RUNNING HOT..after doing good stuff
 

So, my 39 Merc cools great, no issues. My passenger side waterpump was flinging coolant, so I did the following: sent the waterpumps to Skip for his well known excellent rebuilds, pulled the radiator and took to the rad shop. When removing the radiator I found there were no thermostats so I got a pair of Shewman high flow thermostats. The shop said the radiator flowed well, no repairs needed, just flushed out thoroughly. So I reinstall all of the above along with new lower hoses and filled with coolant, started her up and if allowed....it will RUN HOT! I have briefly run/driven it an was able to add some additional coolant, I do not believe there is any kind of air in the system. Just came back from brief drive, going to let things cool, and I believe I'm going to pull the stats. What do you guys think??

Shoebox

Re: RUNNING HOT..after doing good stuff
 

Did the rad shop take the tank off.
Lawrie

Re: RUNNING HOT..after doing good stuff
 

Also, what are you calling hot? 190, 200, boiling?

Re: RUNNING HOT..after doing good stuff
 

Probably not, but any chance you put the thermostats in upside-down?

Re: RUNNING HOT..after doing good stuff
 

Thanks for the questions..... no, the shop did not remove the tank. The only temp gauge is the original and previously would not go above "N"ormal. The needle gets to N fairly quick and then moves rapidly higher. The stats are 180 degree. I think this might be the excuse I need to buy a temp gun, but for now that's as precise as I can be.

Re: RUNNING HOT..after doing good stuff
 

Suggest that you check the stats to make sure that they are opening. Drill a couple of 3/16 dia holes in each stat. This will allow the air to escape as you are filling with coolant. May run hotter now that you have stats to control the temp. Should run at 185 degrees minimum. Just my thoughts!!!!!!

Re: RUNNING HOT..after doing good stuff
 

I'm thinking along the same lines as Art. Seen that more than once.

Re: RUNNING HOT..after doing good stuff
 

You DO have a fan on it don't you? LOL Really, I would think you should have the core rodded out.

Re: RUNNING HOT..after doing good stuff
 

Where did you install the stats? Up by the radiator or down by the head? From my experience, when installed up by the rad it takes a while for the heat to reach the stats to open, so the temp climbs. Unless you have holes in the stats.

Re: RUNNING HOT..after doing good stuff
 

Again thanks for all the excellent questions. I do have the stats facing correctly, the Shewman stats have 4 small holes, and they (the stats) are located up by the radiator per original. I verified operation prior to installing.

Re: RUNNING HOT..after doing good stuff
 

I believe it always prudent to change ONE thing at a time.
At this point, I'd suggest you remove the thermostats and see the subsequent result.
Do you have a hot water heater? If so, be certain the valve is all the way open. Remove the radiator cap and allow the engine to climb to operating temperature. Then, "rev" it up a bit. Shut it down, allow to cool.
You need to be certain all of the air is out of the system. I've never had a flathead that got air pockets but others have claimed they did. I suppose it's possible.

Check coolant level - should be covering top core plate. Install cap and see what happens...

Re: RUNNING HOT..after doing good stuff
 

Are you using an original temp. guage? They are not always accurate On my'48 when the guage is 3/4 of the way over, I get 160 to 165 on a laser thermometer. I'm running 160 degree stats.

Re: RUNNING HOT..after doing good stuff
 

You say you have Skips pumps.
As I recall in order for his high flow pumps to work properly he says NOT to use thermostats.

Re: RUNNING HOT..after doing good stuff
 

Believe he is using the stats GM recommends. Seems to me we are all attempting to solve a problem we don't even know exist. The original temp gauge indication is somewhat meaningless without checking the actual temperature. The question is, how do you know it is overheating if you have no idea what temperature it is running at? :)

Re: RUNNING HOT..after doing good stuff
 

If it isn't boiling over, it isn't overheating has been my experience.

Re: RUNNING HOT..after doing good stuff
 

What 'deuce roadster' said....

Re: RUNNING HOT..after doing good stuff
 

I also have a 39 Merc. On your rad does the overflow come off a bump on the top centre of the top tank. are you trying to use a 4 pd cap. that combination will not work.The overflow tub should come off the rad neck.

Re: RUNNING HOT..after doing good stuff
 

have you called Skip to see what he has to say?

and if you remove the radiator have them remove tanks and rod it out. a flow test is not a true indication of how clean the radiator tubes are.....

Re: RUNNING HOT..after doing good stuff
 

I suspect the gauge as well. With no stats and a proper cooling system the gauge should have read cold all the time unless outside temp was above 70. Should have been having trouble getting any heat from heater in cool weather.

Re: RUNNING HOT..after doing good stuff
 

I'm with Donald1950 on this one