100 degree day, engine idling (after highway speed drive) with A/C on.

Aftermarket, underdash gauge steady at 220.

Actual coolant temp at the top of the radiator is 185.

All good?

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1961 Dodge Lancer

I would have no trouble with that behavior in my car, assuming you are holding pressure in the cooling system and preferably have some (>20%) coolant in the system. Welcome to the site! Where are you located?

Lou

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Home of Slant6-powered fun machines since 1988

located in the primordial swamps of SETX

we'll have 100 degree heat index days until about October

I guess my more specific question is: "Is it an accurate way to determine engine temp by putting a baking thermometer into the coolant at the top of the radiator when the engine is at max operating temp?".

Looks like my aftermarket gauge is reading too high (its sending unit is mounted in the lower side of the block by the oil pressure/oil filter).

Factory gauge looks ok, 185 coolant temp at the top of the radiator.

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1961 Dodge Lancer

I'm amazed you can open the radiator and not douse yourself in boiling coolant, and when you do that you lose pressure. Are you saying you get 220 F on a good quality aftermarket gauge in the drain port of the block? Best to get an IR thermometer "gun" and point it at different points near where the temp sensor is in the head (thermostat housing...), and the lower part of the top of the radiator tank.

Thanks,

Lou

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Home of Slant6-powered fun machines since 1988

I have two temp sensors, one is a FiTech unit in the factory position in the head near the thermostat (I have a 180 degree thermostat) and the other (factory) temp sensor is down by the oil filter where your's is. My FiTech sensor has a digital readout, and I compare that with the old "TEMP" gauge in the dash. The FiTech sensor in the head near the thermostat typically reads 170-80 when driving (at this temperature the factory sensor down by the oil filter gives temp gauge needle pointing to the bottom of the "T" in "TEMP") and in hot traffic 190-210 degrees (while the factory sensor points the needle between the "M" and the "P" in "TEMP"). Not sure if that information helps, but I think the most accurate reading is in the head near the thermostat housing.

I have a '67 dart with a slant six. Air temperature readings in the TBI are 70-90 degrees and 100-115 degrees, respectively.

brian

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https://tinyurl.com/yynpj4v2