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Discussion Starter #1 (Edited by Moderator)
Alright here goes:
Bought the truck about three weeks ago, drove 2h45 the night of purchase - never went above 58mph, temp gauge never rose above 140F. I've driven the truck a good few times about ten miles one way and the temp never rose above 140F. Yesterday I took the truck on an hour long trip to a welder to fix a bad spot on the frame - after a completely cold start I was feeling confident and cruised about 75 for about ten miles, then 60 up a rather steep bridge. As I was coming to the apex of the bridge, I noticed the temp gauge start to climb. It hit somewhere between 230 and 240F as I hit the decline, then I took the exit immediately after the bridge. Well, the next section of road is set at 45 mph, so I abided. Temp lowered to 200. Next section of road is 25mph, but the guy in front of me was only doing 15. At this point the temp rose to 220 and stayed, and I started to hear a knocking sound, but not a knock that suggests a bent rod. I continued to travel down the road where the speed limit increases to 40mph after a couple miles, then the temp rose to 240. Feeling uncomfortable, I pulled over to let it cool down. Steam was billowing from the radiator cap and there was smoke off the passenger side exhaust manifold (given that I could smell oil burning during this return trip, I assume the valve cover leaks badly enough to reach the exhaust manifold and with coolant pressure being high enough to steam out the rad cap, it may well have reached the exhaust manifold as well)
Anywho, after sitting for half an hour or so, I checked the reservoir tank, and since it was a third of the way full, foolishly assumed there was coolant in the radiator.
I made it three more blocks before it hit 240 again.
My first assumption was that the thermostat locked up so I replaced it in a parking lot this morning.
I loaded it up with coolant and drove home with only one incidence of strangeness - but that may well belong in another thread.
The odd thing here is that the temp gauge did not read at ALL on the way home and the radiator had maybe a quart of water in it when I drained it.
I have since pulled upper and lower hoses (lower hose spring rusted and crunchy), checked water pump for slack, ran water thru all radiator outlets (plenty of flow) - I also pulled the heater core line off the radiator and pushed water thru the block and out of the water pump. Therefore I find there is flow in the right places. There is zero milkiness to the oil on the dipstick.
Something I feel is worth noting - when it ran hot, the upper hose was **** hot but had very little resistance to being squeezed, while the bottom was reasonably hot and had pressure to it.
Does this sound like an intake manifold gasket leak?
 

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time to get cereal
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You were low on coolant the whole time, the reason you were reading 140 is because the temp gauge was reading air and not coolant. Either lower intake manifold or head gasket(s). Adding coolant doesn't get rid of the air in the system.
 
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