Question for the crew on engine temp

Does it matter (other than faster warmups for the heater) to have the engine running "cool"? Mine ran between the M and A before I swapped out the leaking radiator for a new one. Since I did that it runs between the N and O during the summer (Texas) with the AC on and I noticed today that it was just before the N but still inside the NORMAL "bracket" (55 degrees out today with no AC/no heat on).

For kicks I bought one of those Tempature Radiator caps (gauge built into the cap) a while back just to verifiy what I see in the dash. It matched - engine was "just in" the normal operating range.

Is that a bad thing?

 

The OEM gauges are notorious for giving owners conniption fits due to their inaccuracy. Aftermarket oil pressure, water temp and volt gauges with the numbers are more accurate.

Ideal operating temps for the 351M/400s are 190 - 210 degrees, F. Hard to tell where that fits on the "NORMAL" range. When my aftermarket water temp gauge reads 190* F, the T-stat opens and gets down to 160* F. Climbs up, goes down, etc, and stays around 190* F or less in these colder months.

Hope you have the correct thermostat for your 400....

 

Mine reads just below where the normal range starts, and the heat doesn't work well. Thinking it's the thermostat so I replaced it today. We will see how it does tomorrow

 

It's important for any engine to reach normal operating temperature as quickly as possible. The heat is nice, too, but from an engineering standpoint it is important even in the summer. The idea is to prevent engine sludge buildup, maximize fuel economy and minimize pollution. Piston cylinder wear was found to be cut in half by manufacturers going to a 180 degree thermostat versus a 160.

 

Temperature - accurately measured - does matter. Cold cylinder walls tend to condense fuel and wash the oil off. Adequate temperature helps prevent this and can increase engine life.

The factory temperature of around 195 F is probably ideal. 180 degrees OK. Cooler than that may shorten engine life a good bit.

Of course too hot is no good either. It promotes pinging and failure of the cylinder head.

The stock gauge is not particularly accurate or consistent from truck to truck.... I wouldn't (and don't) worry about slight variation after changing cooling parts especially if it is running just a bit cooler. If worried, get an accurate aftermarket gauge to measure.

 

Thanks for the info guys - just what I was looking for. Truck runs in the 180-190 range but I'll keep an eye on it over the winter and if I see much sub-180 than I may replace the thermostat. I see other threads about challenges finding the right one for a 400 so I may be back ! thanks again for the help - FTE always the best place for advice on these dents!

 

Thermostat ratings have generally increased through the years primarily so the manufacturers could more easily meet the MPG & emission goals. The higher temperatures generally provide greater efficiency, but also more tendency to pre-ignition, fuel percolation, lubricant viscosity reduction, and a greater expansion differential between dissimilar metals. My F-250 came with a thermostat marked 178 degrees. I also have a 442 which came with a 180 degree thermostat, and a '62 Rambler which has always run with a 160 degree thermostat. It has almost 400K miles on it without an engine rebuild. It still has ample oil pressure, but is probably operating near or past the specification's outer limits. I have a Chevy parts book which shows a 151 degree thermostat for vehicles from 1933 to 1959. New vehicles tend to be over 200. Ford chose not to assign actual temperatures to the gauges in our trucks. Some other manufacturers have done this also. Perhaps it is due to inaccuracies. The closest they come for my '76 is in the gauge testing procedure where they say that at a measured temperature of 180 degrees the gauge should indicate within the "normal" band. Whoopee! Mine is a 460, but I understand that the 400 takes a special thermostat that has a piece on the bottom to close the bypass. There are discussions on this forum about it. I don't know how many temperatures are available for the special thermostat, but "shop around" and choose carefully.

 

Thanks Ozzie !