I was trying to bring my 1978 4.9L F250 home today after bleeding the radiator. It was idling ok for a little bit (five minutes or so) and was ok on the road for about fifteen minutes, then I came to a stop light and it either overheated there or shortly before it. I had been keeping an eye on the gauge and it was running fine for most of the trip. The radiator and water pump are original. I flushed the radiator and it was clean and I installed a new thermostat, but I'm wondering if the water pump is shot. Does that sound about right?

In my panic to get it off the road so traffic behind me could go, I tried to turn it over again and it gave that little attempt and it caught. I'm hoping it hasn't seized up.

 

If that water pump is the original that would be my first guess.

 

What made you think it was overheating?
Was it completely based on the gauge? Or other factors?

If it was the gauge, it could very possibly be the gauge itself. I've head "overheating" issues where the needle will climb WAAAY up (like almost to the far right) and then drop back down to normal.
If/when it does this, look at the other gauges and see if they follow suite. If you suddenly went from 1/4 tank to a 1/2 a tank, don't worry about your temp gauge.
If so, your voltage regulator in the dash is the culprit.

However, if it genuinely overheated with a freshly flushed radiator, I'd suspect the water pump as well.
However, it's still possible the radiator could be plugged. A flush is only going to clean out areas the fluid can actually pass through. If you have large parts of it fully plugged, it'll need to be replaced, or boiled out.

 

The gauge had been operating normally - nothing volatile, just a steady climb up to hot before I bled the system, then stayed in the normal range until I hit that stop light. All other gauges are operating normally. I had a fair amount of steam coming off the radiator when I opened her up. I'm guessing water pump. I ordered a new one and will install it this weekend. If that doesn't work, I reckon I'll have to boil and flush the rad or just get a new one. Thanks!

 

Is your coolant mixed based on your climate? should be 50/50. where i live with 110 degree summers i mix mine a tad rich just an extra splash of full strength, if i dont it will steam and get hot.

 

The "new" thermostat may be defective. It happens.

 

I can agree with that, anytime i put in a thermostat i boil it on the stove and watch it with an infrared thermometer. I have caught one that was defective.

 

I installed the new water pump and took a good look at the old one. The impeller looked good, aside from a small rust spot. The shaft spun easily and it seemed like it was in working order. I replaced it anyway with the new one and did notice some debris when I the coolant was draining out. I'm going to flush it again, but I'm pretty sure it's the original rad and might need to be boiled. Do most service stations offer that?

Thanks!

 

Not too many shops boil radiators anymore.

 

I had a garage look at it and they're telling me that I need a new radiator. This is the first time I've run it for longer than a few minutes and I'm not really sure what condition it's in. It doesn't leak at all and might just need a flush - I'm not sure if I'm getting taken for a ride or not. Here are the fins. Any feedback is appreciated.

 

Very well could be, I brought a rad in I thought just need the neck soldered up, and the guy explained how it had been leaking for years. The corners. They don't necessarily lose enough coolant to notice, but they won't hold pressure too well. They can be repaired sometimes, not always. Labor is expensive, and they can't guarantee success because it's 50 years old... you know the drill.

 

The fins is just 1 thing to look at.
Is there any green tint on the out side anywhere? If so it is leaking around that area and will not get any better.
The real place to look is inside the radiator. Can you see the tubes when you look in it?

Do they have any white crusty build up around them?
If so then the tubes could be plugged with that stuff and a flush will not remove it.
You can also get the truck up to temp, shut if off and feel across both sides of the face of the radiator.
You should feel the same temp across the whole face if not it is plugged.
Most of the radiator flush you can buy in stores will not do anything so save your money.

I used vinegar, its an acid, to eat at the crusty stuff. I removed it, did a quick flush with water & drained, capped it, laid it flat with the hose ends sticking up and filled it up and let is sit about a week.
I dumped it and flushed with water and repeted with fresh vinegar for a week again.
It did remove a lot of the white crusty stuff as you can see it when you drain it but that white crusty stuff was also holding it together.
As soon as I installed it and filled with water it leaked so I got a new one thru Rock Auto.

So as you can see you can do a quick check by feeling across the face if plugged but short of rodding (shop would remove a tank and run rods thru each tube to open them up again and hope they did not poke a hole thru them) or re-coring (shop removes the 2 tanks and installs them on a new tube & fin "core") there is no real fix.

BTW the old radiator was copper / brass the new is plastic / copper and is cooling just fine.
Dave ----

 

Looks like it was the radiator! New one is working well. Thanks for the assist.

 

Awesome! Old one must've just been plugged up beyond fixing with a flush.
Glad you're keeping it cool and off and running. Thanks for the update.