v8 flathead temp. gauge goes up and down

Might it help if you drilled a small "bypass" hole in the thermostat? Seems to me that if the thermostat is located any distance from the heat producing parts of the engine, there will be a slug of cold water that hasn't been heated right behind the thermostat and it won't open until that slug has gotten up to engine temp. Once the thermostat opens, all the hot water in the engine will rush into the radiator and cold water from the radiator will rush into the engine all the way to the thermostat which will promptly close. Then the whole cycle will repeat itself. Having a small bypass hole in the thermostat will allow a small amount of water to circulate and the thermostat will open sooner possibly eliminating that kind of cycling. Make sense??
 
I got my replacement single pole sensor today and will try to install it tomorrow. I will take new lazor readings and also see what the dash gauge reads. I think my last lazor readings were 164 on one side and 185 on the other when the gauge was bouncing up and down. That was with the t-stats in. I must apolagise for how long it takes me to reply. My two sisters and I take turns babysitting my 99 year old mother. I have been retired for 10 years and I still don't. have any time. I know that you guys will help me solve my gauge reading problems. Thanks Rich
 
OK-- I put the new single pole sending unit in and so far all seems to be ok at idel in the driveway. No time to take it for a ride. I had a flat tire and I had to order a new inner tube. I have the truck up on jack stands. Tomorrow I will be babysitting my mom. Later Rich
 
FROG_PONDS said:
OK-- I put the new single pole sending unit in and so far all seems to be ok at idel in the driveway. No time to take it for a ride. I had a flat tire and I had to order a new inner tube. I have the truck up on jack stands. Tomorrow I will be babysitting my mom. Later Rich
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Every time you make a change it's IMPORTANT to take the laser readings
at the same spot on both heads. This will show if any improvement takes
place. G.M.
 
OK--The tube came in and I fixed the flat. I was able to take a ride in the truck and this is how it went.(I did not drill holes in the thermostats.) The temp gauge did not bounce up and down this time but the gauge went up to 3/4 and stayed there the whole ride.It was 75 degrees at the time I went for my ride. After that the lazor indicated 185 on drivers side at the head outlet and 180 on the passenger side.
 
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