconnect upper radiator hose at thermostat housing
remove two screws securing housing to cylinder block and remove housing.
discard gasket.

install is reverse of this.

to find the thermostat, follow upper radiator hose.

08-12-11, 04:03 PM
Thanks, that's basically what I thought. Will try it. Couldn't find it in the '79 manual for some reason.

08-12-11, 04:09 PM
the instructions sounds pretty standard (meaning sounds like just about every other one I've seen) so i'm sure you will not have a problem with it. If you do...atleast these forums are here :D

08-12-11, 08:38 PM
Thermostat is under the AC compressor. You remove the compressor without disconnecting the lines and move it to the side to get to the thermostat. There are pics on my project thread with the compressor moved as I was doing my water pump.

160 is way too cold for your 425. Your water temps sound about right. After driving on the highway, the engine should be cooler than if it were just idling in the driveway (all the air moving across the rad).

08-12-11, 10:50 PM
I use an 180* stat and I love it. It never moves from 185 but I dont have the AC thing in front of my radiator. The Caddy motor was suppose to run at 195.

08-13-11, 07:11 AM
As jayoldschool said,160 is way too cold for the 425.It`s supposed to have a 195 stat.I have a 185 in my '78 Deville 425.I wish these 425`s had a temp gauge.

08-13-11, 09:52 AM
Check your radiator and condenser. Perhaps, there is something like dirt, bugs and debris restricting air flow through the radiator.

08-13-11, 11:12 AM
One more thing. "Hot" doesn't "smell". Oil/coolant leaks have a smell, though, when the liquid burns off a hot engine...