I have a 1994 E350 Box truck that I purchased for a move.When I picked it up it was running fine at idle but when we got it on the highway it started to run hot,I didn't let it over heat and had to stop to let it cool down three times to get it home.When I got it home we started to check it for a problem and if I let it sit in the driveway it will not run hot but if I drive it around it slowly start to run hot then overheat.To date we have flushed the rad 4 times,changed the clutch fan,tried a less pressure rad cap,checked the water pump and it seems to be just fine,checked the hoses and the bottom one is soft but doesn't collapse and have installed and removed a new thermostat.We are puzzled because like I said if we let it idle in the yard for hours it will run normal but as soon as we take her out on the road or sit and raise the idle to a higher rpm in about 15-20 min she starts to slowly run hot,turn her off and let her cool down and like I said before start her up and idle for hour with no problems... Can someone help me with this problem. :(

Did you perform a compression test on the engine? My next move, based on what you have checked or done this far, would be to suspect a head gasket. I believe there where about four different engines offered in that model van and I am not sure which one you have. You could also check for bubbles in your coolant resirvor, especially if someone raises the engine RPMs.

Good Luck,
MOrrowrj

I suspect you need to have the radiator rodded or replaced, due to corrosion or mineral buildup. Only use a 50/50 mixture of coolant and distilled water.

Also Ive seen a soft hose that appear to be OK but the inner lining of it was collapsing.

You definitely have a flow problem. Coolant needs to be "on the move" when needed most and that's at upper rpms/warmer temps. As the PH balance in coolant decreases, it becomes more acitic. Eating metal and plastic internal parts. Coolant is very important and most ignored.
Like Tex said, next step, radiator R&R. Don't forget the new upper/lower hoses!

I have a 1994 E350 Box truck that I purchased for a move.When I picked it up it was running fine at idle but when we got it on the highway it started to run hot,I didn't let it over heat and had to stop to let it cool down three times to get it home.When I got it home we started to check it for a problem and if I let it sit in the driveway it will not run hot but if I drive it around it slowly start to run hot then overheat.To date we have flushed the rad 4 times,changed the clutch fan,tried a less pressure rad cap,checked the water pump and it seems to be just fine,checked the hoses and the bottom one is soft but doesn't collapse and have installed and removed a new thermostat.We are puzzled because like I said if we let it idle in the yard for hours it will run normal but as soon as we take her out on the road or sit and raise the idle to a higher rpm in about 15-20 min she starts to slowly run hot,turn her off and let her cool down and like I said before start her up and idle for hour with no problems....Can someone help me with this problem. :(
Yea I think I'm going to have something done with the rad tomarrow morning.I'll let you know how it goes...

Thanks for the help guys.It was the rad that was pluged up,Bought a new one ane flushed out the motor .Now it works great,I'll remember to keep a better eye on that.