I am sure hoping that someone can give some advice on this. Not real sure where to go next. I have a 1994 Discovery that just recently started overheating. I noticed that it was running hotter than usual one day but never got real hot. Then driving in town one day it climbed up to the top white line before I got it home. I let it cool off and checked the coolant. Full and looked great. I went ahead and put a new thermostat and resevoir cap on it. Started it up and let it run in the driveway for an hour. No problems. Gauge sat at about 9 o'clock and looked good. Started to drive it and within 5 minutes of in town driving it got hot again. Took it home and flushed the radiator out. Got in it and headed out of town. Drove about 15 miles to a restaurant and it did great. Left there after an hour to return home and five miles into the trip it started to get hot again. Let it cool. Check the coolant level and it was full. Pulled the radiator plug and ran it thinking I might have air in the system. Ran for 20 minutes until I was getting steady fluid from the hole and put the plug back in. Still having the same problem. Oil looks good with no coolant in it. No unusual odor to exhaust. Any ideas of what to try next? Fans appear to be working fine and saw good flow in the radiator with the plug out.

Thanks for any help.

 

Get the radiator rodded out. Probably partial blockage.

 

Check radiator fins temperature top to bottom. With IR thermometer or Mark I palm reader. It is a horizontal row radiator, so sludge closes off the bottom rows first, if bottom area cooler by 10F or more blockage has started. You are so lucky because radiator comes out easy, and a small indy rad shop can un-solder the side tank and rod it out, usually under $100. On a $700 radiator. Aluminum w/ plastic tank aftrer market available for $235.

Check viscous fan clutch, when hot, engine off, spin and release, should come to a stop in less than one turn. If it freewheels, the fluid inside is with Elvis (left da buildin). New clutch is $60 is, Chevy 2000 Express 4.3 liter, w/o AC. You'll have to enlarge fan mount holes in the fan.

Don't drive with it hot or above normal.

 

9:00 on the temp gauge can be anywhere from 180-230 deg, so it's not a very accurate way to determine your engine temps. Ultragauge is well worth the investment. (About $60.)
The fact that it gradually got hotter seems like a fan clutch / water pump problem. Radiators don't usually suddenly start to clog up, but it is a possibility. (Unless you put stop leak in them.) Occasionally you can get a bad thermostat right out of the box. Lots of people test them in a pot of boiling water first. Cracked blocks usually have other symptoms. (White smoke, milky gunk in the oil, waterfall sound in the dashboard, etc.)

 

For what it's worth, you could expect good flow through a partially blocked radiator and a flush is pretty much useless. Do this; start with a cold truck, run it until the thermostat begins to allow water flow. Don't run it long, just enough for the radiator to start to show a slight warming trend. Switch off, feel radiator on fan side, top to bottom. They should feel exactly the same temp. If you feel warmth up high and ambient down low, you have a clogged radiator that needs rodding, period. Mine was 60% blocked, mechanic had told me not to worry because it had good flow. This is a handy procedure if you don't have a laser available and is performed before the radiator gets too hot for your hand to even feel a difference of 10 degrees in temperature. Best of luck!

 

I had the same problem in my Bmw when the water pump impellers broke.

 

yes, but in a D1 that is pushing 20 years old, the corrosion inside the water pump may be holding it together. And if it was slipping, rolling down the highway would overheat as well. You can take out that radiator vent plug and shine a light down the edge of the ends of tubing inside, I could see white on mine from calcium. Water pumps tend to wobble pulley when ready to jump off the cliff with the fan clutch. Of course it is a $3 gasket to inspect what you have. Note that a D1 and D2 pump are the same, in case boneyard nearby.