68 Deville Dash temperature gauge

[Pmartin2204]

So I am going to take my project out for a test drive finally but before I do so I have a question about my temp gauge on the dash. My motor has been swapped with a 1975 472. I know it has the sensors on each end of the heads as well as a sensor behind the water pump. Does the one behind the water pump run the gauge on the dash or do I need to install one where my thermal switch is or perhaps on the other head in the same spot? The gauge when I turn it on goes all the way to the H but when I start it it goes all the way to the c and stays there even after the engine is warmed up. Thanks guys

[Cadillac Fleetwood]

A 1975 engine for a RWD car is a 500, not a 472.  1968 was the last year for a temperature gauge.  Thereafter, there were only lights.  The sending unit that operates a gauge is different from a sending unit that operates a light, and that's the likely reason for your "false" readings.  I owned a 1968 CDV that I drove daily for many years.  The temperature gauge registered just below the 1/4 mark, day in and day out for 15 years under normal operation, and never quite reaching the 1/2 mark under the most adverse conditions.

-Charles Fares

[Pmartin2204]

Thank you Charles. I believe the motor is stamped 1485200. Either way I'd like to utilize the dash gauge if possible if anyone has any advice. I've been searching the threads on here and found a few so I will continue reading.

[bcroe]

That 500 engine from 1975 should not need the premium grade fuel
used in the 60s.  Bruce Roe

[The Tassie Devil(le)]

You will need to replace the later model sender unit with a '68 Sender Unit, and that should work.

Not adviseable to use the cylinder head end sensors as they only operate as a switch and not for a gauge.

Bruce.

[Pmartin2204]

From the threads I read they were saying the same thing but I don't recall them saying anything about swapping the sending unit. I probably just missed that part but thank you kindly to you who took the time to point me in the right direction. I think I can handle it from here and I'll let you guys know the outcome eventually.

[Pmartin2204]

Alright so I'm not quite done with this post yet. My last question before I attempt to get the gauge functioning is does anyone have a picture of the temp sensor I need? There is one on the motor but as you guys said it may not be the correct one. The one that is in the motor right now has two holes on the end of it. Thanks again guys.

[MikeLawson]

The correct temperature sending unit for your car is available from LectricLimited:

https://www.lectriclimited.com/vehiclesearch/result/index/year/109/make/24/model/60?cat=867

The temperature gauge in my '67 DeVille always read too high because the original sender had been replaced with a "generic" part that did not have the correct resistance characteristics. Once I replaced it with the unit I got from LectricLimited, the gauge read exactly how it should as described in the owner's manual.

[Pmartin2204]

Hey guys. Another quick question since the motor in my 68 was swapped at some point to a 500, is this a good thing? I would much rather have the original motor unless someone could point out some benefits. Thanks again.

[The Tassie Devil(le)]

Firstly, as they say, there is no substitute for Cubes, plus, the later engine was designed to run on unleaded petrol, and petrol of a lower grade.

The only "down-side" could be the lack of compression, thereby reducing the power and torque of your original motor.

Bruce.

[Pmartin2204]

So if I understand, Bruce, the motor I have now can run on pump gas  but at reduced power compared to the original motor?

[The Tassie Devil(le)]

Yes, your original motor would have had to use Super grade Leaded Petrol, and now can run on 91 Octane, or even lower Unleaded Petrol with no problems.

Plus, if you intend to rebuild your 500, then you can either go for the 1970 Pistons which were higher compression, and not have to modify the valve seats to run without lead in the fuel.

Externally these engines are identical.

Plus, in real-time driving, you probably wouldn't be actually aware of the power difference, as the reason the 472 was swapped out in the first place could have been because it was worn out.

Bruce.

[Pmartin2204]

Most excellent Bruce! Thanks for the information. I love this forum. You guys rock!

[bcroe]

I have seen more than one high compression engine, that broke a piston
because the driver tried to run it on regular.  I drove 10.75:1 in the 60s,
when good leaded premium was only a penny more than leaded regular. 
I got rid of all those engines when the best premium was not good enough
for them, and cost was headed for an extra dollar a gallon. 

Now I run way more cubes, on crap unleaded, no pinging.  And with a better
transmission and axle ratio, mileage is actually better.  And maintenance is
way down.  Bruce Roe

[Pmartin2204]

Doesn't seem so bad now after. Can't wait to get it registered in the next few weeks.