I have an ’89 LX, originally a 2.3L I swapped in an 85 5.0 HO about a year ago, the engine has mild modifications consisting of an E-303 cam, ported E7 heads, and a Performer intake with a 600 CFM Edelbrock carb. There is an overheating problem that only occurs at freeway speed (70 mph and above), around town the engine stays cool even idling in stop and go traffic with 95 degree ambient air temperature, the gauge never quite reaches halfway, its only when I travel at consistent speeds of 70+ mph for extended periods of time (30 minutes or more) that the gauge begins to slowly climb up to the 270 mark. If I pull off the highway and let it idle or drive around though normal traffic the temp falls back down to normal. As far as the cooling system goes, it employs a standard rotation water pump (stock  form a Crown Vic, as well as the rest of the engine accessories) the crankshaft pulley is a stock 5.0 HO used with a  specially machined 5/16” spacer to provide a 25% under drive for all driven accessories of the Crown Vic serpentine setup, the thermostat used is a 180 degree unit that is working properly, the fan is a 15” 94 Ford Taurus two speed electric fan (which pulls approximately 3400 CFM on the high speed setting) and is controlled by an Imperial electronic fan controller set at 205 on 180 off; the fan too is working properly, the radiator is from an ‘85 GT it is a 2 row core and was replaced a year prior when I pulled it form the donor car. As for everything else the carb is properly tuned, and a stock Duraspark ignition was also used, base timing is set to 12 degrees BTDC, and the car has a T-5 trans and 3.55 gears. One last thing, while in the driveway today and the engine warmed up I set the idle speed up to 2200 rpm and ran it for about 40 minutes the whole time the temp gauge did not go over half way nor did I observe any hoses collapsing, so the problem is only a concern when the engine is under a load. Would installing a stock Crown Vic crank pulley solve the problem, or do I need to upgrade my radiator to a 3 core, or would just upgrading the water pump do the trick?

Sorry for the long post but I felt it necessary to put all the information I could on the table.

you have covered all the basics.if you are certain the lower hose is not closing.make sure the fans are pulling air instead of pushing it.other than that all i can think of is to make sure the thermostat is facing the right direction.if this doesn't work post back and we will go from there,good luck.  

the reason i think it's the fans is beacause i have a '88 coupe with a 347.i can run my car on the freeway at 70 mph with the fans completly off and it will not run any warmer than normal.if your fans are pushing air it would not let any air flow in at freeway speeds ,but would work just fine around town.  

I am certain the thermastat is properly installed. The fans too are pulling air in, and the fans dont turn on untill the gauge creeps just past half way, and if I drive at 65 mph the engine stays cool and the fans never turn on but once I go over 70 the temp starts to climb, It also seems the harder I push it and the faster I go the faster the temp climbs. If I maintain 90 mph for a while the temp seems to climb alittle more quickly. I'm going to try changing the crank pulley today and see if that helps, but I'm thinking that the radiator being a 2 core is just not efficient enough to cool the engine under load. Seeing as though ford designed this radiator to be just bearly adequate for the 5.0 but plenty adequate for the 2.3. Because there is no EGR on this motor, at cruising speed the motor should experience higher EGT's on the highway, this coupled with the rised cruise rpm due to the rear gears may have pushed past the radiators efficiency to effectively cool the  engine down. What Radiator are you running a 2 core or 3 core?

i have a stock replacement 2 core from steeda that i installed when the car was stock.my car ,when run hard for anything longer than the 1/4 mile will start to run warmer than normal,but will slowly come down if i take my foot out of it.it could be that your radiator is ineffiecient,or it is simply not geting enough air flow for some reason.good luck  

well changing the pulley had no effect, which would leave me to believe that a high-flow water pump may not cure it either. I also stopped down at Second Street Speed in Perkasie, when I seen this shop was full of mustangs I knew these guys had to know what they were talking about. I talked to one of the guys down there, he said that the radiator is most likely the cause, while most mustangs they have seen have had their radiators upgraded already. The 2 core is really all that I'd need for short trips down the quarter mile, but defiantly not up to the task of taking on long duration highway runs or road course abuse. They recommened a Steeda 2-core double pass super cool radiator should fit the bill, and leave plenty of room for improvement, say if I ever wanted to add forced induction or nitrous. So it looks as if I'm going to have to order up a new radiator.

hi, just wondering if you have fixed the overheating problem? if not what kind of tranny are you using, and what is your rpm at 70 mph? also try flushing the radiator and check the cooling fins in the middle of it make sure it's not clogged with pine straw,dirt,etc. also check the radiator cap.   

well if you are going to get a new radiator i would get somthing like a be cool or a griffin.i need to upgrade myself, you mentioned the steeda 2 core,thats the one i have .while it is a good one i don't think, with your combo, you will have much room to grow .You did mention nitrous or supercharger.better to do it right the first time.  

radiator is on its way, ordered from summit yesterday, I ended up getting the 2 core aluminum custom fit unit (basicly th summit clone of the be cool) and to answer the rest of your qestions a T-5, 3.55's in the rear and just about 2000 rpm at 70 mph. I had flushed the radiator in October, looking down in the tanks I seen a little bit of scale but not bad, and the cap is new too.  

Well I got the radiator today, installed it after work. Had to cut the rubber mounts and modify the upper mounts to get it to fit (the summit unit is quite a bit thicker). Refilled the coolant and down the road I went. I hopped on the highway and ran it hard for about 20 minutes, varying my speed between 70 and 90, then I cruised it for another 20 minutes at a consistant 85 mph, the whole while the temp never creeped past 185 degrees. I'd say the problem is solved!  

sweet , you can rest easy now

I know that this is a late post but i'm new to this forum. Anyway another way that you can get your temp down is to install a colder thermostat. I use a 160 degree one and my temp never gets to the "n" on normal. FYI I have a 79 Mustang with the original radiator and a 5.0.