Thx for ur answers Ordieh and Doc Olds. No, the temperature didn't get to the 3/4 mark. I panicked and turned off the A/C prior to that. lol. Will check for the seal above the radiator and the fan clutch. I didn't know the H3 had all those overheating protection mechanisms: cool.

Any explanation as to why the ambient air temp readings went up as well?

My check engine light came on this morning, so I will have to take the truck into the dealer for a checkup.

The dealer is THE last place on earth I would ever take a vehicle for a CEL.. Take it to an auto supply and have them scan it for you, could be easy DYI fix.

One thing about a dealer is that they will tell you everything that's wrong, even imaginary things, lol. Anyhow, I was referred to a well respected private shop, so I am taking the Alpha there this Wednesday for an assessment. Will let you know what he finds. My check engine light is on, as is the "low tire pressure" warning.

Nice info on the foam seal. Redline also has a product to hep with the coolant cooling better: https://www.redlineoil.com/waterwetter They say u can use just the 12oz waterwetter with straight water (distilled?). Im thinking of doing this for the summer months.

I think I've seen/heard at least as many stories of H3 CSF radiator failures as I have of OEM H3 radiator failures, although I will admit that the CSF failures haven't typically resulted in a mixing of the fluids (that I've heard of anyway). Of course, neither have the majority of the OEM failures, either. My radiator failed just about a month and a half ago; split top tank, no fluid mix. I've got 145K miles, went with an OEM replacement.

Just to be clear, you didn't replace the OEM factory installed 25964054! My oem only lasted just over 5yrs(many others less). However, my $110.66, 8yr old, 9589A Silla, replacement is still sealed tight and haven't lost a drop of coolant. I did however make a mod to the upper mount: H3 Radiator

Actually, I did. This one. I had no confidence in any of the aftermarket radiators, especially the aluminum ones, so OEM was important to me. With the whole COVID thing going on, this was about the only OEM one I found at a (relatively) reasonable price that I could get in a short amount of time (3 days from order to delivery); I needed it back on the road asap.

BTW, the mods you made were unnecessary on mine; there is less than 1/8" (at most) movement within the top mount, and the metal crossmember does not touch the radiator. Even the old (cracked) one shows absolutely no evidence of ever touching. I made sure to double check that after seeing lots of reports on it. In any case,the original lasted for 12 years and 145,000 miles...I think I'll take my chances on another.

How long have you owned your H3? :confused:
My mod was on the upper mount, to prevent any movement/flex which caused the stress crack on the upper tank. With the insert, there is no movement, and outlasted the OEM.

I've had it for 5 years now, put 55K on it during that time. The new OEM radiator matched the old one exactly, right down to the numbers and stampings; no reason to believe that it wasn't the original radiator. CarFax didn't reflect anything when I bought it, although that really isn't saying much. However, while there have been plenty of failures, the majority of H3 radiators have not failed. Of course, no one goes online and complains about a "non-failure", so...

I saw your mod; there is so little movement in mine that I don't think I could even fit a sleeve in there like you installed. Maybe your rubber mount was worn? The little bit of movement in mine is strictly the "give" of the rubber. My bracket also appears to be slightly "flatter" than yours; perhaps shifting the radiator a bit farther away from the metal cross member. Or maybe the V8 is slightly different?