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Overheating Dodge Ram 250

I have a '92 Dodge Ram 250, I recently replaced the freeze plugs, thermostat, and water pump. The van is running great but tends to overheat on the highway. It only seems to do it at speeds over 60mph. Everyone I talk to says that this is backwards but the van runs fine in the city. Can anyone help me please?

How many miles on this vehicle?

Did you also replace the radiator cap? If not, try that.

Descirbe “overheat.” Does it boil over?

Have you measured the actual coolant temperature, or are you just going by the dashboard gauge?

Maybe a new coolant temperature sender will give a different reading.

Overheating on the highway could be a sign of a leaking head gasket, but I’d explore all other options first.

About 100,000 miles on vehicle, I did not replace the cap. I have to test drive it tomorrow to see if it’s actually boiling over or if it’s just the gauge. My mechanic seems to think that it is just the gauge, but I do not understand why the gauge worked perfectly until I had this work done. Thanks for your input, I will let you know what I find out after my test drive.

If the coolant was so bad that the freeze plugs corroded through, then there is a good chance the radiator is pluged up enough to need replaced as well.

do you think a good radiator flushing may do the trick?

I suspect a new radiator will be needed…You can TRY this trick…REMOVE the radiator (assuming it’s a brass one, not plastic/aluminum). Lay it down so the ports are facing up and fill it with Muriatic acid, available at Home Depot and pool supply stores. Let it sit for a few hours or even overnight. The acid will not harm the brass or lead, but it will remove any mineral or iron deposits. Flush it out good and re-install. Be careful handling the acid. Dispose of the spent solution properly…Do NOT spill the acid on any masonry surface like concrete… A new radiator for your truck is not that expensive…