Help on normal operating temps on daily driver OEM 5.0

MrPerfect2

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Jul 23, 2019
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Washington DC
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91 GT vert - auto - 327 gears , clean engine with stock fan shroud and stock lower radiator air deflector, new heavy duty fan clutch , new 192 thermostat ( not drilled ) new rad cap , 50/50 blend coolant , stock overflow tank , newer stock size radiator , older water pump - using a mechanical water temp gauge hooked into temp sender intake manifold port . During Ambient air temps around 97 degrees w/ 50% humidity . Car runs about 200-210 in stop and go traffic . Runs 220-225 on highway cruising . Held 185 degrees for 30 minutes today thru traffic - today’s temps are 75 degrees - should be 80 degrees this evening on highway trip home ( will know later how those car temps are ) I heard the cars computer prefers minimum 195 to run best ? Question I have is it unusual and unsafe to be at 225 when outside air is mid 90s with higher humidity ? How come highway cruise is higher temps then city ? Thanks for input
 
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Modern EFi engines run around 200 degree. Running around 210 is still somewhat normal but I would start keeping an eye on the guage. At 220F, I would be trying to do something about keeping the temps lower.

What's the condition of the radiator? Is it new? Old? Gunk in the fins internally? Bent fins on the radiator itself?
 
Radiator “looks” about 5 years old - fins are not bent - flow is strong when cap off before it got hot - I am going to spray some degreaser on radiator and wash any dirt out of fins this week and try the burping air out parking on incline then .
 
I am a bit confused on the whole “closed loop” principle - I heard the ECU runs open loop until certain temperature - how does this work ?

Open loop refers to vehicle warmup where sensors get ignored and the car runs on ECU programming during startup. It tends to run a little richer, which is why the exhaust note tends to seem a bit "fuller" and more appealing.

Close loop occurs at different parameters depending on the vehicle. For the Mustang, around 140-150F or so it will switch over and now rely on sensor inputs to control fuel trims. Some claim it happens at 180F, but I've seen someone break down the coding in the A9x family and it's actually pretty low.
 
I did the burp procedure and added some foam weather stripping to close a gap around edge of fan shroud where it contacts the radiator - there was a 1/2 “ open because my fan shroud mounting - I figure this will force the fan to draw more air through radiator instead of through gap around it
 
I have changed coolant , but not force flushed - when I burped it last night and level dropped when thermostat opened , the flow appeared strong . Cruised in to work steady 182-188 degrees , 30 min drive in traffic . Ambient 70 degrees - keep in mind , I got stock iron heads and 192 thermostat .
 
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I have changed coolant , but not force flushed - when I burped it last night and level dropped when thermostat opened , the flow appeared strong . Cruised in to work steady 182-188 degrees , 30 min drive in traffic . Ambient 70 degrees - keep in mind , I got stock iron heads and 192 thermostat .
Sounds good 2 me:) Sometimes these 302s are hard to get ALL the air out after flushing.
 
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in a perfect world coolant temp should be 212 degrees f for gasoline, slightly hotter for e85

on a stock foxbody ----
if engine coolant temp (ECT) is below 56 deg then it wont go in to closed loop til coolant temp gets up to 136 degrees

if ECT is above 56 and less than 170 at startup then it goes in to closed loop after 100 seconds

if ECT is greater than 170 at startup then it goes in to closed loop after 60 seconds
 
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I think I just added an extra cooling core , lol - ran heat on low - outside air 90 degrees ( top down convertible so heat all feels same to me ) dropped water temps to 204 cruising in and out of city for 30 min straight
 
The ECU, closed loop, open loop, has NO control of the cooling system. The thermostat regulates to 192. If it can not, this the problem you are looking for.

MrPerfect2, if you only have high temperatures on the highway. I'd start with a radiator. As they age and have build up on the inside of the cores, they lose their effectiveness to cool the water.