The Stovebolt Site Forums The Shop Area Engine Shop overheating, but maybe not...

I have just restarted my 56 (235 6-cyl) after a 2-year rest while did a frame-off restoration. it will need to be fine tuned, but for right now it starts up readily and idles nicely. I think it might be getting too hot though. the radiator is new, as is the thermostat (180 deg) and all of the hoses. the cooling system - except for the water pump - has all been replaced. After about 10 minutes, the temp gauge starts to climb toward "H" and eventually pins the needle there. I shut down the motor then. The upper hose was hot at this point, as was the top tank of the radiator. He bottom hose and bottom tank were quite cool. I then changed the temp sender (i have the electrical gauge/sender system) to eliminate that variable, but the same thing happened again after I restarted. I can think of a couple of possible areas where the problem may lie: 1) defective gauge, or 2) somehow the water pump isn't circulating the coolant either because it is bad or maybe its air-locked?; 3) blockage of some sort.

I also wonder if the engine is really overheating at all. Anyway - what ideas do you guys have as to possible problems or things to check? is there a way for me to take a reading (resistance or voltage) on the sender to calculate the temperature?

thanks for any advice.

Hot water into the radiator, cooler water out is how it's supposed to work. I'd use an infrared thermometer to see how hot the engine really is.

Maybe there is an air lock in the block?

ive had cooling problems at one time or another with all three of my trucks. when i replace a thermostat i first check it in a pot of water with a direct reading thermo, meter to see if it opens as its supposed to at the temp. its rated for. next i drill a 3/16ths hole in the thermostat which eliminates it from getting airlocked. since i have three new rebuilt engines they all got new water pumps and hoses. i then got all three radiators recored. since then i have had no more cooling issues in my trucks. my 40 runs warm when it's hot out and stopped in traffic. i have shot it with an infared camera after an hours run not long ago and when the temp gage was reading + 180 with a 170 thermostat the camera showed that the water was only 170 being discharged into the radiator. three quarters into my 630 mile run back from southbend it was running about 190 and i got concerned and pulled over and added some coolant, it only took about a quart and was relieved. it was hot that day and i was just about to crest the last ridge. after that the day started to cool down and it was down hill for a while which then it returned to what i call normal.

since yours is heating up so quickly is the thermostat installed correctly?

i believe the thermostat is in correctly (the pellet that is stamped "180" down into the housing towards the block and the opposite side under the gooseneck where the upper radiator goes). I did not test it first, but two different ones act exactly the same. i did drill a 1/8" hole in it. I think i'll have to get one of those infrared detectors because my whole issue here is that the temp gauge in my truck is telling me i am running hot, but there is no other indication. any tips on using one of these infrared readers - where to point it (head, block. etc) and what kind of numbers to expect with a 180 deg thermostat.

thx

stick a thermometer in the radiator while its running and see what the actual temp is coming from the block. it will read a little lower than actual but enough to get a handle on it. as for an infared i use a fluke. but any flaps should have what your looking for. they are good for checking temps. of other areas as well. shiny things dont do well because of the nature of the beast for that just put a piece of black tape on it to get a more accurate reading.

My 58 did that years ago. Turns out the gauge was bad. I put in two different sending units, thermostats, flushed the system. Finally installed a manual gauge to see if it was really getting hot, and it runs where it is supposed to.

I think you all are heading down the right path with checking the vitals with an external thermometer. However, one thing to look into if the readings are high is to check for plugged up passages.

This would require draining the coolant, and removing the petcock from the rear of the block. Removing it totally will allow you to pick around with a wire coat hanger or something. Sometimes the crud restricts things and wont allow the cooling system to do it job.

I had problems like that with my 54/235 and found that the sender in the new gauges was too short and reads block temp. rather than water because it is not in the water jacket. i put a radiator cap with a temp gauge on it to be sure. i got the cap at Auto zone but my local store does not carry them anymore. the dash gauge reads 20 degrees too high.

If your gauge is "pinned" and the rad cap is loose or off, it should be boiling over and producing steam.

well, that's good news. the gauge was indeed pinned and i had the cap off and here was no sign of steam. what i am doing now is calibrating the sender. i am heating it up and taking resistance readings. once i understand the R vs T curve, i'll run the motor and see what i get when the engine is warmed up - and i'll know the true temp. It looks like I can add a resistor to bring the gauge to where it belongs. I ordered one of those infrared temp meters to make sure everything is accurate. Now as to WHY i have to do this - i am not sure.

OK - I finished my science experiment and mapped out the resistance vs temp performance of the sending unit p/n 1233-4869. For those interested in the calculus, the best fit curve was:

R(T) = -230 + 25549 / T^0.81344

in words, this is the resistance (ohms) as a function of temp (deg F) is -230 plus the quantity "25,550 divided by the temperature raised to the power of 0.81344"

So next I will run the engine and take a resistance reading when it is warmed up. Hopefully it will be around 150 Ohm, indicating a temperature of about 180 degrees.

Sorry for the math, but I am an engineer...

Make sure your idle speed is not to low, my truck was over heating at idle also not enough air moving by to keep the engine cool. Just a guess????

Marv.

Charley, where do you get one of those thingamagigs?

Google Search

I use the one from Harbor Freight.

Where do you aim it, at the engine block?

Once you get your hands on it you'll be taking the temperature of everything in sight. But especially pay attention to the temperature at both ends of the head and the upper and lower radiator hoses.