1961 1800A gas - cooling - need advice

We have been trying to work the bugs out of the cooling system on this thing and getting a little confused:
1. Thermostat electric sending unit - we replaced it with one the local auto parts store "matched up" but when u turn key on...gauge immediately says hot?
Thinking maybe the positive ground could be an issue? Looking to get original part, but not sure where to get one?
2. Thermostat - we thought we heard water boiling in the engine one day we ran it for a little while...thought thermostat must be stuck...went to take out thermostat and none is in it...looking to buy a new one now...where to get one? Looks like these are big? Brother said it may need one to cool properly?
Appreciate your thoughts.
Reaver

1) Thermistors can have different resistance ranges, but are generally a fairly standard item.

Question is what did it do previously? There can be other reasons for that indication.

2) Generally a thermostat is required to get the engine to run hot under general running conditions. If water was boiling in the engine, there was another reason, not no thermostat. Not a clue as to souce of a suitable 'stat, but an agco dealer might be a good start, or maybe a truck centre, or you local agri-dealer, even.

I would check with Korvis Bros. Waterloo, ILL. They are the "Go To" guys for all things Oliver in the mid west. Good people too. They helped me with my 550.

The temp sending unit/gauge basically did the same thing it is doing now...cold when key off, then goes immediately to hot with key on.
Thanks Reaver

Sounds like no impeller on the water pump... how long did you run it when you say a while? Engines designed with a thermostat is needed for optimal operation in all ranges cold or hot. Korves or napa can help with those parts you seek. Hope this might help. Duane

If it requires a thermostate and there is no thermostat then the engine will over heat. The thermostate does regulate the tempature and it also restricts the coolant flow. With no thermostat the coolant is just being pumped in a continus circle, it is going through the radiator faster than the radiator can cool it. I have seen this happen on an International as well as a John Deere.

Heres an example. My oliver 90 was delivered without provision for a thermostat. It had a radiator blind to regulate the water temperature manually. It was later changed to thermostat (the top water manifold was changed, and I still have it).

Heres another. I wondered why may car heater was cold one morning and the engine was running better with the choke in operation. Thermostat was stuck wide open.

Heres another. Most early iron only used thermosyphon as a means of cooling, no pump and no thermostat.

All those examples did not reach proper operating temperature without the thermostat (bar the ollie 90 with the blind well adjusted).

As to the thermistor problem, you likely have a short to earth in the wiring from the guage to the thermistor.

Typically the coolant temp sensor is a variable resistor, as the temp decreases the resistance of the sensor will increase. For example, I am looking at one for a motorcycle I checked several days ago, at 212 F the resistance is 32 ohms, 180 F is 53 ohms, 140 F is 108 ohms and 86 F is 350 ohms. It is easy to check by placing the sensor in a cup of hot water and reading the resistance as it cools.

The sensor calibration (ohms versus temp) has to match that of your temp gage for the system to read correctly. As you can see there is a big change in resistance and for the gage to read full hot at ambient temp suggests another problem.

1) Perhaps your sensor is faulty i.e. grounded (zero ohms).
2) Perhaps there is a resistor used (now missing) to drop the voltage supply to the temp gage. Some times a voltage regulator is used.

As to the thermostat, if the engine was designed for one I always believe it should not be removed. The thermostat holds a backpressure on the system and can also help control/prevent pump cavitation. I have however, never understood how the flow can be too fast through the radiator such that there is not time to cool the water. The radiator is always filled with water and the is no difference in the time the radiator has to cool it regardless of the flow rate.

Your motorcycle may have a resistor but not a variable one, mind. What you are describing is a thermistor.

However most automotive applications use a thermistor in which the temperature coefficient is negative with respect to temperature. Resistors, per se, have a positive coeffient wrt temperature. However a thermistor could be referred to as a negative temperature coefficent resistor, but thermistor is so much less of a mouthful.

The simple check is to short the meter-to-thermistor wire to earth - the gauge will peg on full scale. When cold the thermistor will be high reistance and the current through the meter a minimum value.

The voltage regulators for the guage supply are almost bullet proof and they regulate at 10.5 volts, so the meter would still not peg full-scale at cold, even if the full battery voltage was applied - the readings would be wrong, but that is all. Thermistors rarely fail totally.

As to the fallacy that no thermostat always leads to overheating, think upon this. When the thermostat is hot it will open virtually fully so as not to unecessarily impede water flow through the radiator - just as though it was not there...