Re: Temperature gauge fluctuations on 34 1103 super 8

Posted by Owen_Dyneto On 2009/5/19 8:18:15

You didn't mention any observations about the operation of the radiator shutters which control the temperature by controlling the airflow thru the radiator core. Erratic shutter performance could cause the situation you describe.

The thermostat is a nominal 160 degree unit because alcohol antifreeze was the dominant material of the era and can boil off at higher temperature. The shutters should begin to open at about 155 to 160 and be fully open by 165 degrees. If the thermostat and shutters are not operating freely and correctly, you'll never have good temperature control.

Typically these cars run at the thermostat rated temperature even on quite warm days when idling and driving at moderate speeds; it's not uncommon for the cars to run a bit warmer at higher speeds due in part to the (numerically) high rear axle ratio which gives high engine rpm. But then returning to 25-45 mph the temperature should again return to or near the thermostat rating.

Yes, if all is operating correctly you'll see a bit of cycling of the temperature as the shutters open fully and begin to retract as the engine temperature drops. But a swing to 200 degrees shouldn't occur except in the most extreme of conditions, like stuck in traffic on a 110 degree day for an hour or more. July is typically a very hot month here, and I've crawled along, stop and go, in parades on July 4th and the temperature may gradually creep to 170 or 180, but within minutes of getting back on the road, the temp drops rapidly back to the normal 160.

If you're in doubt about the thermostat operation, disconnect the thermostat linkage and use a small block of wood or otherwise block the shutters wide open. If you then experience overheating, your problem is more than likely with the engine cooling system, e.g. radiator, water pump, fan belts, collapsing hose, water distribution tube, or related items. I hope you haven't blocked off the water flow to the oil cooler; in order for the coolant to get to the rear of the distribution tube and engine it must pass thru the cooler unless the internal baffles have been altered.

Let us know about the shutter operation and we can go from there.

EDIT - Terry, a couple of other thoughts. Since these cars do not use a conventional thermostat which interrupts the water flow, the temperature in the top radiator tank should be within a few degrees of the gauge reading - get a good laboratory thermometer and check to see that the gauge is accurate. If not, you might consider removing the bulb in the rear of the head to insure that it's not imbedded in crud or otherwise not in the path of the coolant or coated with insulating crud. Also, in cool days it's not uncommon for the car to run at less than the thermostat setting due to very cold air getting past the shutters - on winter days mine often runs as cool as 130 or 140. Does you car exhibit this, or does it always exhibit the overtemp excursions even on cool days?