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SBC engine temperature...what is too hot?

Discussion in 'The Hokey Ass Message Board' started by Bluesfella, Jun 6, 2008.

  1. Bluesfella
    Joined: Apr 30, 2004
    Posts: 146


    What is the best operating temperature for a small block?

    My daily driver '55 Chevy has a stock-type radiator in it. I drive it regularly in the heat here in N. Florida, and I use the A/C sometimes when it's really hot.

    I've noticed on the hottest days when I'm sitting in traffic, the temperature can climb to almost (but not quite) 220...that makes me a bit nervous.

    So, at what temperature should I be concerned?
  2. RodStRace
    Joined: Dec 7, 2007
    Posts: 2,708


    stock radiator and A/C????
    If the system is pressurized, it should be able to handle over 212 (boiling), but that may not be the best for longevity.
    Late model stuff runs at that all the time, but it's for emissions and they are designed for that temp. Another question is where the sending unit is. Between the plugs or by the thermostat?
    If that's the top end temp you see, make sure the whole system can handle it and you may be okay. However, if it goes higher or any part is weak, you are living on borrowed time.
  3. nailheadroadster
    Joined: Jun 7, 2006
    Posts: 1,522


    North Florida here also so I understand the heat you are talkin about. I like to see around 185 during the summer. Looks like it's time for a new radiator for you mang.

    Tough to beat this deal =

    Keep the mechanical fan & stock shroud. Add a 16" electric pusher to the front of the radiator. Install a new 16 lb cap. Refill with Extended Life Coolant (Pennzoil or Shell Rotella) and add 2 bottles of Redline Water Wetter.

    Yeah, you'll have to spend about $450, but you will be a happy camper and so will the engine.
  4. tjm73
    Joined: Feb 17, 2006
    Posts: 3,403


    Unless you have a really hopped up SBC you should be able to keep reasonably cool (~200-210 sitting still in traffic) on those blistering days in traffic.

    How do you move air through the radiator?
    Is the radiator big enough?
    Does it cool down under motion? How much/too what temp?

  5. Bluesfella
    Joined: Apr 30, 2004
    Posts: 146


    Yes, but I do have an additional electric fan that comes on with the A/C. It generally stays under 210, but on really hot days when I'm sitting in traffic I start to get a little worried.

    I have thought about upgrading the radiator, but that's why I want to know what kind of temps I should be concerned about.

    More info on my setup:
    290hp GM 350 crate motor
    Automatic trans (trans cooler is built in to the radiator)
    mechanical fan, but I turn on the electric fan when it's hot
    full fan shroud
  6. If it goes to 220ish and doesn't get any hotter, and then cools down once you start moving you're probably OK.
    Rule of thumb is if it runs cool during normal driving, radiator size is generally good. If it gets hot when sitting idling then you have an air flow problem. you are not putting enough fresh air over the radiator when stopped. Bigger or more efficient fan, better shroud etc.
  7. You say it generally stays under 210 - if that is during normal driving, i would look for a bigger or more importantly, more efficient radiator.
    I like to see 180-190 during normal driving, A/C on on a hot day. 200-210 when sitting at a light and then cools back down as soon as you are moving again.
  8. Bluesfella
    Joined: Apr 30, 2004
    Posts: 146


    My car is a '55 and the radiator is in the 6 cyl position. Which is fine, but there's no room for a pusher fan. (In a '56 or '57, there is plenty of room!) My electric fan (I think it's 16") is set up as a puller...supposedly more efficient that way anyway.

    I'm thinking about upgrading to an aluminum radiator, but instead of the ebay one, I think I'll go with a more modern crossflow design...something like this, maybe?
  9. Bluesfella
    Joined: Apr 30, 2004
    Posts: 146


    I'll pay close attention when I leave work's hot today, plenty of traffic...and I'll run the A/C and check the temps. I know it doesn't get down below 200 with the A/C on, even at 55 mph...but I'll double-check it.
  10. Cross flows are definitely more efficient. There's still tons of argument about Cooper/Brass vs Aluminum. Factories went to Aluminum to save weight to help meet CAFE fuel mileage requirements not because they were better. It has more to do with tube size, fin count, etc. Copper/Brass dissipates heat better then aluminum but construction techniques with tube size allow Aluminum to work equally well under most circumstances, as long as you are comparing equal quality.
    Do you have a shroud with that puller fan? And is it mounted at he right place for the electric fan? An improperly placed fan in relation to the shroud can actually inhibit airflow! And yes pullers are better than pushers.
    If it's over 200 at 55 I'd be looking for a new radiator!
  11. Hot Rod To Hell
    Joined: Aug 19, 2003
    Posts: 3,032

    Hot Rod To Hell
    from Flint MI

    When it starts puking coolant, it's too hot. Seriously. Otherwise, anything under 250 isn't gonna hurt it.
  12. scottybaccus
    Joined: Mar 13, 2006
    Posts: 4,109


    agreed. 220 is normal for an efi car with the right cap pressure rating. 240 is where concern begins. You'll get much better combustion at 200 or better. One of the emmisions issues with older cars was the unburned fuel going out the tail pipe with the 160-185 temp. Oil temp is also key. If you really want to know what's up, get an oil temp gauge. 185 is minimum there.
  13. jusjunk
    Joined: Dec 3, 2004
    Posts: 3,138

    from Michigan

    thats crate motor should run 180 all day long. id suggest also a new radiator. Ive got a 305 in my 32 roadster with a moon style tank in front of the grille and i stuck a for sale sign in the grille and i have a 16 inch electric puller fan and its been dam near 90 here and the damn thing runs 180. It does have a aluminum radiator too.. Old engines with clogged up water passages and old radiators can be a problem.. Id bet if you put a new one in you will be pleasantly surprised..
  14. AnimalAin
    Joined: Jul 20, 2002
    Posts: 3,417


    Before you spend a big chunk of your hard-earned cash on a replacement radiator, confirm the temperature reading. 220 on the gauge may or may not correspond to 220 at the engine.

    It seems from this thread we have more than one school of thought on the subject. Not that I am an expert, but my thinking is that a modern engine with modern lubricants should be able to handle the temperatures that modern cars run. If it doesn't puke, ping, or vapor lock, drive it and keep changing the oil and coolant regularly. No reason to think running it just like a new car will hurt it.
  15. Bluesfella
    Joined: Apr 30, 2004
    Posts: 146


    It's never lost coolant, at least not in a long time. It's got a new(ish) cap on the radiator, and when I put this car together, I had the radiator pressure-checked. The radiator guy told me he thought it was an "upgraded" radiator, but it looks stock.

    I have a Danchuk shroud (meant for a mechanical fan) that covers the whole radiator. It lines up perfectly with the mechanical fan, with the fan sticking out about an inch past the shroud.

    The electric puller fan is inside that shroud, mounted directly to the face of the radiator, with some padding to prevent metal-on-metal contact. It lines up approximately where the A/C condenser is on the front of the radiator.

    It's a new Autometer electric temp gauge, with the sensor in the driver's side head. Where and how should I confirm that it's correct?
  16. AnimalAin
    Joined: Jul 20, 2002
    Posts: 3,417


    How about one of those point and shoot IR thermometers. Point it at the head, thermostat housing, radiator top tank, etc., sort of average the measurements. Probably give you an estimate of how hot it really is.
  17. Bluesfella
    Joined: Apr 30, 2004
    Posts: 146


    Here's fancy diagram of how the electric puller fan is mounted. Everything is kind of crammed in there, but it does seem to cool it better with the electric fan on.

    Attached Files:

    • fan.jpg
      File size:
      24.7 KB
  18. You have both mechanical and electric, inside the same shroud? Maybe you only need one or the other, could it be causing turbulance in there? I have a 318, auto trans, closed hood, mech fan, A/C, P/S, P/B, and it never runs hot in Houston stop and go traffic.
  19. You put this up while I was typing, so I guess my suggestion is moot.
  20. DrJ
    Joined: Mar 3, 2001
    Posts: 9,418


    You need manifold sourced vacuum to the distributor vacuum advance before making any other changes.
  21. something else to consider is timing. make sure you're not running it to advance that will cause over heating too. somthing else to check as stated before get a lazer pointed temp gun, check surface temp of head and intake at thermostate. it could be reading temp from the exhaust if it is close to that. we always put them in the intake right next to the thermostate. that gives you the true temp of the water as it leaves the motor. somtimes at the head if the sending unit is close to the exhaust the the metal on the temp sending unit will heat up and show it reading hotter then the water temp is inside
  22. Kikinrods - I've often wondered about the accuracy of using an IR gun where you are measuring the skin temperature versus the dynamic circulating coolant temperature as measured with a temperature probe. Seems to me that skin temperature change would be a delayed measurement versus a dynamic measurement. What's your experience been?
  23. There is a lot of misinformation about ignition timing and cooling. Retarded timing contributes to overheating. When the timing is retarded the spark occurs closer to top dead center. When this happens there is much more compression at the time of spark which generates more heat, causing the motor to run hotter, not to mention a loss of power. The loss of power means the motor has to work harder further causing a hotter running condition. Advanced timing helps cooling. Bump up your initial timing a few degrees and see if it helps the car run cooler. It's an check. Of course, if you advance enough to enter pre-ignition or detonation (pinging) you will start to overheat also. Detonation contributes to overheating. If you start to detonate back off the timing a little. Overheating cars should always run vacuum advance. Vacuum advance also helps cooling as long as there isn't detonation.

    It is also true that we can run motors hotter today then in the past. Radiators and colling systems are better designed to handle the increased pressure that heat induces. Part of the reason that lower temps were desirable in the old days was due to oil technology. Old oils broke down at much lower temps than todays oils which can sustain 250 degrees of oil temp before breaking down and causing a loss of protection.
  24. sdluck
    Joined: Sep 19, 2006
    Posts: 2,795


  25. Bluesfella
    Joined: Apr 30, 2004
    Posts: 146


    So, I drove it home yesterday, then to a cruise-in tonight. I was wrong when I said it gets up to 220, it's actually 210 that's the max.

    Yesterday, in stop and go traffic, it varied between 195 and 205. Today, on mainly 55 mph open roads, it was around 200 (but it's really hot today).

    Both days I had the A/C and the electric fan on full time.

    I am also using vacuum advance, and the timing is set per specs of the crate motor (provided by GM).

    I think I'll look at upgrading the radiator eventually.
  26. noboD
    Joined: Jan 29, 2004
    Posts: 7,776


    Sounds like you may not have a problem worth worrying about.
  27. Mr48chev
    Joined: Dec 28, 2007
    Posts: 30,054


    I second that. I also agree with the concept that if it isn't puking water it isn't hot.

    The vehicles that engine was intended for run thermostats that open at 195 to 205.

    If you can run 210 in traffic with the ac on you are still two degrees below the boiling point of water. Add the raised boiling point with the antifreeze ( coolant in so TX) and the raised boiling point with the pressure cap and you don't have a problem.
    Yea if you had a 52 Chevy with a 216 in it that would be hot but that isn't hot for that 350.

    I have seen electric temp gages that are not all that accurate too. My preference has always been a mechanical gage.
  28. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,912

    dirty old man

    I know you said it runs cooler when you turn on that electric fan, and I don't doubt that. But what I do doubt is what contribution the electric fan is making vs it not being there at all! I believe it could be acting as a baffle till you turn it on, and then perhaps it acts less a baffle and doesn't inhibit airflow quite as much.
    Have you run the car at all with just the mech fan and that electric fan not only switched off, but off the car?
    You can lessen the heat load on the radiator and contribute to transmission longevity by installing a seperate trans fluid cooler. Use the plate type, they're more efficient in BTU removal vs physical size than the tube and fin type.
    You can even go so far as an engine oil cooler to lessen BTU exchange load on the radiator.
    If your radiator has been boiled and rodded and flow tested, I'd look further before I spent big bucks on a special radiator.
  29. stuart in mn
    Joined: Nov 22, 2007
    Posts: 2,000

    stuart in mn

    I would think the electric fan shouldn't make much difference on the temperature when you're driving 55mph - maybe it is blocking airflow.
  30. Judging by what you say here, and the fact that it's a late crate motor, I wouldn't worry about it

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