Maybe their temperature gauge is not telling them the truth. Most cars have had their temperature sending unit replaced with a GM/Delco or an auto part's store replacement temperature sending unit. This may be their problem!
GM/Delco and auto part's stores can sell you a replacement temperature sending unit, but those do not produce accurate gauge readings in vintage cars. They are only a generic replacement; often requiring a new, matching gauge or re-calibration of your original gauge.
Months of research were devoted to this project in order to provide our customers with sending units that have the correct terminal connection, correct, housing and correct resistance (thermistor) resulting in an accurate gauge reading. Made in U.S.A.