I got a 75 ford truck 400 big block..temp guage stop working , and the thermostat went bad...?

Question

a day apart. well anyway ..i got it home carfully..well i changed the thermostat..and the engine ran fine..plus i put a live gauge in for the temp...today the motor was starting to knock bad...like a jack hammer was under the hood...lost compression...and my temp was rising also...have i messed up the motor...have i throwed a rod..please inform me

Answer 1

Bet you wished you bought a Chevy huh?

Answer 2

You've cooked it probably not a broken rod .

The bearings are stuffed the piston and rings scuffed and its time for a rebuild or a crate motor.

When ever the engine temp goes over  210 deg F pull over and let it cool down.

Also if the temp suddenly goes from normal to cold it could be a busted hose pull over check hoses.

Answer 3

It sounds like you've smoked the engine.

Usually, when an engine overheats and is kept operating for any

amount of time after that, the piston rings and the piston rod

bearings are the first to go. After that, the crankshaft bearings

are next and the engine will seize.

If you've lost compression, you can attribute that to the piston

rings having lost their tension. You may also have blown the cylinder head gaskets a/o the cylinder heads themselves got warped.

Consider the cost of getting a rebuilt long block vs rebuilding

the one you have.

In the future, if you experience an engine from this era over-

heating, don't only look for the obvious...low coolant level,

stuck thermostat, blown hoses.... take a good close look

at the cooling fan clutch as well! It should stop spining with-

in seconds after engine shut-off. If the fan continues to spin

freely, replace the clutch or better yet, see if you can find

an earlier model of the engine type with a mechanical fan.

Good luck to you.

Answer 4

if you lost compression, it sounds like the valves. i had a 74 ford truck once with a 302 and i had trouble with keeping the rockers tight. maybe 1 of the rockers came loose. pull the valve pans and check the rockers out.

Answer 5

Any time you let an engine overheat, there is a good chance that you killed it.  You should always shut down an overheating engine immediately.

Answer 6

I don't think you've lost a rod. If you had, the motor would not turn over.

The loss of compression is serious. It's a block strip down for sure. A knock that sounds like a jack-hammer could be collapsed lifters (hydraulic).

If it's a deep thud that sounds like it's coming from the lower portion of the block, it's probably big ends or mains.