Temperature experiment- ‘46 Mercury

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Bruce_MO

Well-known member
Temperature experiment- ‘46 Mercury

I finished restoring my ‘46 Merc several months ago, and I was a bit concerned about the temperature it ran at. Motor was completely rebuilt, recored radiator, new pumps from Thirdgen (Ecklers brand), and 180 degree t/stats. It would go to the far right side of the green bar on the gauge (see photo), and would climb steadily approaching “hot” at a light. This was at 80 degrees ambient after a 3-5 mile drive. My infrared gun showed 195 degrees in the top tank. I recently pulled the t/stats and tested them on the stove, and they were fully open at about 180 degrees. But 100% open still made for a significant flow restriction. So I left them out and have been driving it with no t/stats to see what I get.
Today, after a pretty hard 10 mile drive at 70 degrees ambient and a few hills to climb in 2nd gear, you can see in the photo where the needle is. Down a long grade, it went a bit left of the midpoint. So without the flow restriction, I’m seeing significantly lower temps. I wasn’t really expecting that much of a difference.

I’m sure there are many of you who’d say if it isn’t boiling or pushing out coolant, don’t worry about it. But I’d rather have more breathing room before it gets hot. Just makes the drive more enjoyable. Maybe I’ll try 160 degree t/stats next.

Just my experience that I thought I’d share… your results may vary.
 

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Re: Temperature experiment- ‘46 Mercury

Bruce_MO said:
I finished restoring my ‘46 Merc several months ago, and I was a bit concerned about the temperature it ran at. Motor was completely rebuilt, recored radiator, new pumps from Thirdgen (Ecklers brand), and 180 degree t/stats. It would go to the far right side of the green bar on the gauge (see photo), and would climb steadily approaching “hot” at a light. This was at 80 degrees ambient after a 3-5 mile drive. My infrared gun showed 195 degrees in the top tank. I recently pulled the t/stats and tested them on the stove, and they were fully open at about 180 degrees. But 100% open still made for a significant flow restriction. So I left them out and have been driving it with no t/stats to see what I get.
Today, after a pretty hard 10 mile drive at 70 degrees ambient and a few hills to climb in 2nd gear, you can see in the photo where the needle is. Down a long grade, it went a bit left of the midpoint. So without the flow restriction, I’m seeing significantly lower temps. I wasn’t really expecting that much of a difference.

I’m sure there are many of you who’d say if it isn’t boiling or pushing out coolant, don’t worry about it. But I’d rather have more breathing room before it gets hot. Just makes the drive more enjoyable. Maybe I’ll try 160 degree t/stats next.

Just my experience that I thought I’d share… your results may vary.
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573374
 
Re: Temperature experiment- ‘46 Mercury

Here’s a photo. No markings on them. When I tested them in water, they opened up about 1/4”. I’m pretty sure they came from Thirdgen. They functioned fine, but they just didn’t leave enough breathing room when I stopped at a light or for gas.
 

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Re: Temperature experiment- ‘46 Mercury

Bruce_MO said:
Here’s a photo. No markings on them. When I tested them in water, they opened up about 1/4”. I’m pretty sure they came from Thirdgen. They functioned fine, but they just didn’t leave enough breathing room when I stopped at a light or for gas.
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573382
 
Re: Temperature experiment- ‘46 Mercury

The lower 70 degree ambient temp. makes a huge difference. Try it again at 80.
 
Re: Temperature experiment- ‘46 Mercury

I took the challenge… it’s sunny and 86 degrees now. Photo shows steady state at 32-35 mph on a level road after a few miles to reach temp. It’s slightly higher than before. Shortly after the photo, I climbed a fairly long and steep hill in 3rd and the temp climbed. And then had unplanned detour and stop and go. Always stayed in the green bar. It’s definitely running cooler with no t/stats.
 

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Re: Temperature experiment- ‘46 Mercury

I use a modern t/stat in my 33 &34, tig welded to a short ss tube and pushed into the top hose
Lawrie
 
Re: Temperature experiment- ‘46 Mercury

You didn't mention if you are using an original temp sender or repro unit. I've been dealing with a temp gauge that tends to read on the high side. I have a new repro sending unit from Third Gen. After getting up to temperature on a hot day, I have checked the coolant with an analog temp gauge with a probe placed directly into the coolant and it reads 175-185 consistently. I get the same reading with my Klein IR thermometer, aiming at the center of the cylinder head. My assumption is that the sender is not necessarily accurate perhaps due to a calibration issue. Bottom line is, even though the gauge reads on the hot side, measurements don't seem to indicate overheating and it is not spitting coolant out the overflow tube.
 
Re: Temperature experiment- ‘46 Mercury

I have removed the stats on a number of my vehicles. Each of those then ran significantly cooler when measured under the same conditions at the same places.
 
Re: Temperature experiment- ‘46 Mercury

Curious if you are using water or antifreeze. Engines using antifreeze tend to have a higher running temperature of an engine using plain water.

Also curious if have you recently cleaned out the radiator and the block?

I also agree with Lawrie on the T-stats. I use Stant super stats for a Subaru Justy and have had excellent results.

mcgarrett also brings up a great point and would be interested to see if you could take a manual reading of the coolant in the rad to get a baseline of what the gauge is reading.
 
Re: Temperature experiment- ‘46 Mercury

Bruce_MO said:
I took the challenge… it’s sunny and 86 degrees now. Photo shows steady state at 32-35 mph on a level road after a few miles to reach temp. It’s slightly higher than before. Shortly after the photo, I climbed a fairly long and steep hill in 3rd and the temp climbed. And then had unplanned detour and stop and go. Always stayed in the green bar. It’s definitely running cooler with no t/stats.
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573384
 
Re: Temperature experiment- ‘46 Mercury

Radiator is a new core, temp senders both originals, running approx 50% antifreeze. When it was just beyond the green area on the gauge, the top tank was reading around 195-198. I’ve been taking many readings of temps on the heads and radiator with my infrared gun, and the heads’ surface temps are hotter than the coolant… maybe 200-205 when the coolant is 180 in the top tank. It is definitely running cooler now, with the thermostats removed. I have a ‘53 that seemed to run hot, and I changed the (indicating) sender with a different original, and the gauge started reading maybe 1/8” lower. I know they are imprecise, but they’re definitely capable of telling you you’re getting hotter
 
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