IM gonna come unglued--PROBLEM-fresh build on my 1964 chevelle red on red convertable,anyway,350 crate motor with aluminum heads.Slowly gets hot until it has to be shut down.Restomod,so I had the stock radiator,changed to aluminum withan electric fan.Yes,has a fanshroud.Already changed the waterpump and 3 different thermostats opening ranges,160,180 and restrictor plate with almost no changes.Rechected timimg a zillion times then went old school with advance till labors starting then backing off.Standard rotation cooling.Used the chemical blok check verify no blown headgasket.Runs very well,sounds awesome...HEEEEEEELP.
a few things..do you have an infrared temp gun to VERIFY the actual temp of the various parts of the motor.....how much coolant percentage have you.. do you have one of the 3 buck coolant protection testers..? 50 percent coolant to 50 percent water.. to a better ratio.. 70 percent coolant to 30 percent water... does your radiator cap actually hold pressure?? 13 or 16 pound...do you have a coolant overflow tank and hose... so the expanding coolant is captured.. then when cooled off.. its pulled back into the motor.. do you have a bypass hose circuit.. from the intake crossover to the top of the water pump... as its a long way from the cylinder walls and heads to the thermostat.. the bypass allows circulation and heat to be picked up.. until it is hot enough to open the thermostat.. exchanging coolant with the cooler mix that was trapped in the radiator by the closed thermostat.... but wait.. as the hot and cooler is exchanged. the thermostat closes again.. this stops the coolant in the radiator... so the fan has a chance of cooling it... the bypass circuit also has a second not so well known function.. its smaller than the size of the flow of the water pump at moderate to higher engine speeds... what.. thats going to build additional mechanical pressure inside the block and heads.. take additional horsepower to do that.. yep... absolutely.... guaranteed.. but each pound of pressure raises the boiling point of the coolant 3F... so it there is 10 pounds of mechanical pressure behind the thermostat.. thats an extra 30 degrees of thermal protection before the coolant boils.. in places like around the exhaust ports... around the exhaust seats.. around the valve guides.... just think how much additional heat those parts get at full throttle or even just moderate loads .. how much would you pay to raise the boiling point of the coolant inside your block and heads by 30 degrees F and only at full load.. how much pressure will the water pump build behind the closed thermostat.. ? 10 pounds... i have not measured your engine with a pressure gauge in the coolant crossover ...did you ever try a 192F or 195F thermostat.. as with the increased horsepower more heat is created by the engine.. 230F to 235F is not unheard of operating temps with a proper ratio of coolant and water. a 192/195 thermostat.. a 16 pound cap... a coolant overflow.. and of course.. a properly designed bypass system.. infrared thermometers start at about 30 bucks.. many are available for 40 to 70 bucks... i have one of the 70 buck versons with the temp head on a long flex shaft... so i can bend it and stick it into places that are hard to get to... but the choice is yours... its an essential tool in any current tool box.. fingers and guessing does not count any more.. or you can invest in temp indicating crayons... that melt at specific temps... i don't know if they have a set that melts at cooling system temps.. i could find out.. but an infrared thermometer is far better... even works on arm pits.. last chance.. change to a 192/195 thermostat.. the last digit of the part number will be a 9... what's it going to hurt... with a 160 or a 180 thermostat and increased horsepower.. the thermostat cycles and cycles.. but the cooling system does not have enough temp differential with the ambient air to loose enough heat fast enough.. the thermostat they stays open.. the coolant flow through the radiator again and again faster and faster.. this is the thermal run away you are experiencing.. its hard to beat the laws of thermal dynamics... people will mention to drill a hole in the thermostat.. if you don't have a bypass circuit.. this is a good idea.. but it still is allowing circulation in the wrong direction.. instead of around and around inside the water pump.. block, heads and intake.. ..it just leaks a little right into the radiator.. the coolant can heat up in the engine.. it does not stabilize the whole system by continuing the circulation until it reaches the thermostat opening temp.. the 192/195F thermostat.. is the answer in most of the overheat problems lately when there is a cooling system runaway...if there is no bypass .. and your temp sensor is in the head.. you are seeing limited movement of the coolant.. print this in large letters.. tape it to the wall for you to reread.. sorry for being so random... this is not edited.. just comes out.... kinda like the coolant when it gets too hot..
I'm surprised you didn't mention the timing, it was the first thing that stood out to me as "This is your problem". A combination of too much fuel and too much timing will overheat an idling and cruising engine in a hurry. Keeps all the heat in the block. I'd retard the timing a fair amount, not knowing what cam and compression you have I can't say where I'd set it for sure, but in the range of 8* to 12* initial with no vacuum advance, and mid-30's all in with no vacuum advance. I'd leave the vacuum advance unhooked until the overheating situation is resolved. If that fixes it or makes it heat up slower, I'd be checking the fueling at idle and cruise, and are you sure it's not just pig rich? Do the plugs come out looking clean?
-The Silver Buick- '77 Skylark coupe w/ a Fuel Injected Buick 455&TKO-600, '72 Centurion Conv't - 455w/TH400, '67 T-bird 4Dr (suicide) w/428&C6. '69 Firebird replaced!http://www.bangshift.com/forum/index.php?topic=6189.0
actually makes total sense even though after several dozen builds I have neverexperienced the problem.However,because the heater works off the water pump and the intake manifold crossover,wouldnt it be the same if I just turned on the heater for the warmup circulation,all else being equal.Like changing the thermostat to 195,coolent ect?
I have had the timing all over the place,just to make sure the tabs were on or off.Doesnt smell overly rich and the plugs look spot on.
the heater system is part of the bypass circuit on some cars...front wheel drive chryslers used the bypass type heater control valves in the late 80s through mid 90s.. heater off.. the coolant just went through the hoses and back to the engine to compete the bypass.. but when you turned the heater on.. if the core was clogged.. the engine would start to over heat... i must have done 50 head jobs my self over the years because of this.. and radiator caps that did not hold pressure because of the loose center disc.. i only buy the versions with spring loaded center discs.. opening the heater control valve circulates the coolant in the heater and the engine.. but does not stop the run away issue as the radiator cannot cool the coolant when the 160 or 180 thermostat is held open by the coolant being hotter than it takes to close the stat to allow the coolant to stop in the radiator so the fans can take the heat out..change to the 192/195F stat.. and a 50/50 to 70/30 percentage that you have mixed from full strength.. verify the cap holds pressure.. that you have some kind of bypass.. you have tried everything else... thermostats are under 10 bucks.. gasket.. 2 or 3.. time to swap it.. 10 or 15 minutes on a cold motor usually.. the only other thing is air flow through the radiator.. there are several variations in belt driven fan blade diameters..there are more variations in the shape and the length of blades... skinny tapered blades don't always move enough air flow .. there are 5, 6 and 7 blade fans.. with electric fans.. please use 10 gauge wire to the relay contacts.. and 10 gauge to the fan from the relays.. the relay coils can be much thinner wires to control the relays.. if the electric fans do not move enough air.. it will not cool the coolant.. and a run away cooling system will happen..