uhhh yup.. engine timing was going to be my next bit of advice based on the response to my questions. The easiest and best way to troubleshoot this VERY likely cause is to hook up a vacuum gauge to a full manifold vacuum source and see what retarded spark advance is doing to the engine. Any stock engine in even halfway decent running condition should be well more than 15-16 inches. A fair condition and decently tuned stock cammed motor can be well over 18 inches. Another very easy trick to alleviate some of this issue without tossing money at the wrong problem is to make sure that the distributors vacuum advance is hooked to FULL manifold vacuum source. NOT a ported/timed source which does absolutely nothing for idle speed spark advance. When you get it right and hooked up to full manifold source.. the engine will idle up faster and you'll need to reduce the idle speed set screw to bring it back down to around 650-700 neutral rpm. And then the idle mixture screws will need to be readjusted(might already be misadjusted to begin with and just add more insult to injury when timing gets advanced). Vacuum gauge tells you what the engine likes best.. just set it to highest and smoothest vac gauge reading or listen/watch closely to audibly smoother ignition firings and vibration levels while you set it be ear. Besides obviously hooking up the vac gauge first.. an easy way to tell(if you have no gauge) which port is which is to unplug the vac advance pots hose and put your finger over the port to feel for vacuum. If there is no vacuum then you have it hooked up wrong to the ported/timed source which only comes into the picture when the engine revs up past high idle/during cruising speeds. That alone can make a substantial difference in idle speed coolant temps. The shroud will greatly improve these less than efficient antiquated designed downflow rads since it allows airflow past more of the core when the car is not moving. Another trick to help these older rad designs, or any cooling system design for that matter, is to use a water wetter type cooling additive. They work by reducing the waters surface tension and improve heat transfer efficiency. And unless you need to run the heater in the wintertime.. the highest temp t-stat you should be running in the summer heat is 180° max. Running anything hotter only helps emissions and reduces the safety margin before the car starts getting hotter while sitting still.
... should most definitely be checked. Or replaced because its so easy/cheap to do and considered basic maintenance/cheap insurance to begin with anyways.
In almost 50 years of vehicle ownership, I've never seen a engine with stuck thermostat cool down when revved... It's going to get hotter if the coolant can't circulate...
Might not be the problem but will add my .02, I tried several times to run a Flexilite fan on my Bronco, which had an upgraded 4 core radiator without a shroud, and it would not run cool unless I was cruising at highway speeds of 55mph or more. As soon as I installed a shroud and a direct drive factory fan it will not overheat at any speed. I threw that fan in the scrap pile.
No they don't. And that's the problem. lol Seriously though.. I've run them many times on Mustangs, Cougars, and Fairlanes among others with absolutely 0 issues. Of course these rads are even smaller yet.. but just giving perspective. And that was before all the new chemical technology we have to help us out even more these days. Cooler t-stat helps a bit but you need to have the tuning right to really make it work well.
Are you losing any water/coolant? First thing I would check is the oil for any water after a severe overheat. As far as the temp difference there seems to be a blockage somewhere. When I bought my last comet it would over heat, the water pump was clogged with a thick sutt. I swapped the water pump out and it was nice and cool afterwards. I also removed the petcock and ran water through the radiator as the car warmed. Helped get some of the crap out. Good luck.
It's ok I'm just,ASE master and Ford senior master and GM certified and do it ever day for a living. I'm sure you are correct.
Would you care to explain how coolant exits engine into upper hose and into radiator when thermostat is stuck???
"Stuck" open? Or "stuck" closed? If closed, all the ASE certification in the world won't change the laws of Physics.
Rpm increases water pressure enough to push past it. The cool water exits the radiator and drops the temp momentarily until pressure drops, the water stops and heats back up fast. Saw it a million times and replaced the thermostat. I'm not gonna say some thermostats won't be so jammed up it can't or won't move but iv done this a lot of times. If it's a head gasket and you Rev it it will puke immediately or if a guy wanted to he could do a lithness test to check for exhaust gasses in the cooling system.
Million times eh?? You work must on a lot of cars, have any time to actually fix one??? If you'd note first post, excepting for water pump, everything in cooling system incl thermostat has been replaced...
20 plus years feels like a million times. We actually diagnosed and repaired a thermostat in a vortec blow vetted today. Just like this...... like always it's a pissing match here. I'm sure you can fix it for him right from your keyboard.
