Question

[MikeCS1]

Question: What is the proper Operating Temperature Range (In Degrees) for a Buick 350 c.i.d. engine (With automatic, and A/C) made from 1971 to 1978? I was told by a mechanic that 200f is ideal, "but the more you see the temperature guage progress above that, it means something is wrong and it is getting too hot"...However, he's also told me things that I already know are wrong, such as: "In 1971, these cars did not use Multi-viscosity oil, so use only 30W."

[The Old Guy]

If you run a 50/50 mixture of water and antifreeze, you can run it to 230-240 degrees and never hurt it. My 455 occasionaly sees 240-250 and it still runs just fine. The only time you have a heating problem is when you start loosing liquids. if the rad is in good shape ,and the cap is doing its job , you should not worry about a temperature spike. If the engine runs continuoslly hot, then start to worry

[MikeCS1]

I appreciate "The Old Guy" responding, but my question actually remains unanswered. "What is the Proper Operating Temperature Range (in Degrees) for a Buick 350c.i.d. engine (With Automatic, and A/C) made from 1971 to 1978? I've already checked my "1971 Buick Chassis Service Manual, All Series", but the only things I've found where it even mentions any numbers are as follows: "The thermostat valve opens at 190 degrees F." (Which still applies to mine), and "Engine water temperature above 246 degrees causes the set of contacts to close and light a red signal on the instrument panel.", and "If engine temperature should go above 265 degrees plus or minus 10 degrees'...[Everybody notice that means anywhere between 255 and 275 degrees]...'a set of contacts are closed and lights a red "stop engine" signal on the instrument panel." (Those last two entries in the manual may not apply to mine, since it has guages installed). Of course we could therefor assume that the Proper Operating Temperature Range is anything below 246 degrees, but it's like the wise man once said "Man who assume wrong will wish he had'nt". So again: What is the Proper Operating Temperature Range (In Degrees) for a Buick 350c.i.d engine (With Automatic, and A/C) made from 1971 to 1978?

[Smartin]

Ideal operating temps are around the 180-210 area.

[NTX5467]

In reality, it sounds to me like your mechanic is giving you good information. If you read the owner's manual, 30 weight oil is fine if the normal temperature range is above 32 degree F. Multi-viscosity 10W-30 is fine for that temperature range too. Consider, too, that many 10W-30 rated oils of that general time frame "lost" some of their viscosity rating, with the oil that started at 10W-30 could end up as 10W-20 after a period of time (due to degradation of the additive package that gave it the multi-viscosity characteristic). Straight-weight oils did not have that "instability" and usually stayed "in grade" longer, unless diluted with fuel from poor ring seal and such.

In some cases, oil consumption was also greater with multi-vis oils back then. If an engine had begun to "use" oil, sometimes the straight-weight 30W oil would cure it, or at least lessen it. In other words, multi-viscosity oils in the earlier 1970s were technologically advanced, but still had some issues in some engines. The basic default mode was the straight-weight oil over a multi-vis oil.

Also consider that not all engines were built to the same exacting tolerances. Not that they were "thrown together", but that in some cases there could be some that were closer to the design specs than others. For example, a valve guide could have a +/- spec in sizing, just as the valve stem would, which could result in being "in spec" for each part but a little "different" when the two were assembled. One reason why there could be a 20 horsepower (or so) variation between engines built on the same day on the same assembly line by the same employees as EVERY machined/cast part of the engine could have the same "build tolerance buildup" of the + and - specs to influence the final product. As good as they were, quality control is better now than then.

The early 1970s also saw the introduction of the "super oils" of 10W-50 ratings to compliment the existing 10W-40 oils. An oil to handle the extremes of engine operating temperatures and ambient temperatures for a vehicular society that could travel to completely different climates in a few hours, without having to change motor oils to compensate.

As for the engine's operating temperature, remember that the temperature stated in the thermostat's spec is "openning temperature", not "full open" temperature. With the 1971 GM engines (and many others, too) now specifying a 195 degree F coolant thermostat for emissions purposes, a 200 degree temp operating temperature, or even a 210 degree temp in some cases, would be acceptable. I concur that if the temperature starts increasing much above that, something needs attention under the hood (fan clutch, coolant level, radiator internal restriction, radiator fin clogging (external), radiator air baffling "gone", ignition timing or similar)--especially at highway speed. I also concur with Adam's comment of "operating range".

The service manual comments for the warning light orchestration can also be a good guide to consider. Plus that ATF used to begin to deteriorate from heat at 270 degrees F. But as you have gauges, you should be able to tell where your engine is currently "running" in the temperature situation. Generally, mid-gauge is good, hopefully toward the lower side of that range. On my '77 Camaro, 210 is the middle point, and the needle ususally stayed about 1 needle-width below that with the stock 195 thermostat. Above about 210 degrees, you should hear the thermostatic fan clutch start to kick in.

Just some thoughts,

NTX5467

[MikeCS1]

Adam, thank you for your response.

[MikeCS1]

NTX5467

Thank you very much for your answers.