Why is my 74 running so HOT 230 degrees+!!!

[BajaFresh75]

I have a 74 that is running extremely hot. The gauge is reading over 230 degrees. I have a laser thermometer and all the readings on the water neck, hoses, radiator, intake, sending unit all read 135-175 degrees. Here's a list of what I've done. Some of this I was doing any way.

1. new 4 core radiator
2. new heater control valve
3. new heater core and blower motor
4. new sending unit
5. hooked up another temp gauge from another EB cluster (same reading 230 degrees).

Any ideas? The water pump is not that old, and FYI I'm not sure if it has a thermostat, I'm assuming it does. The Bronco runs and drives fine and doesn't overheat, but I hate looking at that gauge and seeing 230 degrees!!! I thought about running a new wire from the gauge to the sending unit. Any ideas welcome!!!

 

[broncnaz]

replace the sending unit or at least make sure it doesnt have teflon tape on it also clean the connection. Since you've checked readings with a laser guage then that kinda rules out everything except the sending unit even new ones can be bad or just the wrong one for your guage
.

 

[00gyrhed]

i say this everytime you are not overheating until you boil out water. As long as liquid water is being circulated you are not overheating. The laser might be right but I have seen new lasers off by 1-5 degrees right out of the box new. this is a part of my bussiness. Even expensive control sensors can be off 10 degrees right from the factory.

Take out the sensor. Wrap a good ground around it. Drop it in boiling water. Ask your mommy at what temperature water boils at you elevation. I say that because most of them know if they ever make candy, heck they might even have an accurate thermometer. To test a thermometer. Put it in boiling water and see what it reads. Also put it in a slurry of ice and water give the ice time to warm up and the water to cool down. When measured it should read 32 deg F.

When you test the gauge it should read the boiling point of water at your elevation exactly, other wise the sensor and or the gauge are wrong. NOT BAD JUST WRONG. Remember how far off and just make the adjustment in you head, or you can bend the indicator. That is called calibrating the gauge. These gauges in these old vehicles are never accurate. A lot of people make expensive decisions based on a device that was really only meant to show changes and not exact conditions.

 

[fatboy4211]

i put a 4 core radiator in my 74 (302 auto) along with a 180 thermostat. new stock water pump, new hoses and stock shroud. mine reads 190 most of the time and 210 with the ac.
when it was in the 20s (superbowl week) i covered the air intake with the highly fashionable cardboard and barely got it to cross over 180. then the day came when 60 was the norm again. i was going down the highway when i remembered the cardboard. it was pegged out at about 200.
are you using a shroud? stand in front of my grill and you can feel the suction from the fan.
is the fan clutch operable? not sure why but i once have one go out on a different vehicle...and it was the culprit.
the other thing that crosses my mind is if the water jackets are hindered by obstructions such as rust buildup
im no mechanic, but i have crossed that road before. me and my wallet took a beating

 

[Broncobowsher]

So far we have that you are using a stock gauge and a mystery sender and you think it is running hot.

Still need confirmation that it is running hot. All we know right now is that 2 different gauges read the same. No idea if the sender is sending accurate info, bad ground can make a voltage differential that can affect gauge readings as well.

Try a harbor freight cheapie gauge calibrated in the kitchen in a pot of boiling water (make sure the sender is in the water and NOT touching the sides of the pot).



Rareley will an engine come up to 230 and just sit there. If it is getting that hot the temperture will swing all over the place with slight changes to idle speed and load. If it is hitting the thermostat the temperture will be pretty stable, what ever it is. Still not convinced you have a cooling issue as much as a gauge issue.

 

[Rustytruck]

with the engine cold remove the radiator cap, Is the radiator full to the top? its supposed to be.

Start the engine if the water is rushing around right away the thermostat is not there or stuck open.

Put a thermometer in the coolant and read the thermometer does it match the guage. Does the water tempperature rise on both guages the same. Is the temperature close like 5 to 10 degrees or so? should be slightly lower at the radiator.

Do you have an overflow bottle with coolant in it? There is supposed to be one.

Use a new radiator cap I recomend 15-16 lb without lever release.

The wire for the water sensor is actually a ground wire. the guage gets ground through the sensor to the guage. The sensor which is really a variable resistor. Eithor the sensor is bad or the guage is off calibration if it is reading false. The sensor must be installed without any type of sealant. Bare metal to bare metal. If you disconnect the guage wire at the sensor with the key on and ground the connector to the block the guage should go hot to the top full scale. If you disconnect the wire and do not ground it is should go full cold to the bottom of the scale.

Many moons ago my 1974 had strange overheating problems and was running hot but didn't boil over. If I stopped for gas and shut off the engine it would boil over about 5 minutes after I shut it off. It took a while to find the problem. In the end it was the origional head gaskits they were leaking combustion gas through the gaskit to the waterjacket. When the engine was warmed the hot gasses went through the gaskit and raised the water temperature. When I shut off the engine the cylinders under pressure leaked through the gaskit and over pressured the radiator cap and pushed coolant with it. It seemed like it was overheating but it wasn't it was combustion pressure. After removing the heads I found the fire rings in the old gaskits from 1974 were plain steel and rusted through leaking pressure through the fibers of the gaskits simulating the overheated issue. After replacing the gaskits I was good to go. Sometimes what you see is not what is really happening and you have to think outside the box.

 

[Viperwolf1]

A bad ground at the sender will make the gauge read low. A bad ground at the IVR will make the gauge read high.

 

[allenfahey]

I start by making sure you have a t-stat. I'd pick up a new 190-195 t-stat while you have the housing off. I'd also use a fan shroud if you don't have one.

 

[BajaFresh75]

You guys really know your stuff. I have some work to do. The old sending unit had teflon tape and the new one has teflon tape. That's where I'll start tomorrow. Thanks!

 

[Steve83]

The IR thermometer says you're not running hot (not really even fully warmed up), and you're FAR from overheating.