If it is good when moving then it has to be air flow through rad.
I had same issue on mine but since using flex fan temp don't go above 180 even at idle.
I had electric fans on, not enough air flow.
Advice needed
Moderator: Moderators
1) too little initial advance
2) running rich at idle
3) too low thermostat setting, should have 190F in there
4) too big crank pulley too small fan/pump pulley, running too fast
5) bend tangs on filler cap
no.3
your cooling system is working too well in respect to throughput and poorly in respect to temperature control.
if you put in a 145 or 165 or 175 then it starts to open 5-10 before that and allows the water to rush round
(or you stat is stuck open
or it has a big hole in it
or you have no thermostat
or its stuck closed....it could just be closed)
even when you start to overheat the water is still rushing round and is uniformly warming up with the motor, no difference anywhere,
its stays rushing round because the stat never closes..... the water slowly heats up and up and up along with the heads, but never cools enough with just fan air flow through the rad because it never stands still in the radiator.
At idle all parts of the system end up the same temp so nothing cools.
you are already in a vicious circle.
it cools when you go fast enough, because going fast forces much much much more air than a fan ever could through the radiator.
if you put a 190F stat in
the water spends its life being "staged". The stat futters off and on when necessary its not jammed wide open from a slightly warm temperature. it instead does what it is supposed to do, which is vary the flow constantly at the operating temp of the engine.
so water stays longer in radiator and Blurts!!!!! through in a constantly modulated or pulsed wave to cool the motor when the stat flips open closed open closed .
and the system works better the higher the pressure, the pressure in this system will be high from the point where the stat starts to work, higher pressure in essence makes the water wetter. With a low temp stat the pressure is not held constant it fluctuates widely blowing water out the vent which assists with further venting and overheating. because your one and only control on the system is stuck in the open state from a point where the engine was just warm, it might as well not be there.
too hot
stat open
flood of cool water
too cool
stat closed
warm up again in motor
cool off in radiator
too hot
stat open flood of cool
the cool water stays in place long enough to do some good and is then pushed when hot, back to radiator by the next big BLURT of cool water in, to spend some quality time there cooling down.
4) unless you have a crazy mismatch or custom pulley set up your system is designed to work from 700 rpm to redline above that and you waste fan HP and risk cavitation in the pump (pac-man like vacuum bubbles that eat cast iron and aluminium) if you run at 3000-8000 you need a smaller crank pulley or a bigger pump pulley so that the water pump and fan still run at the same RPM as they did previously.
5) bend the tangs on the filler cap. these days with mine i don't care if its new, if it has a rubber or tin plate seal... if the top tank spout is 40 + years old it will be worn and potentially will not clamp the cap on properly. they are supposed to be a struggle to get off and on, and the cap should seal the top of the spout. the rubber plunger and spring control venting if the cap sits too high due to worn section in the rim that spring pressure is too low.
Dave
2) running rich at idle
3) too low thermostat setting, should have 190F in there
4) too big crank pulley too small fan/pump pulley, running too fast
5) bend tangs on filler cap
no.3
your cooling system is working too well in respect to throughput and poorly in respect to temperature control.
if you put in a 145 or 165 or 175 then it starts to open 5-10 before that and allows the water to rush round
(or you stat is stuck open
or it has a big hole in it
or you have no thermostat
or its stuck closed....it could just be closed)
even when you start to overheat the water is still rushing round and is uniformly warming up with the motor, no difference anywhere,
its stays rushing round because the stat never closes..... the water slowly heats up and up and up along with the heads, but never cools enough with just fan air flow through the rad because it never stands still in the radiator.
At idle all parts of the system end up the same temp so nothing cools.
you are already in a vicious circle.
it cools when you go fast enough, because going fast forces much much much more air than a fan ever could through the radiator.
if you put a 190F stat in
the water spends its life being "staged". The stat futters off and on when necessary its not jammed wide open from a slightly warm temperature. it instead does what it is supposed to do, which is vary the flow constantly at the operating temp of the engine.
so water stays longer in radiator and Blurts!!!!! through in a constantly modulated or pulsed wave to cool the motor when the stat flips open closed open closed .
and the system works better the higher the pressure, the pressure in this system will be high from the point where the stat starts to work, higher pressure in essence makes the water wetter. With a low temp stat the pressure is not held constant it fluctuates widely blowing water out the vent which assists with further venting and overheating. because your one and only control on the system is stuck in the open state from a point where the engine was just warm, it might as well not be there.
too hot
stat open
flood of cool water
too cool
stat closed
warm up again in motor
cool off in radiator
too hot
stat open flood of cool
the cool water stays in place long enough to do some good and is then pushed when hot, back to radiator by the next big BLURT of cool water in, to spend some quality time there cooling down.
4) unless you have a crazy mismatch or custom pulley set up your system is designed to work from 700 rpm to redline above that and you waste fan HP and risk cavitation in the pump (pac-man like vacuum bubbles that eat cast iron and aluminium) if you run at 3000-8000 you need a smaller crank pulley or a bigger pump pulley so that the water pump and fan still run at the same RPM as they did previously.
5) bend the tangs on the filler cap. these days with mine i don't care if its new, if it has a rubber or tin plate seal... if the top tank spout is 40 + years old it will be worn and potentially will not clamp the cap on properly. they are supposed to be a struggle to get off and on, and the cap should seal the top of the spout. the rubber plunger and spring control venting if the cap sits too high due to worn section in the rim that spring pressure is too low.
Dave
Last edited by Dave999 on Mon Sep 21, 15 5:47 pm, edited 5 times in total.
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MilesnMiles
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In addition to Daves points, I had an overheating block and that was as clean as they come with clean water/coolant and no rust.
Ali rad ( you have that)
180 degree stat form Real Steel, heavy duty compared to what's was I it previously.
Hemi clutch fan, the big one which was correctly distanced from the rad.
I never see over 180 in normal driving. Sumer and stopped traffic and never got beyond 195.
I later fitted aftermarket heads with better cooling jackets, but the improvements worked even with my 40 year old J heads.
Ali rad ( you have that)
180 degree stat form Real Steel, heavy duty compared to what's was I it previously.
Hemi clutch fan, the big one which was correctly distanced from the rad.
I never see over 180 in normal driving. Sumer and stopped traffic and never got beyond 195.
I later fitted aftermarket heads with better cooling jackets, but the improvements worked even with my 40 year old J heads.