How Hot is "Too Hot"

[james singleton]

I have a 66' - 200cid engine with a stock radiator. I am curious, for those of you with temperature gauges, how hot does your vehicle run under normal driving conditions??? What would you consider as "too hot", and at what temperatures would you start getting concerned that either the radiator may be insuffiecient, your timing may be off, etc., etc.?? Thanks for any input! Jim

 

[ludwig]

I knew something was was wrong when I heard a bang-bang-bang while driving. Then when I popped the hood the water was boiling out the overflow. Seemed to me something was wrong.
Got a new radiator cap and a 160* t-stat. Seemed to take care of the problem. On the other hand, I spent a little time making sure the coolant was going all the way through the block. I would run it for a while and then it started to bubble and the level would drop. Topped it back up. When it quit dropping, I put the top back on and it seemed okay. Heater works great too.

I think the 180* was a little hot for LA and a lot of uphill driving.

 

[LincolnMarkVII]

With a 180 T-stat and a worn-out clutch fan, mine creeps well past 190 on a warm day. (which is most of the time down here in Florida) However, I rigged a 16" pusher fan with a relay to a dash switch, and I try not to let it get too far past that. Eventually I'll run a second 16" as a puller and run that off a temperature sensor set to 190-200. The electric fan only cost me about $70, plus the cost of some heavy duty wiring and a relay and a switch.

Sometimes I think there may be some issues with such a long cylinder head and having my (aftermarket) gauge's temperature sensor at the back of the engine. I'd like to have a second sensor up on the thermostat housing.

 

[rbohm]

8) for best wear and mileage, running the engine around 200 degrees is best. ofr best performance running the engine around 175 is best. personally i use a 180 tstat, and when i install an electric fan i will have it come on at 200 degrees and shut off at 175 degrees.

 

[james singleton]

The reason that I asked the question about "what is too hot"?, is that most of the time my temp guage reads between 180 -190*; but a while back when the outside temperature was pushing 90* my temp gauge went a little bit over 200*! I can't remember what degree thermostat I have installed. I have not had any coolant go into my coolant recovery bottle yet; am just curious as to when I should start getting worried that the engine is "too hot"??? @205*?, 210*?, 215*?.....I have been thinking about installing an electric fan; especially since the temperature rises significantly after the engine is shut off, and subsequently is sometimes hard to re-start (due to the fuel line becoming so hot and cooking the gas, I believe?). Thanks, for your input! Jim

 

[ludwig]

That dashboard gauge is just a relative thing. There are more accurate gauges available.

 

[wallaka]

That dashboard gauge is just a relative thing. There are more accurate gauges available.

Pretty much, the only thing the dash gauge is good for is saying: "Heat? Why yes, I do have some." Other than that--useless.

200 degrees is nothing to worry about. Heck, I'd say that 220 or so isn't a cause to worry, as long as it is not constant. If the coolant isn't boiling, you are generally fine. People do freak out about this more than almost anything else for some reason.

 

[BUZZ]

As long as your water doesn't boil out you'll be ok.The biggest danger is over heating an engine and then putting cold water back in.With the proper presure cap and proper amount of antifreeze 220 to 230 is ok.

 

[JackFish]

That dashboard gauge is just a relative thing. There are more accurate gauges available.

Yah, my gauge (Hastings) reads 240 on the highway, I have no leaks, and use a 16lb rad cap. I think the engine does run a bit hotter if you have the cam advanced (mine's 4*). It's never boiled over and I've even pegged the guage. Haven't changed the coolant in three years, it looks good, just top it up now and then. There's a new heater core, though.
Well OK, the original rad does weep a little bit now and then...
Oh yeah, a 195* thermostat.

 

[ludwig]

Other things than ambient outside temperature will cause a hot running condition too. To lean fuel/air mix will overheat, lugging or standing at idle too long.

 

[addo]

I reckon fuel grade seems to make a difference on carbed cars, too. The DD runs on low-octane, but it's more inclined to heat up and start coughing a bit in slow traffic. Perhaps the slower burn of high octane fuels creates a slight cooling effect inside the chambers?

 

[MercuryMarc]

Water boils at 212 degrees at sea level, and under pressure it will boil at a higher temp and with anitfreeze (funny name, huh?) the water boils at an even higher temp. So I have my setup with a 180 T-stat, electric fan on at 210 and off at 185. Got up to 225 uphill over a 8000 foot summit at 75 MPH in 80 degree weather on the way to Reno to Hot August Nights, and the only thing that happened is that I was very nervous. Car ran fine and cooled off when I slowed down to 65 and went downhill.

 

[fordconvert]

I have a car that runs 230-240 most of the time in the summer. Its been like that for years. Modern efi cars stay around 200 year round and get mad if they dont get there fast enough as I found out a few weeks ago.

 

[james singleton]

I appreciate all of the postings concerning what it "too hot". I am feeling a little bit better concerning the temps that I am running at; but will probably still install an electric fan for assurances! Possibly install a 3-core radiator if I feel that a new radiator is needed! Thanks, keep the info coming. Jim

 

[Harte3]

High elevation with it's thin air will certainly cause it to heat. On my daily driver "Big" truck it is always a thrill to go from Phoenix to Flagstaff on a summer day with a heavy load. The fan kicks on at 205 degrees but I have to gear down to keep the engine speed up so it won't overheat. I see other trucks, motor homes, and towed campers pulled off in the break down lane all the time because their drivers don't comprehend the principle of gearing down and keeping the engine speed up.

 

[ludwig]

Where are you located? That would make a difference too if you lived Nova Scotia or New Mexico and what your majority concern would be: too hot for a couple days or 9 months.

 

[MustangSix]

In a modern car with a good powertrain controller and synthetic lubes, you could probably run the engine at 240-250 degrees (maybe more) all day long at reduced power levels. I think Cadillacs and Corvettes have a limp-home mode that does just that and they have a 195 degree normal operating temp. And even heat soak to 230-240 won't cause starting issues because of high fuel rail pressures preventing boiling in the rails and the synth oil has a much higer tolerance for heat before it "cooks off" and cokes.

But even with synthetic oils, at some point an engine gets way too hot for a carb to handle. Fuel starts boiling in the bowl and sometimes percolates causing the engine to run very badly or quit.

A more ideal temp for a carbed six is going to be between 160-180. That gives you a good compromise and buffer between operating temps and overheat. You could run 195, but except in cold climates, the additional heat soak after shutdown could cause restart issues.

Definitely do not rely on the stock gauge. It is notoriously unreliable. If in doubt, borrow or buy a good gauge or get an IR or laser type temp reader to confirm the actual temps.

 

[mugsy]

I guess the short answer is: as long as your car isn't stranded on the side of the road with steam and fluids puking out.

Personally, I think the car should run within a 10 degrees of the t/stat. I feel that the t/stat should control the temp of the water and not the water pump flow rate, surface area of the radiator, or the air speed thru the radiator.

Its true that the cap and the anti-freeze raise the boiling point of the water. And these all help. But I like to have a "cushion" or extra capacity to transfer heat from the engine cooling system, just in case I'm stuck in traffic or its an extra hot day.

tanx,
Mugsy 8)

 

[woodbutcher]

My truck(84 F150)300 6 runs so cool that the temp needle has yet to get to the "N" in "Normal".180# stat.Original radiator,clutch fan.
Leo

 

[Jamie Miles]

My car runs around 165-180 this time of year. In the summer, it runs 185-200. I do not find a car running hotter then 220, normal or acceptable. Something is not doing it's job if your car is running that hot.

That said, these engines are ridiculously tough. A couple of years ago when I still had an old plugged up radiator, I was sitting in traffic one day in July and didn't think to keep an eye on the temp gauge. By time I realized something was wrong, the SunPro temp gauge was pegged past 250! I immediately pulled off. I could hardly open the hood everything was so hot. You could not hardly bare to get near the engine compartment it was so hot. I ran that engine for two more years after that without a single problem!