I have a 92 Bronco 351W with 191K and it tends to run hot. Just before Xmas I was running down the highway about 75 for 1 hour and stopped for gas and coolant starting running out the overflow. Started and the gauge read hot. After about 5 minutes on the highway everything was OK. Got home and changed the Rad cap and thermostat. Everything OK until the warm weather hit about a week ago. Same thing only at 70 MPH. Removed and cleaned radiator, and air cond coils, everything looked good. Engine still will run warmer than normal at 65 and will jump 1 letter on the "normal" scale if I speed up to 70. Run air and you will see it jump almost instantly a letter. Run heater and it will drop a letter. I am getting coolant flow thru the radiator and the fan works fine. It will go up letter when I have a load (Uphill). When I exit the highway the guage will go up. I removed the thermostat and it works fine in boiling water. I ran with no thermostat today and ran cool for a long time and then went to normal temp and then after 15 miles it went back to a cooler temp. Removed water pump and it looks good. Will install new waterpump, new thermostat, and temp sending unit tommorrow. Any other ideas?

 

You say you cleaned the radiator. Did you flust the complete cooling system? Have you tried changing your thermostat? I had the same problem. I bought a can of Prestone Super Flush, and followed the instructions. While running my truck with the heater on (as per instructions) I could feel the air blowing out hotter and hotter. Must be the water passages in the radiator, engine and heater core get a deposit in them. Evidently this lowers the cooling efficiency of your cooling system. I also changed the thermostat and gasket for good measure. Now I can cruise down the interstate at 70 plus, and the gauges stays down where it belongs.

 

Check the front of the grille, make sure there's no blockage, from debris and such and the fins straight. The fan is another thing to check even. Just because it's turning does'nt mean it working properly. While you have the water pump off, clean the clutch on the fan real good. It works thermally. After you get it together, take a large piece of hose about a foot long and drag it on the fan blades while it's running and see if the blades slow down fairly easy. If it just bumps the hose, it should be good. Make sure you look at the direction of rotation before doing this as not to stick the hose to where the fan will rip out of your hand. I saw a guy at a radiator shop do this. Convinced me I had a bad fan. Put a new on and never had the trouble again. Be careful.

 

The fan clutch should be stiff when the engine is hot and kind of free when the engine is cold. An engine flush sounds like a good idea. You might leave the hose on the fan while the engine is running to the experts.

 

make shure your bottom radiator hose is in good shape, if its very soft and dose not have the reinforcement wire in it then replace it, a cheap bottom hose with out wire in it can colapse at higher speeds, the pump sucks through that hose. DW

 

I have changed the parts. Now I am having problems with no flow. My guage works better. The water pump is pumping, I am getting good flow thru my heater and thru my intake. What I am getting it seems is water backup thru my bottom hose to the radiator. The radiator is not clogged. I have a new thermostat and verified it is not in backwards. I have tested it again in boiling water and it works as advertised. I think the fan is bad. I cleaned it and it worked good, but it seems to stop working when it is cold. The fan works when cold then when the engine warms up and it starts to slip. I will change it also. I am going to flush the system today and remove the thermostat again (6th time 2 thermostats) and run the enigne without it to check flow again. I think I may have a air pocket problem.

 

Just "bite the bullet" and buy a new triple core radiator! At almost 200k it's about that time. ...mike

 

Some of the passage ways in the head gasket are small and maybe a quick flush isn't good enough. Seems like I have seen some kind of pressure flush using a water hose and a fitting..

 

Well all seems to be going well. Changed the fan clutch, took the truck out and it seems to work fine even with the air on. Got gas and the darn starter went out. At least I was not far from home and the starter was on warranty. I will have a good check on Monday while I drive to work (50 miles). Does anyone know about the two bypass outlets on the waterpump. I hooked them up wrong the first time. Could this cause a problem?

 

Just an update. Changed the sending unit helped the guage work normally. Changed the fan clutch and the overheat at low rpms went away. I changed the cap, thermostat and water pump, these were all OK. I still had problems after all of this with the engine running hot after about 20 miles in weather above 60 degrees. Could not use the air cond and had to turn on the heater full hot to stop an overheat. Finally took the radiator to get it cleaned out. The radiator was 50 percent blocked. At least I have a good cooling system for the summer. Thank you every one for your help.