Overheating, at my wits end (long)

[crustysarge]

OK, 72 C/10 with stock 350. Like a dummy I decided to change the antifreeze thought it looked decent. Radiator had some calcium deposits so I decided to flush. Used Prestone crap and then used some diluted muratic acid. Cleaned it fairly well.

New antifreeze after clean flushing several times and getting out old water by blowing on heater hoses too.

Drove for two weeks just around the house/work which is less than a mile. No problems, really not enough to get warm. Went on a 60 mile trip and after a few miles noticed temp gauge was at the start of the solid line on the right. Ran heater to help cool until I got to my buddy's shop. Never got hot to where it boiled over and needle never went into the solid line area. Yanked thermostat and dropped another one in and it did the same thing on the way home.

I flushed again and again. Clean. With cap off the the thermostat opens and level drops. I top off and rev RPMs but see no movement in radiator.

Screw it, order new pump and decide to change radiator too. I want no headaches later on.

New pump and radiator on today. While pump was off I flushed system again and it poured from both pump ports on the block as I filled from the heater hose. Clean.

Slowly filled system. Thermostat has a bleeder and I left heater hose at heater valve off and high up until water came out. Connected hose and topped off again. Started and let idle, no cap on, thermostat opened and level spit out and then dropped. I topped off and again, saw no movement in system. I put on a new CST 16 PSI cap and she stayed right in the middle of the gauge wile idling. Oh yeah, also installed new fan clutch and she is pulling air very well.

Drive and she goes right up but just shy of the first line on the right side of temp gauge. Come home and let her idle and temp drops slightly but not much. Slowly release cap, no pressure. Level is normal.

I unscrew threaded plug on top of water pump while running and cap off, just to the point where it is ready to come out and coolant is really starting to spurt out around the threads. Tighten and do the same to the plug on top of the thermostat housing, same thing. Rev engine and see no movement.

Drive again and come back and hoses are pressurized and gauge is same spot, just shy of first line or right on it. It was always in the middle before I started screwing around with it.

New lower hose and it has spring.

OK, could it be air trapped? How can I get it out? Restriction? Where?

Faulty sensor? When I disconnect gauge drops to left.

I plan on taking thermostat out when she cools down and see what happens.

Should I see coolant flowing through radiator at idle or by revving her up?

[cdowns]

you'll only see coolant flow when the thermostat is open// if you're worried about the temp of the coolant buy a cheap thermometer at the supermarket or bake shop or whatever they call them over there and see how hot it is . i'd suspect the gauge or if you're using water it will read somewhat higher than antifreeze

[neonlarry]

The part that I don't like is 'Slowly release cap, no pressure'. If it's not holding pressure it will heat up. I suspect you have a pinhole leak someplace.

[shelby987]

if you want to make sure the system itself is capable of keeping your truck cool, you could always pull the thermostat and run without it, if the gauge still runs to the high side of hot, I would say replace the gauge, if it goes to normal and stays there, you should start trying to hunt down any potential leaks in the system.
Are you running a recovery tank for the radiator, or an open hose to the ground?

[Blue85]

What size rad are you using? Mabye try a different rad cap also

[Longhorn Man]

are you reading a 35 year old guage, or a new aftermarket one?

[ChevLoRay]

As soon as you are able, get your hands on a Cooling System Pressure Tester. After attaching it to your radiator and with the engine off, pump it up to the proper pressure marking on the guage. Mine has a black marker for the pressures we run. Leave it at that pressure, and start timing, looking for a drop in pressure. Within one minute, it shouldn't drop at all.

If the pressure drops, you should be able to hear it leaking and see where it is leaking. If you see the leak, you can hopefully tighten up the suspect clamp or bolt(s).

Another possible source of overheating could be leaking combustion gasses, which leak into the coolant. Using the pressure tester again, attach it to the radiator and start the engine. Watch the pressure guage for rising pressures, although you may also be able to see bubbles in the coolant. Sources of such leakage could include a blown head gasket, for example.

Sounds like you have touched on all of the normal things to check.

But, like suggested earlier, get a cheap thermometer and check the accuracy of your other measurements. Don't trust the stock guage until you have an accurate measurement, based on a true thermometer that you can then reference your guage to.

[Boog]

Just for clarification, did it register fine before you decided to flush the system or did you flush the system because it registered high? No wait, I see this.
[Drive again and come back and hoses are pressurized and gauge is same spot, just shy of first line or right on it. It was always in the middle before I started screwing around with it.]
Could it be the temp sending unit in the head is in need of replacement now? Gauge was working before the flushing and now it's off.
Has there been anything else changed around this time?

[crustysarge]

I have a pressure tester and it holds pressure fine, held for 10 minutes and I released.

Stock old gauge, in fact, I am trying to find an aftermarket gauge I have buried in a box and hook up. I have not eliminated the possibility of a bad one.

Overflow bottle.

Tomorrow I'll dig a little deeper, bed time, hot and I'm tired. Thanks guys.

[Psycho71]

I would go get a cheap water temp gauge an install it temporarily. Or use the candy therm. trick. I suspect the chemicals damaged the sending unit. How old was it before you began?

I go thru this kind of thing every time I try to FIX something on mine. It seems like when I fix one thing, something related to it breaks or I find three other things that need fixin'. And of course it ends up costing three times as much as I had figured.

Good Luck,

Jay

[67Fleet]

My bet is on the sending unit if you find you have no leaks.

[cowboy33713]

Howdy;
in the absence of a pressure leak, my vote is on the sensor also- sounds like it may have gone south, or the wire for the sensor may have hidden damage. On my truck, the gauge needle would "dance" from time to time, solution was a replacement sensor. Running without a thermostat may cause overheating by letting the coolent, once it's hot, to pass through the radiator so quickly that it cannot shed heat while it's there. The old trick for chevy engines of drilling a SMALL hole in the round plate part of the thermostat does help get trapped air pockets to fill, though I've not had such a problem, I read that here last year.
Hope this helps.
cowboy33713

[hgs_notes]

I am a boiler inspector by trade and I think I might know what happened. If you had scale build up on the water side, it was also on the temp probe. When the scale was removed, it was also cleaned off the probe. Scale is an insulator and removing any significant amount will alter the amount of heat the probe sensed. So in effect, it was always running warmer than you thought. The stock gage does not show an actual temperaure, not with any accuracy anyway.

It sounds like everything is working great. You are trying to make it read a less accurate temp on the old gage. It will probably read like it did down the road again when scale reforms in the system.

HG

[crustysarge]

OK, today turned out slow, I got, umm, a little umm, under the weather. I went to the vineyard last week and bought 30 liters of wine to bottle and decided to drink more than I bottled today! Lost a few hours on the couch after eating potato salad and grilled sausage and fresh prosciutto ham.

I drained the system and took the sensor out, was fairly clean but I decided to take a fine brass bush to it and shined it up. Pulled the thermostat and pan tested in boiling water, good.

Ran truck with no thermstat and water is pumping very well through the 4 core rad.

Drove about 10 miles and temp stayed about 1/4 up on the stock gauge. Came home and let it idle 10 minutes and temp barely touched the 1/2 way point.

I will install thermostat tomorrow and see if I can scrounge up an external gauge.

I appreciate everybody's input. Not many car guys around here to BS with and work on stuff. Any of you show up in Italy let me know.

[cdowns]

you know it could be because you're over there and using metric water is the problem it needs good old american H2O

[Fred T]

Since you have your thermostat out, check it. Suspend it in a pan of water, I usually use a table knife and piece of string. The stat should not contact the pan. Heat the water and check the temp when the stat opens. Hold the temp for a minute or two, then allow the water to cool and check the temp when the stat closes. Both temps should be within 20*F of the temp stamped on the thermostat. They aren't very accurate.