Overheating - sometimes it really is just the radiator.

Story of a problem solved. 

The car is a 42 Commodore 8. Nice original with restoration and HET club participation from around the 1990s. 

Runs good, but runs HOT. 200 degrees measured with a thermometer. (not 210, not 220 but just 200) This was on a 100+ degree California day.

Hummmmm. . . . maybe somethings is wrong or maybe it just doesnt have any reserve capacity for the summer weather(?)  Try it again when the the air is a cooler 60 degrees and STILL it's idling at 200 degrees. 

 Its running a 180 thermostat. Switch to a 160. Still goes to 200 

 Tear into it. 

The heat riser is stuck closed. OK, that will certainly get it hot quickly. Take it apart, open it up and block off the pathway to stop/slow the exhaust gasses. Still running at 200, but now it takes a little longer to get there. 

 Open the cooling system.

Filled with 100% green antifreeze. (the car is from Maine, guess they wanted to make sure it didnt freeze) 

Remove the water jacket. It looks brand new NO RUST! (hurray!) the water passages in the block are as clean as the outside of the engine. (how often do you see that?) 

Pull the temp sender and put a bore scope into the head, its as clean as the block. 🙂

 Send the radiator out and the old experienced guy at the shop flushes it, but because of the design and the small leaks on the surface of the core he did not want to attempt to rod it out. Reinstall the radiator and of course its still idling at 200. 

 Its gotta be the radiator. . . what else could it be???

So pull it again and tell the radiator guy to put in a new core. 

New 4 row core. $850(!)  <ouch>  But hey is IS a huge prewar radiator. . . .maybe I should have asked for my old core back? it was probably valuable as scrap copper. 

Anyway, today I installed the new radiator and whatta ya know, idling at a perfect 160. 

As much as people fight overheating and cooling system issues, sometimes it really "Just needs a radiator". 

Not cheap, but the cost was much easier to bear after I see it working well. 


  • Glowplug
    Glowplug Expert Adviser
    Glad to hear about your success!
  • Huddy42
    Huddy42 Senior Contributor
    My 1942 6 cylinder never gets overheated, all original car 31K miles, I do thou run a six blade fan. On the hottest of days runs around 170/180 deg 
  • 200 isn't that bad especially on a 100 degree day.  check your timing , make sure it is not retarded. Check your points too,  if the gap closes up it will retard the timing.  Used to run an irrigation pump on the farm, if it had antifreeze in it it would run hot. we drained out the antifreeze and put just water in it, ran cooler.  
    Good luck.
  • Geoff
    Geoff Senior Contributor
    It won't run cooler when the rust particles clog up the radiator.
  • 37 CTS
    37 CTS Senior Contributor
    My 37 Hudson Eight ran hot and was not run above 80F ambient temp. And I found the radiator was the problem. When the radiator with a new core was installed I drove it at 106 degrees.    Also in my 1941 Super Six , the rebuilt radiator made the car run its best.
  • Geoff
    Geoff Senior Contributor
    Remember, adding anti-freeze/anti-boil will raise the temperature slightly, which is nothing to worry about.  Better to use this than to have corrosion going inside the system.  The compound raises the boiling point of the coolant, as does pressurising the system.    It doesn't matter how hot the engine gets, providing it is not boiling and forming pockets of steam, and does not lose water. My 1928 Essex runs just below the red line normally, but never uses water.