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'55 Coupe DeVille overheating problem

Started by njones68, June 08, 2018, 12:42:14 PM

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njones68

After a long and total restoration my '55 Coupe Deville is on the road. However all is not well, the car overheats when driven normally in town. Everything is either new or rebuilt, water pump, thermostat, rad cleaned at the shop and pressure tested,   block hot tanked during the rebuild process, timing to spec, all new hoses etc. etc. It will idle all day and the temperature stays normal, sender good and calibrated with an infrared thermometer, runs at 185' at idle. ( 165' thermostat ) no apparent air locks as the heater blows hot air. Correct AC6 rad cap.

When I drive it normally the temperature rises steadily and goes to the high end of the gauge, I pull over let it idle and it quickly drops back, as soon as start driving it rises again. It is marginally better if I gear down and keep the revs up.

I'm pretty much stumped, everything looks perfect but the problem persists. any ideas?

Dan LeBlanc

Perhaps a timing or lean burn condition causing the car to run a bit hotter than normal.

When you say overheats, are you talking steam coming out from under the hood and coolant boiling over or just a high reading on the dash guage?  Have you checked actual temperature with an infrared temperature gun to see what the temperature is when this occurs?
Dan LeBlanc
1977 Lincoln Continental Town Car

Jeff Rosansky CLC #28373

#2
As Dan says, do you really think it is overheating? My 1st thought was that maybe your regulator was off and overcharging the system. 15 or 16 volts instead of 14 would make the gaugeread wrong..... however you say if you gear down it is better so that may be wrong. 
I would suggest plugging all vacuum ports including the brake booster and see if you still have the problem. There are vac lines that go places you don't even realize.  For example, I really thought I had all vac lines plugged other than the wiper motor which I replaced last week. We pulled the radio out today to see if we could figure out how to repair it. Literally 20 minutes ago my son took the car. He started it and we could hear a vac leak from 1 of the radio vac lines. As I said I thought we had them all plugged but obviously not.
Jeff
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

Bob Schuman

Does your lower radiator hose have a metal spring inside? If not, the increased pump suction at higher engine speeds can suck the hose almost closed and greatly restrict water flow. Another cause can be retarded ignition timing causing the engine to run hot, especially under load.
Bob Schuman, CLC#254
2017 CT6-unsatisfactory (repurchased by GM)
2023 XT5

Caddy Wizard

#4
Here are some things to look at:

1. Vacuum advance unit on the distributor has failed, so while the ignition timing at idle is fine, it isn't advancing the timing enough to keep the engine from producing too much heat at cruising speed.  Check for proper function.

2.  Thermostat is opening, but doesn't open wide enough to allow high volume of water through at cruising speeds. Try a Motorad brand of thermostat.

3.  Radiator is partially plugged, despite being boiled out at a radiator shop and you are not getting enough water through it to keep up at cruising power levels. You could do a very rough test for this by disconnecting the lower hose (when cold!) and covering the outlet from the hose.  Observe how fast the water rushes out of the lower pipe of the radiator.  It should gush out pretty fast.

4.  Water pump impeller is corroded to the point of not pumping high volume.

5.  Belt is slipping badly.
Art Gardner


1955 S60 Fleetwood sedan (now under resto -- has been in paint shop since June 2022!)
1955 S62 Coupe (future show car? 2/3 done)
1958 Eldo Seville (2/3 done)

njones68

I did ckeck the temp with a infrared thermometer, with the gauge at mid point the temp is 185' which is correct. Both upper and lower hoses have springs in them but will check anyway when hot, will also check the vacuum issues, have had wiper motor problem so will start there plus will check the advance.

Thanks all fro the suggestions.

Jon S

I would try advancing the timing 2 degrees further than specification.
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

walt chomosh #23510

my experience with cooling systems and 55 in particular (I won and drive one) is that the 55 is GREAT as is! (as Art said,running garden hose water into the top of the radiator should lead to water running out the bottom at the same volume indicating no restrictions) Now on the other hand, if the motor starts starving for fuel it will get hot fast and even overheat! (idle could be OK) And, ignition timing (proper advance both mechanical and vacuum) simply MUST be working properly for a happy motor which leads to a cool motor.....my 2cents....walt...tulsa,ok

jaxops

...do check your heat riser to see if it is stuck pushing exhaust under your carburetor.  Make sure it the valve can operate, or remove it!!
1970 Buick Electra Convertible
1956 Cadillac Series 75 Limousine
1949 Cadillac Series 75 Imperial Limousine
1979 Lincoln Continental
AACA, Cadillac-LaSalle Club #24591, ASWOA