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1977 F-150 with early 429. Truck runs very hot at times when on the highway, and in the city, too.

The motor is not fancy; D0VE heads, mild cam, iron intake, AFB, and exhaust manifolds. I guess about 9.5-9.8 CR or so, so not enough to raise eyebrows. Runs fine on regular gas but likes mid grade to high octane better.

It runs pretty cool for a while, then all of a sudden, the temperature gauge goes almost all the way to the right. Not sure it would go the rest of the way because I turn it off before it goes the last little bit.

It has a new Standard sending unit, so it could be bad, but maybe not the first thing I would check.

It had a 195* thermostat and did the same thing on a 300+ mile trip to central Florida in June. After I got back I changed to a 180* Milodon and it ran much cooler until it almost pegged yesterday on a 106 mile round trip.

With the first thermostat it would run at the normal temperature for a couple to three hours, then overheat. After that, only a half hour to an hour, then get very hot. Seemed to get hot after a stretch on the highway and then when I stopped at the first red light it would overheat right away. I'd pull over, turn it off for a minute or two, then crank it right back up. The gauge would be back at normal within a couple blocks. Thing is, it would not get hot slowly, creeping up a little at a time. It would be fine, then you could watch the gauge rise until I ran out of nerve. Usually it would get hot before a red light could change, or when it decided to get hot on the highway, within a mile or two on the open road.

I doubt the cooling system is not up to the job because it cools down so quickly. I doubt a bad gasket or a cracked head because the water level has not dropped.

I don't mean to eliminate things with this doubt stuff, I'm just giving my reasoning hoping someone will tell me why I am wrong about this.

I thought the first thermostat had a weak spring and after a while being in the hot water, the valve just gave up and closed. So I went to the 180 and all was better for a couple months until yesterday.

I have an IR temperature gun. Other than the obvious hot/cold areas in the radiator, is there a particular place I can point it at on the engine that might help narrow this down?

This has me stumped. There is always the buy and try method of diagnosis, but if someone can point me to a specific thing I'd appreciate it.

Thanks, Y'all.
 

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I'll assume you are looking at stock gauges. My 72 did the same thing at times. Can't trust the instrumentation.
Yes use IR thermometer and see what temp of intake at coolant sensor is.

The temp rating on thermostat should not have any impact on 'overheating' it will just open sooner or later.

If carb is lean it will run hot under load (highway). What is AFR at idle and cruze?
 

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I agree with the comment about the factory gauges sometime doing something funky. Try to check it with the IR gauge. Does the factory gauge ever go above the "normal" portion of the gauge? The part about it running relatively cool for some time and then suddenly getting overheated seems strange. Something must be changing to make this happen, be it in the gauge or in the cooling system. I'm assuming that all the other gauges are acting normally. While it's hot check the area around the thermostat housing with the IR tester.
 

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The other posts are great help, and I can only add just a little. Yes you need to look carefully at the plugs, and other indicator of running lean,white colored inside of exh manifolds, high exh manifold temp/cracking. Ignition timing at 2200 rpm. If nothing jumps out there, take the rig for a short ride. When you pull into the driveway quickly get to shooting your IR temp gun and take readings at top tank,bottom tank,and carefully at every height of radiator that you can. All this to look for a flow problem or poor heat transfer in the cooling system. Remember that the very center of the radiator has poor airflow and can lead you a stray. The guage could indeed be the problem, but you are right to not trust that all is still at operating temperature. It is very possible that minor cooling problems exist, and finally overwhelm and quickly overheat.

Sent from my SM-A505U using Tapatalk
 

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Discussion Starter #5
Good ideas, thank you both.

I've been driving since about 1964 or so and have had gauges completely quit, but never go this haywire, so I never would have even considered that one.

It might take a while to diagnose this one because it does not overheat on short trips; only once it has been running for 45-50 miles or more. That is not on the schedule soon, but it might happen.

When I got the truck the temperature gauge did not work at all. No apparent problems such as steam from the radiator cap or running low on water. Then I bought the sender and it started working, so I figured the electricals were OK.

I'm supposed to go to a nearby city next week on business if I get lucky and can get off that day. I'll be ready for it this time.
 

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You might want to check the wire going from the gauge to the sensor. It could be shorting out when it moves a little and giving you a false reading.
Greg
 

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Discussion Starter #7
Been scarce lately; my job has -really- clipped my wings.

All this sounds good to me. Reading between the lines, it seems that overheating is not the problem, wiring is. I hate wiring because it takes three weeks to find and three minutes to fix. The fixing part is OK, the finding part will make you say something your mama would not approve of.

I thought it was peculiar that when I shut it off and cranked it up, no signs of overheating were present: dieseling, knocking, hard starting, the usual stuff you would expect to see.

Will try to take a look at in the next week or so, and will report back so this might help someone else.
 

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The gauge cluster has a regulator on the back. That is for the gauges it's suppose to supply 5 v but they will act very erratic just like what is happening to you. I have a 79 ranchero that does the same thing. make a mental note of your gauge locations next time you go for a ride. Now when you notice the temp gauge rising see if your fuel and oil pressure gauge are doing the same. if so it is that regulator and not your engine. you can buy a solid state unit and that should in most cases fix your problem.
 

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my 2 cent from experience but, could be the radiator, my application is different but the principals and theory is the same, I have a 545 blown fuel injected did the same thing would run about 2 cycles of the thermostat opening and closing then over heat, I would shut it off run the electric fan and electric water pump and it would cool right off, I checked and changed all of the following,

head gasket orientation,, they were good
intake gasket leaks - no leaks
exhaust gas temp gas 485 f +/- 10 degree between cylinders
ran 3 diff stats
ran 3 diff restrictors
ran ign timing from 10 to 40 adv
used 2 diff gauges
used 2 dif senders
i borescope the pump/block/cyl heads
used 3 diff radiators /be cool/ frost bite/ northern
used 2 hyden fans / 2 perma cool fans/ and a taurus fan
used staight water/straight anti freeze / used 50/50 anti freeze
use 4 different sets of spark plugs
IT STILL OVER HEATED lol

i spoke to don hampton/ dave at bad *** racing engines/be cool/ summit/jegs/ no one had a answer, other than 1 older much wiser gentleman over at afco radiators, he explained in grave detail the theory of the BTU, after a while some radiators become clogged or even pitting and distortion in the cooling tubes, and bent fins or just dirty fins, the coefficient of the radiators ability to cool is reduced to a point where it cant remove enough of the heat or BTU, and it will keep building until it over heats, and in my case it was the radiators I was using wasn't efficient enough I had to come up with a way to keep a 1/4 mile race engine to run cool on the street not just 1/4 mile at a time, he told me if buy his stuff he is going to recommend it would fix my problem and if not he would refund me for the parts, at this point i had spent over 2k in cooling system crap, hesitant as i was i spent $485.00 and it fixed my problem i run 190 -202 on 90 degree day in a full size 2 door big tire 545 871 blown car with a 4000 stall and 430 gears it was the radiator he sold me a dual pass radiator 1 bottle of there coolant additive and there radiator cap and a 190 stat...

flush your radiator take it out clean it really well comb the fins back flush the fins rent a borescope check for sediment build up in the tanks and tube openings put it back in see if it gets better if so buy a radiator or after you inspect it and you feel there are issues there just replace it.
 
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