skydawg Posted September 7, 2023 Share Posted September 7, 2023 (edited) The temp gauge in my 673 ENDT is at 140 deg after 20 min on the road,in 85 deg weather,shutters still closed.The shutters seem to work,open when sitting cold,then close when air builds,but don`t open after that.I figured my temp gauge must be off,that I must be fully warmed up after 20 min.If the gauge is wrong and the temp is more like 170,then maybe the shutter stat is bad? Edited September 7, 2023 by skydawg Quote Link to comment Share on other sites More sharing options...
terry Posted September 7, 2023 Share Posted September 7, 2023 2 hours ago, skydawg said: The temp gauge in my 673 ENDT is at 140 deg after 20 min on the road,in 85 deg weather,shutters still closed.The shutters seem to work,open when sitting cold,then close when air builds,but don`t open after that.I figured my temp gauge must be off,that I must be fully warmed up after 20 min.If the gauge is wrong and the temp is more like 170,then maybe the shutter stat is bad? Check on the thermostat, thermostat has to be about 10 or 15 degrees cooler than the shuttstat, if your really working the engine the thermostat opens first, if still to warm then the shutter stat opens shutters and cools it down. Terry 1 Quote Link to comment Share on other sites More sharing options...
Brocky Posted September 8, 2023 Share Posted September 8, 2023 After you have worked it fairly hard pull over and check both sides of the thermostat and the shutterstat with a hand held heat gun. This will tell you if your gauge is off or where something like the thermostat are NOT opening.. Quote Brocky Link to comment Share on other sites More sharing options...
mowerman Posted September 8, 2023 Share Posted September 8, 2023 I wonder if the shutter stats are still available last one I bought was 40 years ago exactly F model. Good luck bud. We just went thru this with H67 his plan was a genius ha ha not surprised… bob Quote Link to comment Share on other sites More sharing options...
JoeH Posted September 8, 2023 Share Posted September 8, 2023 If the truck is empty and not working hard then chances are it's right. 85 degrees outside is waaaaay cooler than the 180 degrees the engine thermostat should be functioning at. It is possible you don't have a thermostat installed, allowing unrestricted coolant flow. This paired with a fixed radiator fan (no fluid clutch) and you'd have to work very hard to heat that engine up. Only way to check to see if there's a thermostat installed is to pull the upper radiator hose off the engine and look in. 2 Quote Link to comment Share on other sites More sharing options...
JoeH Posted September 8, 2023 Share Posted September 8, 2023 If it does have a thermostat then it could be stuck open too. I forget how this thermostat is shaped, I had one that a chunk of the rubber seal around it had failed. Engine almost never got up to temp, and cooled back down quickly if it wasn't kept working hard. 1 Quote Link to comment Share on other sites More sharing options...
mechohaulic Posted September 8, 2023 Share Posted September 8, 2023 I agree with no/bad thermostat. a faulty shutterstat would result in over heat if shutters were required to open and didn't. have seen thermos that came apart resulting in basically a non functioning thermo. should be a shut off valve near firewall on line going to shutter stat; try closing it to keep shutters open. temp possibly will not even hit 140. pull thermo housing off ; if thermo is there but broken apart attempt to find all the broken parts. most time the brass rivet wears out , that's lost in system .water pump impellers take care of it. as stated above the rubber seal has been found jammed also keeping thermo in open position. Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted September 8, 2023 Share Posted September 8, 2023 Rule of thumb, again from the late Glenn A, if the shutter thermostat is in the upper tank, it should be 10 deg higher than the engine 'stat if in the lower tank (as some are) it should be the same temp as the engine stat. Your situation sounds like a bad (or missing) engine thermostat, shutters are doing all they can to get the temp up (staying closed) Quote Link to comment Share on other sites More sharing options...
HarryS Posted September 8, 2023 Share Posted September 8, 2023 My '60 doesn't have a thermostat or even a provision for one. The truck was sold new in Atlanta. It runs usually at 170 even on the hottest days but on a long hill the shutters will open. They also open when the engine is shut down and temp goes up. Quote Link to comment Share on other sites More sharing options...
h67st Posted September 8, 2023 Share Posted September 8, 2023 My shutterstat says 180° but my gauge says 190° when they open. At first they didn't open at all but I took apart the shutterstat and found corrosion inside, cleaned it up and lubed the pin and now it works well. There is no tstat ('58 model 673 NA). 1 Quote Link to comment Share on other sites More sharing options...
h67st Posted September 8, 2023 Share Posted September 8, 2023 Watts has shutterstats for $250. https://wattstruckcenter.com/shop/b-model-parts/b-model-mack-engine-transmission-and-driveline/shutterstat Quote Link to comment Share on other sites More sharing options...
skydawg Posted September 8, 2023 Author Share Posted September 8, 2023 My truck is a `61,so maybe no thermostat,like Harry`s...I`ll check and see. Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted September 8, 2023 Share Posted September 8, 2023 Some engines had a 'stat that is clamped in the upper hose near the engine outlet. Quote Link to comment Share on other sites More sharing options...
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