so based on all the feedback I received I did a few things to check the status of my radiator:

1) I looked at the water/coolant inside and it was mainly clear water...I hadn't added coolant in a while but it was clear....not dirty or mushy....
2) I felt around the radiator to see if I could find 'cold spots'..... I didn't feel any
3) I flushed the radiator and filled it with 50/50 new coolant mix
3) I replaced the thermostat about 6 months ago and the viscous fan about a year.....so those should be good

Today I drove about 40 miles with steep inclines. And half way through the temperature gauge went to the highest point in the normal range ( not redline) as I was going up....when I came down on the decline the temp gauge went back to the mid point....this happened a few times during the whole trip.

Does anyone recognize these symptoms? What does this mean? My truck never did this before...the temp gauge was always leveled.

Doogaloo

 

You need a real temp gauge, not the junk one in the dash.

 

First, never run tap water or you will build up calcium in the veins .
As for the hot temp, that will kill your engine, it will cause the glue on your sleeves to fail, so stop driving it, have it flushed out and only used distilled and coolant, no tap water.

 

Really? Should I pour some more Elmer's Glue in with my next oil change?

 

Tom R, looks like head gaskets at this point. I took the disco to 2 radiator shops and both said cooling system was fine...must be the engine. If I'm going to replace the head gaskets, then I'm going to replace most of the ones I can including getting the heads done.

I wonder, if I take it that far should I just change the lifters and push rods too? I don't have cherry picker so I can't take the engine off and I doubt the engine has ever been overhauled...so I just want to improve the best I can for now...it's a 98 DISCO....ANY SUGGESTIONS?

 

Here's what I noticed. My 98 D1 is fine normally. However, on days when it's 100 or over the temp gauge goes up a lot, especially going uphill at highway speeds. I replaced the radiator and the fan clutch to be safe.

What I noticed when burping the new radiator with the plug out is that with the old radiator you didn't see much if any circulation. With the new one with the plug out I could see a lot of circulation. An amazing difference.

The day I replaced the radiator it happened to be 105-106 out. I drove it after replacing the radiator at 70-80 and up a steep grade on the freeway twice with my foot in the radiator and in 3rd gear and there was no overheating whatsoever.

Based upon this I'd make an educated guess that if you have overheating problems you should pull the top plug on the radiator and see if there's circulation. If not, your radiator is probably plugged up.