360 Overheating

[olskool]

Have a mid 1970's 360 with 727 trans. This is in a 1948 Plymouth Coupe.
Trying to figure out why it's overheating. What's going on is it warms up fairly quickly when first starting and idling. Within 4-5 minutes the temp gauge is reading 200+ degrees. Kick it off high idle and it still does the same thing. Put the car in gear and take off and it cools down to 180 degrees within 30 seconds and holds it there while driving. Slow down to a stop sign or traffic light and it heats up. If you don't take off, it will overheat. Also, the radiator isn't as hot because it won't turn the electric fan on. The sensor is located in the bottom of the radiator and is to turn on if the water temp is 180 degrees. It never turns on because the radiator is cooler. I wired an on/off switch to ground the relay out and it turns the fan on and we leave it run when it's idling and even then it still starts to run hot. Take off, and it cools to 180 degrees. The radiator is a brand new aluminum radiator. The hoses are all new and there aren't any restrictions. I have replaced the thermostat 3 different times and no change, does the same thing. Water pump is brand new. Water isn't being pushed out through the radiator or reservoir. There isn't any coolant in the oil or vise versa. I verified the temp gauge with an infrared thermometer and it's correct with what the gauge is reading. Any ideas?

 

[Inertia]

Putting the sensor in the bottom hose senses the water after it's been cooled. I would put the sensor in the top hose so it can sense the temp of the heated water coming outta the motor.

You also need more fan/shroud/airflow thru the rad at standstill.

cheers

PS. Generally if you have room to run a OEM fan clutch, they seem to do the job better than most after market elec fans.

If you do a search on this site, you'll find a lotta folks having success using a Ferd Contour 2 spd elec fan if space is a problem.

 

[AJ/FormS]

Yeah,Inertia 'bout covered it.
Make sure your timing is not retarded, as well. See below.
If it overheats, parked, with the fans running,and
It cools as soon as you get moving.
Then,the fans can't keep up, they have to gooooooooooooooooooooooo

Or they are cavitating, or they cant push the air out from under the hood.
Are they pushing or pulling, not that at this point, it makes much difference.
Not to be an azz, but where did the idea come from to put the temp sensor in the coldest part of the circuit. Or rather the theoretically coldest part?
Shoot the rad with the IR gun. You will be looking for around a 30* difference from hot to cold;entry to exit, Keep the IR on the metal. If you are not getting close to it, it will be an airflow problem.

 

[RustyRatRod]

The sensor goes in the engine as stated. You know. Where the factory put it for like 75 years in millions of vehicles?

 

[72bluNblu]

Is this one of those slide in sensors that runs a thermostatic switch? They're pretty much the worst way to control an electric fan. they're not actually in contact with the coolant, which means you're already including the thermal conductivity coefficient of the radiator into your fan controller. Which means that switch will trigger at different coolant temperatures if the radiator is aluminum vs brass/copper. So it has to be calibrated to get the fans to fire at the right coolant temperature. Of course there's no way to do that other than moving it around the radiator to warmer or cooler spots. It's basically a guesstimate based switch.

And as already pointed out, the sensor is in the coolest part of the radiator, so it's not triggering the fan at the right temperature.

You need a controller capable of working off of a real temperature sending unit that sits in the coolant stream, preferably in the intake location the factory used. There's a reason they put it there.