Weird Cooling Problem

[another69]

I have a SBC with Dart aluminum heads, an electric fan, and aluminum radiator. Pump speed is 1:1 to engine speed. 160 deg. thermostat, fan comes on at 185. When it is above 60 deg. outside the cooling system works great, no issues, very consistent temps, never gets above 190. I have two temperature sensors on the motor, both in the intake right before the thermostat. One on the driver's side, the other on the passenger. When it is cold out (took it out yesterday, about 50 deg. outside), the passenger side will take awhile to warm up, but cycles the fan as it should. The drivers side will run warmer and will get all the way up to 250 (!) then drop to 180 within a minute or so. This happens over and over again. I think it is the thermostat cycling, and the faster the car is moving the worse it is. Passenger side stays about 160 - 180. I think for whatever reason the water flow is really not as balanced as it should be side- side or there is a thermostat issue. This only happens when it is cold out, but it happens EVERY time it is cold out.

[dirty rick]

No thermostat bypass? There has to be a passage for coolant flow when the thermostat is closed. This circulates coolant in the motor and prevents hot spots while bringing coolant by the thermostat so it can see the actual temp. Often the bypass is via the heater circuit.

[another69]

It's a Gen 1 SBC, so as far as I know it does not need an external bypass. The problem only happens when it is cold out and the car is moving. I'm pretty sure that the t-stat in the motor has the 1/8" bleed holes. The only thing I can come up with is that the cold water is flowing through the radiator, into the pump, and flows through the passenger side, then through the bleed holes which is keeping the stat closed and the other side of the motor hot. Once the stat opens all is well, then it cools down again and shuts (over and over and over). Maybe a standard stat will do the trick?

[red67camaro]

On a Gen 1 sbc, the thermostat bypass is an internal passage that runs from the passenger side block deck to the intake side of the water pump resulting in more water flow through that side when the thermostat is closed. It's the reason for the extra hole in the water pump mounting flange on that side. I would think that any flow through the drivers side would be from whatever mixing that might occur in the water pump and/or the manifold crossover. The flow would equalize once the thermostat opens.

A solution? I don't know. This is the first time I've heard of someone gauging each side separately.

[GEARBOXGARAGE]

As mentioned above, each side should be fed equally through the factory design of the water pump mounting flanges, unless there is some unforeseen blockage that you are unaware of. Try swapping the sending units from side to side. If the same scenario follows the sending unit to the other side, I would say it is the sending unit that is bad. Are you going by gauges only or can you tell a significant difference in temp from each side under the hood?

[dirty rick]

Many water pumps don't have a passage for the bypass hole. Some blocks have a plug in the hole.