TOO HOT FOR WHAT? Should be the question. There's efficiency issues, hot, then there is hot-hot until I worry about damage, HOT!
Today's cars are designed for higher temperatures due to the emission issues, lubricant operating ranges and generally the WHOLE system is designed to run in a higher range. The emission side dictates certain tailpipe emissions that have to have hotter engine temperatures and work very efficiently there.
Yesterday's technology does not like to work in the over 200 catagory for efficiency issues due to the whole engine block and heads are designed with differing cooling capacities and flows (making for different peak combustion temperatures), plus clearances are different also. From a practical standpoint, the older technology etal likes 175 to 195 temperature ranges (actual coolant temperatures..remember, you can taint temperature readings on the heads by sensing temperaturet there...hotter).
Today's lubricants are a leap in technology with respect to temperature range and really like 175 or above for proper lubricating properties. I would highly suggest for those of you out there that are running synthetic oils to get your temps up in the 185 range for best oil performance. 160 is too low, optimumly speaking. It won't hurt anyting, but you may be losing some lubrication qualities at that temperature.
Okay...on to the what's too hot for damage. As one poster brilliantly pointed out, as long as you are NOT losing coolant and are stabilized, don't fret! GM specs in the 60s called for ranges as high as 235 degrees operating range. I have seen many a cooling system show 240 accurately, holding coolant, and have no ill affects for years!...oh yeah...with aluminum heads too.
So, the key is accurate sensing, holding the coolant, and about 240ish and stable in my book. If it keeps going...then something is amiss. And, actually, you can be losing coolant at an indicated 200 and have hot spots occuring internally due to trapped air, insufficient flow, low pressure etc. that are far more potentially damaging than just 250 degrees!
Did I make sense?
ps....don't confuse engine operating temperatures with the old "to make hp you have to make heat" thing. Yes, hp requires heat in terms of peak combustion temperatures, but these combustion temperatures don't necessarily translate to engine operating temps. It's far more complicated than that!
ConceptOne Pulleys and Brackets
Northern/Southern Rodder Magazine's "Jack'Stands" author and creator
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