2150
« on: July 14, 2019, 11:15:56 PM »
Can the OP please let us know if the engine has been over-bored...and if so, by how much?
A 0.060 over 289 (and a lot of other engines) will tend to run hot, IMO. Early Mustangs weren't exactly known for having lots of thermal reserve in their cooling systems, although YES millions of early Mustangs have run just fine with all the stock equipment. But now we have here a rebuilt engine with unknown specs, an alternate coolant, and possibly other things that might be contributing to the "running hot" issue. (I'm still suspecting a vacuum leak and/or the retarded timing...OR the simplest answer in that there's nothing wrong at all. Once the coolant level and any air pockets in the system have been worked out, it may operate properly.)
I agree with Doug and others who have said that 200-210 is not hot. You need a lengthy 212-degree heat to burn off condensation. That's why, long ago, many little old lady cars had tons of gunk in the crankcase despite having only a few thousand miles on the engine. They weren't driven long enough to get "good and hot" and thus that became a great contributor to the sludge. Fortunately, oils have improved markedly over the decades, but it still is a good idea to not over-cool the engine so far so that it never gets up to "proper" operating temp.
As for the thermostat temp, I tend to agree with running a 180-190 t-stat. But I have also owned cars that ran hot and I removed the t-stat completely. Some still ran hot, while others ran a bit cooler. In those that ran cooler, it probably was a malfunctioning t-stat in the first place, so removing it helped the coolant flow. The primary purpose of the t-stat is to allow the engine to get up to operating temp. Most notably in cold weather. Once the t-stat opens completely, it's up to the rest of the cooling system to do its job.
Bob has seen/judged/scrutinized more Mustangs than I have, so I will defer to him as to a (relatively rare) situation where a lower temp t-stat actually does reduce overall engine temps.