Normal Temperature at 70mph +/- (1 Viewer)

[NCFarmboy]

Good evening! Wondering what type of water temperature you guys are seeing on a hot summer day, cruising between 65 and 72 mph?

Mine seems to hit 220F but stabilize and not go above; at 55-60 she runs 180-190F

Assuming this is ok, wanted to be sure;

1979 FJ40, 33’s w/ Stock 2F with Weber Carb

Thanks so much!

 

[1969FJ]

I believe you are within engine temp range. Seems summer outside temps, high end of engine operation would heat a bit more. As you do less speed/rpm ,temp goes down. Seems normal.

Your Engine's Cooling System · BlueStar Inspections

www.bluestar.com

 

[Skreddy]

Mines a 1970 with F engine and big ol 6 blade plastic fan, but I’m 178-182 regardless of outside air temp (as read on sniper display). Though we haven’t seen above 70 yet here. When we hit 70 the other day I was worried it was overheating because we were doing 70 mph and it hit 184….
I think 220 is fine. Is your thermostat, bypass hose, fan shroud, clutch/fan in good working order? System full and no air pocket?

 

[3_puppies]

these old rigs don't like that high a temp, I'm thinking it shouldn't get above 200
my other thought is there is an issue with that side of the cluster because you show over 15 volts which is also high

 

[Skreddy]

these old rigs don't like that high a temp, I'm thinking it shouldn't get above 200
my other thought is there is an issue with that side of the cluster because you show over 15 volts which is also high

Good catch @3_puppies. Now I’m wondering how you’re getting 74 mph at roughly 2200 rpm too!

 

[sogncab]

Good catch @3_puppies. Now I’m wondering how you’re getting 74 mph at roughly 2200 rpm too!

.85 gear ratio (I think that is a H55 over drive?)
3.73 ring and pinion
35" tires

2253rpm

Throw in a 5% error and you're there. Or I used the gearing calculator incorrectly, which is totally possible.

I'm just giving an example of how it could be there. I would guess the OP's speedo isn't spot on. He's running 33" tires as well, probably doesn't have an overdrive, and is probably running 4.10 gears. I was just curious what it took to get that speed and rpm combination.

 

[NCFarmboy]

I’m running 33x10.50 tires.

I’m assuming I have 3.70 gears being a ‘79

How could I verify the Dakota digital gauges being correct / incorrect?

 

[pb4ugo]

To get accurate speed download a good GPS speedo to your phone. Your tach is probably pretty close. You can double check it with a multifunction timing light.

 

[Skreddy]

I’m running 33x10.50 tires.

I’m assuming I have 3.70 gears being a ‘79

How could I verify the Dakota digital gauges being correct / incorrect?

Do you have a 4 speed or 5 speed?

As @sogncab showed the math, I think a 5 speed is the only way to get that rpm/speed.

 

[sogncab]

How could I verify the Dakota digital gauges being correct / incorrect?

There is an option where you can set the speed, and once you are moving at that speed, you basically sync it. You do it from the Dakota Digital application on your phone. Mine is really close doing it that way, but it did take a couple of tries to make me happy.

I doubt the tachometer is off enough to care.

The faster you are going the more accurate that synching will be.

 

[NCFarmboy]

Wow! Didn’t know there was an app for my phone…

I have the factory 4 speed transmission

 

[sogncab]

Wow! Didn’t know there was an app for my phone…

I have the factory 4 speed transmission

Interesting.

2200rpm
3.73
33" tires.


73mph.


Or, I did the calculator wrong....

 

[sogncab]

I did do the calculator wrong. That says 5th gear. Hold on....

 

[pb4ugo]

Your gauges are off. At 74mph with a 4 speed, 3.70 gears and your tire size should be running around 2800+ rpm.

33" tires are probably closer to 32". You should measure them to be accurate.

 

[sogncab]

There. This feels more correct.

 

[pb4ugo]

There. This feels more correct.

View attachment 3038941

His Stk gear ratio is 3.70:1.

 

[sogncab]

His Stk gear ratio is 3.70:1.

Three hundredths didn't change it enough to show a different number. Still shows 58mph.

 

[RockDoc]

Tach set for 8 cylinders rather than 6?

 

[sogncab]

Tach set for 8 cylinders rather than 6?

Would that put him at close to 3k rpm?

(2200/6)*8=2933

 

[3_puppies]

are we sure it is 3:70's early 1979's still had 4:10's so it matters what month the 79 was built in

this still doesn't help his running hot issue