How hot is too hot?
 

So, I've got less than 500 miles on my freshly rebuilt 59A-B flathead. .040 over, Merc 4" stroke crank, Isky Max-1, dual Stromberg 97s w/.041 jets, 180 thermostats, shrouded electric fan with 185 switch, 4# cap, dipped radiator. Before yesterday, it had been staying around that 185 mark, even in hot weather at highway speeds (65 MPH/1,580 RPM). Yesterday though, it was about 90 and I was cruising along at 70 or so and 1,680-1,700 RPM and it started to get hot . . . 206-207. I pulled off the highway, and it immediately dropped down. I got back on the highway, and cruised at about 65, and it went back to the 185 range. My question is, should I be concerned at 206-207? If not, what's the temp I should be concerned at?

Re: How hot is too hot?
 

I had a similar problem in an O/T engine I had rebuilt. The engine would overheat any time I let it sit and idle for any period of time. I was just getting ready to pull it and tear it down, but after about 800 miles, the problem went away. I can only figure the engine was built "tight", and with enough miles loosened up. Since your engine only overheats sporadically (and 206-207 ain't that hot), I'd give it a few more miles. The '51 Mercury in my '51 Ford runs consistently at about 180 (the thermostats) just about all the time. However, extended periods on the interstate at 70 and over pushes the temperature to 190.

Re: How hot is too hot?
 

As long as it's not boiling over you should be ok.

Re: How hot is too hot?
 

Heating problems aside and out of curiosity, just what transmission, differential and tire combination are you using to achieve (65 MPH/1,580 RPM)?

Re: How hot is too hot?
 

Trying to help. Water at sea level boils at 212, add 4 pounds of pressure, and at 3 degrees increase of boiling point for each pound of pressure, you get boil at 224. Eyhylene Glycol 50/50 changes these numbers up a little bit. Boiling makes pockets where there is no water contact with the metal among other issues.

I roll as JSeery suggests, if coolant is not coming out, it's not too hot. But I run much more stock stuff that the OP's rig.

Re: How hot is too hot?
 

Short answer= 230° is too hot.
If you are cruising at 65 mph and can't stay below 210° something is wrong with your heat exchange. Most old cars have the opposite problem. Good temps at speed and heat up when stopped.

Re: How hot is too hot?
 

Sounds off by 1000 rpm for normal gearing and tire diameter.
And .091 jets in a 97 carb is way rich. Something off there too.

Re: How hot is too hot?
 

What kind of capacity are you running as far as water volume?


My engine with Mitchell a 36z5 over od does at least 2 plus k at 70. cruising rpm.

Re: How hot is too hot?
 

T-5 trans., 2.73-geared Ford 8.8, 235/65R16 tires. Thinking I may need to change to a 3.08 to get it more in the engine's power band on the highway.

Re: How hot is too hot?
 

Typo on jet size. Should have said .041.

Re: How hot is too hot?
 

Thanks for all the replies. I'll just keep an eye on it. Trying to keep the RPMs varied as I break in the motor.

Re: How hot is too hot?
 

Sounds like a great and much coveted setup. The 3.08 should kick up the RPM by a few hundred.

Re: How hot is too hot?
 

Some .043's or .044's would absolutely cool it down.

Re: How hot is too hot?
 

I agree with Uncle Max - you are probably too lean on the jets - try .043 to .045s.

Also, you are correct on the rear-end ratio issue - you are nowhere near the RPM that you need to be - not enough torque to pull your final gear ratio.

Do your calculations (tire size, OD ratio, etc) - and get to at least 2200 RPM at 70 . . . I'd go a bit more 2300 - 2400. Right now, you're lugging the engine - which also isn't good for temperatures or anything else.

Re: How hot is too hot?
 

i'm running about 2300 rpm at 70 mph. Get around 20 mpg on the highway.

Re: How hot is too hot?
 

Assuming 27" rear tires, the RPM calculator says that Ritzy1 should be turning about 2378rpm at 70 in 4th gear (1:1 ratio). That would be an option to check the operation and temperature at normal RPMs.

Re: How hot is too hot?
 

70 at 1700 rpm. What rear end do you have? Overdrive?

Re: How hot is too hot?
 

See post #9 above--
"T-5 trans., 2.73-geared Ford 8.8, 235/65R16 tires."

Re: How hot is too hot?
 

So the motor is loaded up and lugging?

Re: How hot is too hot?
 

I have been fighting overheat at interstate speeds. Have 3 97's on progressive, all with .045 jets. Went to .048 on the center carb and that dropped cruise temp by about 10 degrees. At that speed, the secondaries are open, so they are getting .048 jets as well.

Re: How hot is too hot?
 

Thanks again for all the feedback. As many of you know, these carbs come with .045 jets. Since I'm a rookie with flatheads, I consumed Vern Tardel's book How to Rebuild and Modify Ford Flathead V-8 Engines. That became my bible. In there, he recommended starting with .041 jets with a dual carb setup at sea level, which is what I did. When I first started it up, it went way hot, so I changed back to the .045 jets. After some tuning by John Freeman at Freeman's Garage (authorized Stromberg distributor), we decided to put the .041s back in. There may indeed be a happy medium (.043). Again, it's only been on the road for two weeks, so I'm still sorting. I do love how it cruises along effortlessly on a flat highway at low RPM in 5th, but I realize I've got to raise the RPM up for when I come to a hill. So far, I've just been dropping it down a gear if it starts to lug. I think I've yet to get it above 3,500 RPM in any gear.


40cpe, I'll test your equation when I take it for a spin later this week, and let you know the result.

Re: How hot is too hot?
 

I have no overheating problem cus I just got the engine fired up. But in a 32 Roadster with 281cu in 59AB and 3.27 rear end gears I calculate 2700 RPM at 70. Is that to many RPMs. Tires are 28 1/2 diameter

Re: How hot is too hot?
 

Just depends on the rpm range you are comfortable with. I like to keep the engine in a bit higher rpm range myself, other do not. It also depends on the cam you are running. I like a longer duration higher lift cam, there for the higher rpm range.

Re: How hot is too hot?
 

Thats why Model Ts have no temp gauge !!! LOL

Re: How hot is too hot?
 

I don't think it's too hot, YET! like tosee cruise RPM around 2400 with a Max#1 cam. Enjoy the ride.

Re: How hot is too hot?
 

Running that trans./rear end gearing you may be lugging. I'm running the same overdrive trans. with 3.25 gearing and 235/70/15 tires and at 65ish in 5th gear i'm at about 1900 +- rpm and I almost feel 3.40 gears are possibly more suited. With your gearing you may consider running in 4th gear. I am running the V8 Camaro 5 speed that has the 2.95 first gear so you may have to consider your first gear ratio for your decisions. As far as a final rpm probably 2100 to 2500 rpm is a good safe range. Some folks may dis agree.

Re: How hot is too hot?
 

Interesting to see you recommending 2,400, Ron. Putting this thing together, my mind was thinking low RPM at highway speeds like a modern car (1,800-2,200).

I was also surprised to see flatjack9 getting 20 MPG running 2,300 RPM.

This is how I learn. Great resources here! Thank you!

Tomorrow night when I get home I'll see what the RPM is in 4th @ 70 MPH.

Re: How hot is too hot?
 

I also think the water pumps have allot to do with the temp. along with the radiator and condition of the block water jackets. Most modern radiators have a 7 LB cap. Yet some engines overheat. Flatheads do that????

Re: How hot is too hot?
 

Just to keep this in this thread and not start another.


rpms.


Idle about 1000-1200
Running/cruising 2000 -2400
Max on a hop up 3,500-4,000


???


.

Re: How hot is too hot?
 

Do not pay attention until it starts to boil.

Re: How hot is too hot?
 

This seems high. What cam are you running?

Re: How hot is too hot?
 

I like a fast idle, but that's way beyond a fast idle! Your halfway through the advance curve.

Re: How hot is too hot?
 

I idle at 800 with my 39. I like the speed up a little because of the cam and the crank mounted fan.

Re: How hot is too hot?
 

Mine seems to idle all over the place. It certainly doesn't like to idle when it's cold. If I try to hit the road too fast, it'll die when I come to a stop. Once it's warmed up it can range from 750-900. I need to check to make sure the throttle's not sticking somewhere.

Re: How hot is too hot?
 

Is your temperature gauge accurate? You can boil a pot of water at sea level and it will be 212 degrees.

Charlie Stephens

Re: How hot is too hot?
 

Haven't tested it Charlie, but I also don't feel the need to. It's brand new Dakota Digital stuff, and when the fan kicks on using a separate thermostat control, the gauge is reading 185.

Re: How hot is too hot?
 

Yup, 2,380 RPM @ 70 MPH in 4th. Right on. It did tick up to 205 on both heads again, but dropped fairly quickly when I slowed a bit. May need to fatten it up.

Re: How hot is too hot?
 

What is your rear end ratio

Re: How hot is too hot?
 

I probably idle at about 600-700, I'm guessing... Don't have a rpm on the car but have a rpm tester, never really tested, just by ear (guess I'll test it, i tune with vacuum). I do have a reground cam, it's a bit lumpy. Could use a bit more idle so it doesn't load up idling. I do run a vacuum gauge in my 36 full time, no rpm.


It was just a topic suggestion I made for discussion. Not what I run.

Re: How hot is too hot?
 

Have you put a vacuum gauge on the car? How are the plug reads? Sounds to be too lean from that description. Possible float or fuel pressure. Just from your post above.