So I put quite a few miles on my Bronco today. Many of them were hwy miles heading east on I-76 (so flat). With the heat today and running the cruising speed up to around 70 or so, RPM's between 2700-3000 on the 3 spd., my engine was running around 225F. I did back it down a bit to cruising closer to 65 and 2500 RPM and it dropped the temp down to around 220F. As soon as I would get off the hwy and drive typical city driving, the temp would drop down within 5 minutes to between 210-215.

It is my understanding that with EFI, it is supposed to run hotter but what is an acceptable range? I'm running 351W with Explorer EFI.

I have never seen any "hard" rules for MAX engine temp. I used to own several Ford Cologne V6s, which were notorious for cracked heads from over heating and most of mine ran hot.

I kept my engines below 220°F. Above that, and I was reducing power to lower temps. I would shutdown or idle an engine over 230°F. Most engines I've been around will start having pinging problems above 220°F.

That being said, we used to have a Chevy 350 race engine in the University's circle track car and that thing would come back to the pits with water temps over 250°F and oil temps 290°F+. Now I can't speak about it's longevity at those temps, but we never blew one up outright.

My Bronco's 351W currently is mildly built with cam, headers, intake, heads, etc. With a 195°F thermostat and a Champion (I think) aluminum radiator, it tends to be over-cooled. On hot summer days, engine temps vary between 185-195°F. Cold winter days, I'm lucky to hit 185°F.

Experience with my Ranger says that radiators make all the difference in the world and not all aftermarket units are equal. I chased cooling problems in that truck for years, only find out the super duper 3-core radiator I put it was no better than the crusty 1-core that came out. A different 3-core radiator would allow me to run WOT up Vail pass fully loaded all day.

im going to guess that you may still have air trapped in your cooling system from changing parts, etc.

Put it nose up with radiator cap off.

Run it for a while to let it warm up enough to cycle the thermostat at least a couple of times. Keep topping the radiator off with coolant. When the thermostat closes, fill up the radiator and put the cap on and let it run a a bit longer and watch the gauge.

Make sure the suction tube is sitting on the bottom of the overflow / expansion reservoir so that it is always submerged in coolant. Fill reservoir up to hot level and drive it around to get the thermostat to cycle a couple times again.

Then let it cool off completely making sure to keep topping off the reservoir so the suction tube can only pull in coolant.

If you have a pocket of air in the cooling circuit, the temp sensor will read hot as it is getting a false reading from the steam.

Stock gauge? Maybe check it against a 2nd source, IR temp gun could work.

I don't like to see any higher than 220 with 195-205 being ideal.

At 65mph you should have plenty of air flow so it's not likely to be a fan/shroud problem. The T-stat is working if the temperature drops back down to normal. So, I'd say the radiator just isn't transferring heat well enough. Before replacing it look at it. If it has debris stuck in it try cleaning it. If a bunch of the fins are bent they can be straightened, but I'd just buy a new radiator at that point.

I had the exact same problem. Dropped in a champion radiator for about $185 and haven't seen a temp above 195 since. Ran about 125 when my thermostat failed item.

What kind of RPM's are you running in city driving?

I'm thinking your water pump is having problems with cavitation.

So I just got back from running some errands and around town I am staying around 200F. The water pump is brand new and I would say my RPM's vary around town but I would say I am consistently around 2200 or so. I can get the Champion radiator shipped with the 5.0 conversion for $195.

The radiator I have now looks to be in good shape -- the fins all look pretty good and there is nothing stuck in them. I had the inlet/outlet switched out when I converted to the 5.0 serpentine and the Radiator shop said it looked to be in good condition as well. Maybe it just can't keep up with my new engine with bigger balls!

I have a feeling I will be getting the new radiator. For the people running the Champion 3 core radiator. Where did you buy the new mounts? I was thinking of getting them from JBG as they also have dash knobs I need to buy. I've seen some write-ups on CB that some of the mounts have not worked for people out of the box on the Champion radiators... looking for insight if anyone has had success or problems.

intuition tells me it isn't the radiator

I used the 4 core radiator mounts and they fit the radiator perfectly. Worked great. Rox could be right, it may be something else, esp given that the radiator shop checked it out. 351w do have higher cooling needs, so the existing radiator could have been good enough for your 302, but just not quite enough for your new engine.

If it were the water pump cavitation, wouldn't the engine overheat on the hwy in "cooler" than 95F weather too?

I'll add a couple of items that I think you should check; fan clutch and H2O/coolant percentage. The more items you are able to confirm are correct the smaller your list will get.

I need a new radiator,where can I buy a champion from?

The fan clutch should be controlled by a small thermostat, more importantly it shouldn't be worn out (i.e. bearings) and should operate correctly, spin freely when the temp is low and engage when the temp is high.

So I replaced about a gallon of coolant today with water to increase the water to coolant ratio. I propped the nose up and ran the engine to temperature with the cap off. It didn't seem like their was air in the system, but I let it cycle a couple of time and as it overflowed into a bucket, I added a little bit more water.

I then went off on a test drive on I70 Westbound towards the mountains. I started at Wadsworth and got off at Youngsfield/ 32nd because it was clearly overheating. Once I got on to 32nd, I drove that home for about 7 miles going about 30 mph in 2nd gear keeping my RPM's up around 2700. The temperature maintained a "comfortable" zone of 200-210ish. Even sitting in my garage getting to a warm temperature. It seemed to idle above 200F.

I appreciate the suggestions-- I have a new radiator on order as it seems that this radiator is having a hard time keeping the temperature down during hot summer days. I am hopeful that my new aluminum radiator will have the same effect that it has had on Justin, Digger, and TOOLMAN.

stupid question but in all your times tearing down the engine did you put the t stat in backwards?

Doesnt mean it's not backwards. Mine was backwards and it still opened. Did this problem just start?