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Technical Define "Overheating"

Discussion in 'The Hokey Ass Message Board' started by choppedtudor, Mar 20, 2014.

  1. choppedtudor
    Joined: Nov 28, 2009
    Posts: 687


    I continue to see threads here relating to issues of "overheating" especially with flatheads. My big question is: At what point does the temp of your motor qualify as "overheating". The way I understand it, water alone will boil at 210F...50% anti-freeze, slightly higher...but we're talking at atmospheric pressure. Now I would assume most guys are running some sort of pressure cap on their radiator...3lb. 7lb. 10lb....something, right?
    So, let's say, at 7lbs, with 50% propylene glycol...what temp with cause "overheating"...260? 270? How is it that so many people have problems with cooling their motors? You'd have to actually be popping the relief on the cap, and if thats's the case, you're not leaving an air-space in the top of the radiator for expansion. Your thoughts?
  2. Water boils @ 212. Every pound of pressure in the system raises the boiling point by 3 degrees. So a 15LB cap raises the boiling point to 257 (without the help of coolant). "True" overheating is a good question, but most would say when it starts puking. ME? I shut my old cars off at 220 (new cars run much hotter for various reasons). 220's not overheating, but, it's on it's way so I shut em off there. Most my experience in overheating (puking it's guts out) was with an idiot lite, not a gauge, so I can't tell you the actual temp when that occurred.
  3. Oh, and even tho a motor may not be "overheating", heat is what kills just about anything on a car. Look at NASCAR. They have pumps and coolers for EVERYTHING (manual trans/differential/power steering, etc)
  4. afaulk
    Joined: Jul 20, 2011
    Posts: 1,194


    One funny fact about high operating temp. is that it decreases engine wear (specifically cylinder wear). Several years ago GM discovered that cylinder bores wore less than half as fast at 185 F. compared to 160 F. Soooo, they started installing 185 thermostats, then 195. I have driven a Cat diesel powered truck lots of miles with the temp staying at 220-225 degrees. In traffic it would cool down to 185. Go figger....

  5. choppedtudor
    Joined: Nov 28, 2009
    Posts: 687


    I'm looking at a new coolant made by 'evens' that contains NO water and calls for NO water to be mixed with it...they claim that it CAN'T boil, nor will it freeze. Too good to be true? Anyone heard of this?
  6. OldBlueOval
    Joined: Jan 10, 2006
    Posts: 197

    from Upstate NY

    Just a thought get a heat gun and point it on different areas of the radiator and engine to get a good idea wear the heat is. I found out that my reworked radiator had plugged spots! I messed with over heating problems for two years. also your fan deflector, changing the angle also helped. I ran a product by royal purple called water wetter that dropped the temp.
  7. To me its when your coolant boils.
  8. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    from florida

    I'm old fashioned and anything over 180 scares me, but the new cars run hotter, much hotter. When I got my new daily driver it has a digital readout on the dash and it would read 213-221 sometimes so I called the dealer. They told me to stop looking at the dash ! :eek: My one Son's Vette runs at 221 all the time and the fan doesn't even come on till then.

    But hot rods seem to want to puke when you get to that 210 or so mark for some reason.

    Joined: Jan 18, 2011
    Posts: 1,277

    from alabama

    Beware of Water Wetter....if it blows out on polished stains aluminum to the point it's almost impossible to get it polished back without taking the part off and using a buffer.
  10. 210 is where an engine will run most effiecent (sp),
    drive it and don't worry bout it
  11. Road Runner
    Joined: Feb 7, 2007
    Posts: 1,257

    Road Runner

    Evans NPG+ is a waterless coolant that starts boiling at 375 degrees.
    It doesn't form bubbles on the cylinder walls, like water based coolants do, so it flows better around the cylinder walls.
    It lasts for the life of the engine and never needs replacing and doesn't rust the engine or radiator and you can run it with a 0 psi radiator cap.
    Not cheap, but works for many.
  12. Fossil
    Joined: Jan 9, 2006
    Posts: 357


    I've been running Evans in my hot rods for years. Go to their website and read up. It's great stuff.

    Posted using the Full Custom H.A.M.B. App!
  13. Fenders
    Joined: Sep 8, 2007
    Posts: 3,921

  14. rat nasty
    Joined: Jul 22, 2007
    Posts: 684

    rat nasty

    Evans told me that it would actually run a bit hotter but is designed like was said not to boil till like 375* and I needed to pay more close attention now to my oil temp not my cooling system never tried it but had thought about it...

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  15. choppedtudor
    Joined: Nov 28, 2009
    Posts: 687


    so it's not all just hype then...good to know. I do worry about the corrosion issue with aluminum and steel together, more than actual cooling. I have a new radiator and a fully shrouded electric fan (I know..slam away) With a 471 blower I needed to go with a custom set-up all around. The ol' flattie will be happy when I'm finished.
  16. Road Runner
    Joined: Feb 7, 2007
    Posts: 1,257

    Road Runner

    I have 3 gallons of NPG+ leftover, if anybody wants it for 1/2 price.

    Yes, the temp gauge will read a little higher than with water based coolants, but its not because the engine runs hotter.
    The same effect that keeps the cylinders cooler, gives a slightly higher reading on the temp sensor bulb.

    Cylinder/piston wear is at minimum just below 200 degrees, that's why modern engines run with 195 thermostats.
  17. Chevy Gasser
    Joined: Jan 23, 2007
    Posts: 712

    Chevy Gasser

    Yep, Nascar has coolers on everything but they won't shut anything off including the motor if it is only 250*.
  18. VoodooTwin
    Joined: Jul 13, 2011
    Posts: 3,455

    from Noo Yawk

    Overheating: when the coolant temperature is higher than the maximum recommended by the manufacturer/builder.
  19. GregCon
    Joined: Jun 18, 2012
    Posts: 689

    from Houston

    Completely wrong. They went to higher temps because it helps a good deal in meeting emissions goals.

    The iron used in engine blocks was for decades formulated to wear the 'best' at 180 degrees. That's why running no thermostat, and running at cold temps, accelerates wear. So somehow people started to think that higher temps are better for low wear. Unfortunately not so.

    Using special liquids in an attempt to not boil-over is just a Band-Aid for a lousy cooling system.
  20. squirrel
    Joined: Sep 23, 2004
    Posts: 51,244


  21. bgbdlinc
    Joined: Jan 11, 2002
    Posts: 522


    ...anybody tried Evans in a flathead? I understand that the increase in oil temp also reduces oil pressure to some degree which is a concern knowing that it already happens when the flattie gets hot (i.e. 220+)....
  22. Road Runner
    Joined: Feb 7, 2007
    Posts: 1,257

    Road Runner

    Here is a graph showing cylinder wear and temps:


    And the link explaining it:

    Many years ago, I hauled a 650 lbs. engine up into my mountains with my truck and the 235 with the Evans NPG+
    It was 3500 ft altitude increase and 40 miles distance on the freeway with 100 degree outside temp.

    The engine quickly heated beyond 180 and eventually the temp gauge pegged at 220.
    I kept driving because of the high boiling point of the Evans stuff and made it home fine with the engine never losing power or the oil pressure dropping too low.
    I would have never done that with a water based coolant.

    I am still driving the truck and the same engine 7 years later.
    That engine was rebuilt about 40 years ago.
    When I got it, it had no thermostat, the radiator was leaking and had only water and the idle speed was set very high.
  23. I had a 40 Ford sedan in the 80's with a sbc and when my wife and the twins got caught in Columbus,Ohio traffic at the nationals my car Overheated.

    My definition of overheating is water pouring out along with steam,the water & antifreeze in the radiator is rolling and it was howling like a wounded animal.

    I thought the engine was a goner for sure but after a few hours and replacing the lost coolant,everything was fine but the bottom seam on the aluminum radiator did leak.

    Griffin Radiator was less the 12 miles from my home and I had a friend that worked there and they made me the first aluminum radiator for a hot rod,their main focus was on NASCAR at that time.

    When I returned home I pulled the radiator and took it back,my friend said they would make me a new one at no cost because he thought there might be a internal problem with coolant flow so he tossed it up on a vertical band saw and gut the top tank and bottom tank off.

    The problem was confirmed over half the coolant fins were filled with epoxy,he couldn't figure out why it was such a horrible job but the replacement never gave me any problems.

    BTW,there was a 32 Chevy sitting beside my 40 that had also overheated,his problem was a nightmare,it got so hot his electric fan had started to melt,scorched the candy apple paint on the hood,the poor guy was actually crying.

    He told us he was from Florida and this was the first time he had his car on the road after a 10 year rebuild. HRP
  24. Overheating is not boiling over, it is the point that the temperature begins to do damage to the engine. I have seen the heads on a flatty glowing red (after dark and no streetlights). We used to call that poppin hot and I have to make the assumption that the engine was overheated although once it was allowed to cool down it still ran.

    Anyway it has nothing to do with the boiling point of your coolent and everything to do with the damage that the heat does to your engine. I had my small block up to 230 a few years back and still went and raced it all afternoon. I didn't like seeing that temp, for me on an older engine 210 is too hot but that is just me I suppose. The LS whatever in the wife's late model runs consistently @ 210.
  25. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547


    SAE study proved wear is lower in a higher temp motor as water and excess acid vapors are boiled off quicker , as for emmisions yes it helps , but also in the older motors you were running a wet manifold and to get power you needed more air as fuel vapor displaces the air , higher air temp displaces air molecules as they expand also so higher manifold temps less fuel charge . with a dry manifold no fuel to take up the extra air space . thats why Fi cars can get the numbers they get running hotter and more efficent . and gasoline boils at 190* so closer to that point the more its in a vapor form .

    for me overheating is when the radiator is puking , or 260 * as thats the point were mineral oil will start to coke .

    on my last Cat I owned ( c-15 550Hp ) it ran at 200* the motor at 500,000 miles had minimal wear . my old 425 Hp 3406 at this point with a 160 stat it was overhaul time .
    Last edited: Mar 21, 2014
  26. BootleggerMatt
    Joined: Aug 17, 2011
    Posts: 258


    My 460 runs at about 200F during the summer, stays at the thermostat temp during winter, It gets up to 220F in summer traffic... has a 13lb cap, never boils over. It threw a fan belt once and it got up to 250F while I was trying to get to the gas station off the highway. It puked and steamed and boiled over, but I put on my spare belt, filled it with water and no problems since. My personal preference is anything over 230F and I start thinking about pulling over, I don't want my oil being over 240F for long and from what I've heard 240-250 is the danger zone for fossil oils and they begin to break down.
  27. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,856


    To me, overheating is when your coolant vaporizes into steam, causing a massive increase in pressure, which causes the safety mechanism (pressure cap) to blow off pressure. The voids created by the loss in coolant allow areas inside the engine to superheat. The superheating causes warpage and causes the engine oil to breakdown or even burn.
  28. blowby
    Joined: Dec 27, 2012
    Posts: 8,403

    from Nicasio Ca

    Air cooled engines run much hotter, up to 400 degree F cylinder head temps.
  29. All of the above. I could be okay with the temp creeping up towards 200 in traffic on a hot day, running between 180-190 I'm okay with.

    I'm glad that my OT 2012 ride is just a gauge with no numbers. I would have to put duct tape over it if it did.

    With my stock cars, I really had no problems with them getting hot even in a 50 lap feature race with plain water. They ran 190-200 even pulling 6500 RPMs all the way. But shut it off in the pits and it could be puke city. On hot nights we would pour water over the top tank and let it run until the numbers came down a bit.

  30. tommy
    Joined: Mar 3, 2001
    Posts: 14,757

    Member Emeritus

    That is why the modern temp gauges don't have numbers just cold, normal and hot. The new engines run much hotter than what we remember to help with the emissions standards that the factories must meet. My old Deuce sport coupe would run all day long at 190. When it would run hotter it was time to top off the radiator. Stock Deuce radiator, non pressurized. Fill it up, bring it up to temp, put the cap back on and don't look at until the temp gauge said it was low again...maybe once a season? I value our environment but my few hotrods will not cause global warming! The higher running temps on the daily drivers are a different story. The factories don't want "Joe sixpack" to know the actual operating temps.

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