I currently have stock thermostats in my F1, I think they are 180 degree. They are both working OK, but it seems like it takes longer to warm up than it should.

I guess what I mean is the motor seems to run best without any choke, long before the stats open. So I was going to experiment with 160 degree stats, to see what that does.

Do I have to drain all of the coolant when I take the stats off, or can I get away with just reducing the coolant below the level of the thermostat housings on the block.

I do understand that putting 160 deg stats in is not going to lower the peak temperature which is around 180 to 185. But the 160 degree stats should let the truck warm up to operating temperature a little sooner.

Thanks for any input.

 

Colder thermostats will not help the truck reach operating temperature faster. All that will change is the water will start circulating earlier when the stats open at 160 rather than 180, which may have just the opposite effect of what you're looking for. It's no different than the thermostat for your furnace in your house. Setting the temp at 80 won't bring your house up to 70 any faster than if you just set it at 70, contrary to popular belief.

 

Stick with 180's. When the system settles down, they usually run around
178-170*. at least mine does. Odd enough one of my two warms up
faster then the other, I got no clue why. My salt sander takes for
ever to get to normal (180 degrees 8BA)

 

I had a couple of new 180 degree Stant brand thermostats that were in my parts box. Out of curiosity, I put one of them in a pan of water on my induction cooker where I can set the temp very accurately. I set the water temp to 180 degrees, let it stabilize, and checked the temp of the thermostat itself with an IR gun that I know is ccurate, and it was 180. The thermostat had just begun to open a crack. So I inceased the water temp to 190, checked again after it stablilized, and the stat opened a little more. It took a little over 210 degrees to open fully and stay open. I dropped it back to 190 and it started to close.

So what that tells me is these are designed to open gradually, not instantaneously, and there may be manufacturing variations in their published ratings. A 180 degree stat may not be necessarily open fully at 180. My truck will warm up to around 200 degrees, and I can tell as soon as the thermostats open by holding the upper radiator tubes. Then the temp gets a little higher and begins to drop back to 185 where it stabilizes (with 180 degree stats).

What I am trying to do with the 160 degree thermostats is to prevent that "overshoot" of temperature, so the temp will be around 180 when the thermostats are all the way open, then it will drop back to normal temps and stay there.

These are not precision devices. I have seen many posts by people who consider themselves "expert mechanics" that swear by 160 degree tstats only in a flathead. I have seen other posts by people who swear that 160 degree thermostats will lead to misture and sludge buildup / serious engine damage.

I am going to try them to see what happens. I can always go back to 180 if I don't get good results.

 

Just spitballing here, there's no flow nor pressure in a pan of water. Maybe a thermostat will open farther in use at a given opening temperature? Interesting observations in any case.

 

Ok so I did the hot water test of two brand new 160 degree thermostats made by Murray, again in a pan of hot water with my IR gun pointing at the end of the copper "piston" which was sligtly out of the water. Here's what I got (and both are performing within 2 degrees of each other).

160 Degree Murray thermostats are approximately 50% open at 160 degrees, fully open at 170 degrees, and fully closed at 150 degrees. So for my application, they will start to open sooner than the 180 degree thermostats that I now have in the truck (which take almost 200 degrees to open fully), and should eliminate the 220 (approximate) overshoot that takes place before my engine temp starts to drop back to noprmal at 185 degrees.

I really doubt that water pressure in the system would change the opening points, especially considering the "beefy" springs on the theremostats that must be overcome by the "piston" that reacts to the temperature, and the less than "beefy" water pumps in an 8BA flathead.

I will be happy to post the results after I get the new thermostats installed. All motors are different, even identical 8BA flatheads.

My (recently rebuilt) 8BA seems to he happiest based on smoothness of idle and sound, when it's up to anout 180 degrees with choke fully open. If it is really cold it takes a little choke to start it, but too much will flood it.



It's a great truck, and I am really enjoying it. Just got some personalized coffee mugs made:

 

The temp stamped on the thermostats is supposed to be the opening temp (cracking open). If the 160's are half open at 160, your engine will run too cool.

From the choke performance you describe, I'd say you are running rich. Turn in the idle mix screws until you hear some stumble, then out as little as you can to smooth it. The screws affect mid-range and cruise more than you'd believe. Rich engines run cool and wear out fast.

 

Hi ross,

Now I'm curious. Why would the "idle mixture screws" since they are in the "idle circuit" affect mid range / running mixture. I suppose there is a little overlap between the idle circuit and the main jets, but you say "significantly affect" mixture above idle rpm. Can you help me with that?

I did adjust the idle mixture screws for the peak idle RPM, then lowered the idle RPM back to where the specs say it should be. The truck starts instantly, runs smoothly at all speeds, and I no longer have the "off idle stumble" that I had before. I will try what you suggeted to see, but my plugs are not indicating rich running, they are light tan in color, not black, and very clean looking.

 

Hi ross,

Now I'm curious. Why would the "idle mixture screws" since they are in the "idle circuit" affect mid range / running mixture. I suppose there is a little overlap between the idle circuit and the main jets, but you say "significantly affect" mixture above idle rpm. Can you help me with that?

I did adjust the idle mixture screws for the peak idle RPM, then lowered the idle RPM back to where the specs say it should be. The truck starts instantly, runs smoothly at all speeds, and I no longer have the "off idle stumble" that I had before. I will try what you suggeted to see, but my plugs are not indicating rich running, they are light tan in color, not black, and very clean looking.

 

Ok, so call me stubborn, but I have to try things out to learn what I am doing. I did put the 160 degree thermostats in today. I was a little surprised at the results.

WIth the 180 degree stats that were in the truck, under normal running conditions, it would climb to about 200 degrees, the when the stats were fully open, the temps backed down to 185 to 190. I never really had an overheating problem except once when I drove in a Veterans Day parade for about one hour, and it got really hot so I had to bail ut of the lineup.

So now, it climbs to about 175, the stats open and it seems to maintan 175 under all normal runing conditions, Before with 180 degree stats, the gauge on the dash ran almost all the way to H then backed down to just under halfway between center and H.

Now with the 160 degree stats, the gauge shows just over the center position, and stays there (no more overshooting). I drove it all around my community (not interstate speeds but 40-50 mph), and it never went higher that 175 degrees.

What surprises me is that everything I have read (on this forum), says that lower rated thermostats will not lower the peak temperature of the motor, it just starts cooling a little sooner. I have found that to be incorrect (at least for my truck). I have lowered the running temperature from around 185 to about 170 by changing the thermostats. I do think it seems a little richer now, so I need to adjust the carb to fix that.

So if you think you might have an overheating problem (and with flatheads who doesn't?), you might want to try 160 degree thermostats. It only takes an hour to do (except for the first time : - ). Try it, you'll like it.

 

Thank you for your testing and observations!

 

I would say your statement is not entirely correct, unless you've only been selectively reading. I know I've never said using colder thermostats will not lower the "peak temperature" of an engine. There are a lot of factors that play into what temp an engine will settle in at, including cooling system capacity and condition. If you got the desired results from your swap, that's great. But a thermostat's job is to regulate a correct operating temperature. For most engines, that is in the 180-190F range, flatheads included. Running colder 'stats is not a cure all for higher operating temperatures. As noted here, if you have a weak water pump, clogged radiator or rusty block creating an overheating issue, a different thermostat will not cure those issues.

Based on your comments and descriptions, ["My truck will warm up to around 200 degrees, and I can tell as soon as the thermostats open by holding the upper radiator tubes. Then the temp gets a little higher and begins to drop back to 185 where it stabilizes (with 180 degree stats)."] you didn't have a problem with your engine, it was working as designed and efficiently. You simply thought it should operate differently then created a scenario in which it would. Congratulations.

 

Thermostats are designed to assist in getting the engine up to operating temp faster. As Wayne said if working properly they do not control normal operating temp. The radiator, water pump speeds (flow) and air flow (fan in parades) impact that. Timing and carb mixture also contribute more or less depending upon the engine speed and load. You might want to check the carb power valve. If you have had a backfire in the engine as it can cause that valve to leak. IMHO a 160 degree thermostat is too low and will cause plug fouling and other problems as Ross indicated in his post. Particularly if the engine isn't run at highway speeds often.

 

Thanks everyone for your comments. My flathead has been totally rebuilt just before I bought it (less than 5K miles back). The block was boiled out and cleaned thoroughly. It has two new water pumps, and the radiator looks really clean also. I did have a leaking power valve problem which I reorted on earlier, that has been resolved (the carb rebuilder left the gasket off the PV). The fan is a 5 blade fan. The ignition has been upgrded to a Pertronix retrofit with a "Flame Thrower" coil.

I know there are a lot of factors regarding engine temps on flatheads. Overheating is a topic near and dear to all of us. The good thing with my 160 degree thermostat experiment is that if running at 180 engine temp is too cold at highway peeds, and I can't get it leaned out to my satisfaction, I can always go back to the 180 stats that I had and run it hotter, so it's not a permanent decision. Actually I have gotten pretty good at changing them out. I read comments recently on another website / forum that said "we never run anything hotter than 160 degree thermostats in our flatheads" - period!

Please understand that I am not trying to challenge anything that anyone writes on this forum. What really matters is what works best for each of us, and the advice I have gotten here has been invaluable to me. I am not an experienced mechanic, just trying to learn. But I do like to try different things that make sense to me, before I accept anything as gospel.

Cheers.

 

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