So I have replaced the thermostat and water pump.
It will run fine when going down the highway or any speed over 30mph.
But as soon as I get going low speeds or sitting it over heats


My next thought was to replace the radiator.

The engine is a 347 stroked motor and Im running 91 octane in it.


Anyone else experience this problem ?
What should I do to cure it?

CARB I assume ?

1) confirm t-stat is working properly, lots of new ones don't quite open up completely
2) full circle shroud with fan penetrating into shroud about halfway
3) spacer under carb
4) fuel supply hoses / tubing to carb routed away from engine / and exhuast
5) fuel supply hoses / tubing wrapped in heat shielding or redneck aluminum foil
6) fuel lines from tank routed away from exhuast system on driver's side
7) convert to electric fuel pump

face it, you need to go EFI !

Are you running a clutch fan? If so you may not be turning at lower speeds.

Before replacing the radiator I would pull it and give it a good flushing.

No clutch fan Its a 7 Blade flex and it does have a shroud.
I have drained the fluid 3 times now and put new in each time.
the radiator looks brass to me and maybe the original or OEM.

I have a question are you running v-belts or serp. set up? You might have the wrong water pump. Alex

Are you sure that you have the correct pump. If it is the wrong one the pump would be turning the wrong way

If you remove the radiator cap and park it nose up so that the radiator is the highest spot and let it run for a while so that the thermostat has an opportunity to do its thing a couple times.......you should be able to make sure you get all the air out and see if the radiator has good flow (if not, might be time to have it tested and cleaned).

Also, flex fans are notorious for doing a poor job cooling our Broncos. If you could find an OEM fan with fixed blades that would be the best. A clutch fan is actually the best and is ine of the biggest benefits of using explorer serp set up. But that's a lot to change at this point.

By the way, how hot is "hot" ?

Sorry, me and my acronyms

OEM original equipment manufacture

Our Broncos originally came with a 7 blade (or was it 8?) fan that had very sturdy steel blades that don't deflect like the ones on the flex fans.

I would really recommend the nose up trick first. If you have a infrared temp gun you could check how accurate the temp gauge is. 210 really ain't that hot.

When it "overheats" is the engine dying on you (vapor lock) or are you simply worried about damaging the engine ?

Also, do you have a functioning expansion tank ? If it is getting hot enough to puke fluid you want to catch that in the expansion tank so it can get sucked back into the radiator when the engine cools down

If the nose up trick doesn't work I'd invest in a new radiator or a thorough cleaning of your existing one by a radiator shop. The fan may help, but a new radiator solved a similar problem in my truck.

What year did you get the water pump for. If you got it the year of your bronco then you should be fine. Also like Rox asked are you sure the temp gauge is working correctly . Wish you all the luck

210 isnt hot by anymeans. Most newer cars run at 210-220. Manufacturers found that the warmer an engine runs the more complete the combustion process is. Rox is leading you in the right direction. What temp t-stat did you get? You may have a cavitated pump. Or an air bubble at the temp sensor. I'd start by trying to burb the system and just let it run. If it gets to 230 then shut it down. One other thing to try is let the garden hose run across the radiator to see if that helps cool it off.

We may have just found your problem.

OEM stat was 185 and 5.0 went to 195.

With yours being so low, you might not be holding I. In the radiator long enough for it to cool it down

In other words, the stat is always open and the coolant is continuously circulating.

I would try a 195 with the weep hole

I replaced thermostat and did nose up trick.

It WORKED thank you thank you thank you thank you
it fixed it and now runs 190-200 tops thanks again for all the help
you guys R awesome

Glad to hear. Its nice when its a simple fix.

Flex fans aren't great for cooling a slow moving vehicle. They are made to flatten out at high engine rpm. Most cars are moving down the road with high rpms, and air is being forced through the radiator. When we are running trails or crawling, our rpms may be high but we are going SLOW, so there is less air pushing through the rad.

A fixed blade fan would be better, and available through any regular Bronco vendor.

A few years ago when I swapped to EFI, I added a clutch fan. I kept v-belts/standard rotation, so I used this set up:

http://classicbroncos.com/forums/showthread.php?t=81601

Its been a good set up.