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2wo minutes??????? That's a bad gauge or sending unit.

I agree with PV8. You need to rule out a couple of things in that circuit.

If you have an ohm meter, check resistance of sender to ground. With wire disconnected and engine cold, you should read 80-100 ohms. With engine at normal temp, should be somewhere in middle of range. I'd guess around 30-40 ohms. Anything less and the sender is suspect or someone put the wrong sender in. Obviously, with the wire disconnected the gauge should be on cold. If anything other, then need to look for a problem with wiring.

If it pegged, you should have been dumping some coolant out on the ground. Any boiling over?

Also, if you use too much thread sealant on the sending unit, i've been told that can be an issue if it's not getting a good ground. Usually not a problem, but something to think about.

And of course, if you have multiple sending units around, be sure and use the right year. 51 and later is different.

It is boiling over,only water in it now to check it. Oil pressure is 25 lbs when idle. I am looking at the heat riser now to see if it is open.

Don't believe a stuck heat riser valve would cause it to boil in 2 minutes. Have you verified any presence of combustion products in coolant?

Also are you sure you fan belt is slipping and you have the correct fan installed? It shouldnt be overheating in two minutes even if the heat riser is stuck.

If it isnt a blown head gasket, then the other thing I could think of that would cause a rapid heat up would be a restricted or partially blocked exhaust system.

Ouch on combustibles in fluid! I hope not.

Kev gives some good advice, if you haven't already I'd take compression measurements just to insure you don't have a blown headgasket. Lots of cars running around with heat riser valves stuck closed, they probably have lots of other problem like vapor lock and the like, but not necessarily overheating. I find it hard to believe an engine could get to boiling in 2 minutes or less; I tend to think that even if you took the fan belt completely off that wouldn't occur.

Quote:
"It is boiling over,only water in it now to check it."

U indicate and i quote "boiling".
That is nearly impossible with in 2wo minutes. Is the water actualy boiling as in more than 212 F or is it just pouring out???? And out of WHAT??? After ONLY 2wo minutes the cylinder head should be only warm or maybe somewhat hot to the touch (altho my hands are pretty tuff). Therefore not overheating.

The problem sounds more like a very plugged up radiator that is not allowing the water to pass thru it.

Possible combustion chamber leak into coolant as indicated above.

Sorry got the sequence wrong. Gauge pegs in two minutes, head gets to hot to touch in about five minutes, radiator gets to hot to touch shortly thereafter, loosend the cap with overflow at about 7 minutes.