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Thread: SBC 350 Overheating?? Advice Greatly Appreciated!!!

  1. #1

    SBC 350 Overheating?? Advice Greatly Appreciated!!!

    Just got my car finished this week. It's an 85 Fiero GT with a Ferrari bodykit and a brand new Chevy SBC 350. Lots of new parts in the car. I apologize in advance for a long post!

    I drove the car about 100 miles before this weekend. The stock temp gauge does not work, but the stock temp warning light does come on occasionally (usually if idling or driving slowly). Typically, moving along at a decent speed will get the temp light to turn off. I wasn't sure if the stock temp light even mattered since the stock engine was a V6 and I am running a 350.

    To monitor the temp better, I installed an Autometer water temp gauge today. See picture. The intake (an Edelbrock Performer Air Gap) seems to have 2 temp sender spots (on either side of the water outlet -- circled in red and blue). I figured that one was the temp warning light and the other was the fan temp sender, but maybe I was wrong...



    I first installed the Autometer sender at the spot circled in blue. I then drove the car and the gauge quickly pegged itself at 250 degrees. I stopped and noticed that the temp warning light was on and the fan was not running, so I guessed that I had unplugged the fan temp sender. So then I switched the Autometer gauge to the spot circled in red in the picture (as shown in the pic). I drove the car again, and again it quickly pegged itself at 250 degrees, however BOTH the fan AND the temp warning light are now working (???). Obviously I am confused. Now I'm not really sure what the two things plugged into the intake's temp sender spots are.

    I then checked my water/coolant tank and it was low, so I filled it. I drove the car again and it got hot fairly quickly (according to Autometer)... Stopped, let it cool... drove it again. This time (cruising at 40 - 50 mph) the temp stayed right about 210-220 and the stock temp warning light stayed off. I drove about 5-8 miles with no problems.

    I got home, let it idle, and the temp rose again to scary levels (230 - 250)... Shut it down and checked the coolant tank... it was way down again... used the last of my coolant to fill it back up and then logged on to this forum to get your help!

    The car does not seem to leak coolant (ie non on driveway), so I'm not sure why it was low twice...

    A couple questions:

    1. Does it matter where I install the Autometer temp gauge? (either of the two spots on the intake... or is there another place?)
    2. Both of the temp sender locations had "things" plugged into them before I got the Autometer guage. Any ideas what they are? (The electric plug that is currently unplugged is just to the left of the red circle in the picture)... any idea what that is? Is it important?
    3. How hot is too hot for a SBC 350?
    4. What do I do next???

    I am nervous to drive the car until I get a better grasp on this potential overheating issue.

    I am pretty much a noob at all this stuff, so your help is so greatly appreciated!! I'm begging for your help!! Thanks!!!!
    1985 Ferrari 328GTB Replica with SBC 350

  2. #2
    Moderator FunnyWheels's Avatar
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    Re: SBC 350 Overheating?? Advice Greatly Appreciated!!!

    It sounds like a pocket of air is in your engine. They need to be jacked up in the rear (or park on a steep hill) then start the engine adding coolant in the rear until full. You should have an air bleeder near your sensor that looks like a little screw, back it out slightly and it will disperse the trapped air. One of the sensors on that intake is used for a fan relay switch; the other is the sender for the temp gauge. If you car is running hot after you bleed the air, then try using a 180 degrees sensor or lower to turn on the fan sooner to cool the engine. It is so darn hot here in Florida I have a manual switch to turn mine on in traffic.

    Keep us posted,

    Dave
    If you're not confused, you're not paying attention.

  3. #3

    Re: SBC 350 Overheating?? Advice Greatly Appreciated!!!

    Hi Dave -- Thanks! Gonna try this tomorrow!

    You said to add coolant in the rear of the car... where does it go? My radiator/coolant reservoir are in the front of the car... not sure where to add the coolant in the back... or do I just add it to the front?

    Also, is backing the rear wheels up onto wheel ramps enough lift?
    1985 Ferrari 328GTB Replica with SBC 350

  4. #4

    Re: SBC 350 Overheating?? Advice Greatly Appreciated!!!

    I wonder if I should pull the radiator out? I confirmed with the original owner that it is the stock rad (85 Fiero GT). The car sat for about 11 years... rad might be total crap... not really sure.

    If I was to get a new rad, should I go with an OEM Fiero rad or something bigger? V8 Archie makes a 4-core direct bolt-in rad with his V8 conversion kit... ($350)
    1985 Ferrari 328GTB Replica with SBC 350

  5. #5

    Re: SBC 350 Overheating?? Advice Greatly Appreciated!!!

    Should I also flush out the system with water? Per other forums:

    1. Remove lower rad hose and flush clean water through opened rad cap to clean out radiator.
    2. Flush clean water through heater hose (with heater valve open) to flush out heater core / engine block. Refill with coolant.
    3. Remove rad cap and run engine (heater on) to force air out. Add coolant as necessary.
    4. Shut off engine, replace rad cap, and refill overflow tank to cold-full (once engine cools).

    Is this an ok way to flush and get air out, or is the "park on a hill" method better?
    1985 Ferrari 328GTB Replica with SBC 350

  6. #6

    Re: SBC 350 Overheating?? Advice Greatly Appreciated!!!

    Flushing and filling are two different beasties. I think I just fired this off to you in an email, but I'll post it here again for everyone else.

    As some of you know, I'm having issues with my 350 overheating. Things I've done to date include, but are not limited to (and in no particular order):

    1. New thermostat (try that first)
    2. Complete cooling system flush. All hoses and conduits visually inspected for crimps, dings, and damage.
    3. cooling system burp (this may take up to two hours to do properly)
    4. New 40gpm electric water pump. If you are currently running an electric pump, check the flow. A lot (like my first one) only flowed 19gpm...not enough!
    5. New 5 core aluminum radiator
    6. Radiator fan shroud
    7. Check timing and fuel mixtures

    I agree that it sounds like you've got air in the system. If you are running the stock rad, I'd swap that out too. You may get by with that rad, but the better performing ones (brass cools better than aluminum BTW) would be a good investment.

    If you were to post a picture of your engine bay, it would help. Usually on the 350 conversions, there is a manifold on the top of the block where your cooling lines run out of and head across the engine bay and then down under the car to the radiator. In that spot, I have a rad cap, which is the highest point of my system where I burp it and add coolant. In addition to jacking the car front and back, I also jack it left and right to make sure that air is not trapped in my water pump (common problem) or the top coolant line running across the engine bay.

    Check out Pennock's forums and search for "overheating after 20 minutes". That thread has tons of great info on the 350SBC conversion overheating issues.

    http://www.fiero.nl/cgi-bin/fiero/Ul...i?action=intro

    Meddle not with the affairs of the Dragon, for you are crunchy... and taste good with ketchup.<br />http://www.rc-sub.com/resources/grap...ni/avatar2.jpg

  7. #7

    Re: SBC 350 Overheating?? Advice Greatly Appreciated!!!

    Here's a link:

    http://www.fiero.nl/forum/Forum2/HTML/078605.html

    Let us know what you find out!

  8. #8

    Re: SBC 350 Overheating?? Advice Greatly Appreciated!!!

    Currently the car does not have a t-stat in it (to keep the temp down). I've seen some debate regarding whether or not to even use a t-stat -- what is your take on that? (I stopped by Advance Auto at lunch and picked up a 160 degree t-stat just in case!!) I've heard that no t-stat can mean cooler temps at low speeds, but higher temps at high speeds. My car, however, is currently getting hot at low speeds with NO t-stat....

    I also bought some rad flush stuff - probably won't do anything, but I'll run that through when I do the air bleed tonight. I don't think that there is a rad cap in the back... I might have to get one. Would I use a vented or non-vented cap for the back? Is the air bleeder screw that Dave mentioned an alternative to a rear cap?

    I just called the guy who did most of my engine work and he suggested getting a better rad with a more powerful fan and full shroud. Any recommendations?? Obviously, I'm looking for max cooling that will still fit in the Fiero... Archie makes a 4-core aluminum rad but I'm not sure if that's the best.

    Additionally, they used a water pump (that the original owner put on) that mounts to the bottom of the rad -- I have no idea what brand it is or the flow rate. I bought a Proform 35gpm pump but they didn't install it because it would have required cutting a bunch of metal to get it to fit. I guess they figured we try our luck without it first...

    Wow, I'm asking lots of questions! Many thanks for your advice! I will post some pics tonight!
    1985 Ferrari 328GTB Replica with SBC 350

  9. #9

    Re: SBC 350 Overheating?? Advice Greatly Appreciated!!!

    I'm no expert, but you should have a thermostat. Metal expands with heat, and the parts in your engine are cut and cast to specific tolerances with that in mind. Your engine is designed to run at a certain temperature. The thermostat ensures that the engine reaches that temperature quickly by blocking off the flow of coolant, meaning, the coolant can't flow in order to cool the engine until it's up to temperature.

    The whole problem here is that the radiator sits lower than the engine in the car. The air will go to the highest point, which is the engine! Thus, an air bubble can get stuck there and have trouble working its way out.
    Seeing that you have no thermostat installed currently (which would trap the bubble in the engine), I would park on a steep hill with the radiator higher than the engine (ramps are ok), and run it for a while. Since the Tstat isn't there to stop water flow, the air should naturally rise to the highest point (now the radiator). Run it for a few minutes at a time, filling the radiator each time. You should be able to work out all of the air bubbles eventually.

    For diagnosing the overheating, I would leave the thermostat out, but definitely put it back in when all is sorted out. The bigger radiator won't hurt, but I would assure that this is the problem before spending money on an upgrade.


  10. #10
    Moderator FunnyWheels's Avatar
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    Re: SBC 350 Overheating?? Advice Greatly Appreciated!!!

    Quote Originally Posted by ksteak
    Hi Dave -- Thanks! Gonna try this tomorrow!

    You said to add coolant in the rear of the car... where does it go? My radiator/coolant reservoir are in the front of the car... not sure where to add the coolant in the back... or do I just add it to the front?

    Also, is backing the rear wheels up onto wheel ramps enough lift?
    The ramps should be enough. Fill the radiator up before you begin the process to get the air out of that end then lift the car up in the rear. This is standard operating procedure on a stock Fiero as well. You might be able to unhook a heater hose and fill it from there. Use a funnel. If there is no air in the system, it will consume very little coolant. If there is air then you will more than likely put in a gallon or so.

    I used a part in the radiator hose that helps with these situations.

    See Attached.

    Dave
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    If you're not confused, you're not paying attention.

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