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Old 08-20-2004, 08:04 PM
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Why is my sbc chevy 350 getting so hot?

My 350 runs at about 190 degrees which is great.When I sit in traffic for a couple of minutes it shoots up to 230 degrees.The other day I did a nice long freeway run(about an hour.pushing her alittle hard...I hit a 100mph a couple of times) and got stuck in traffic.My temp got up to 250.I pulled over shut her down and the radiator boiled over.I lost about 2 cups of fluid on the ground.Can someone tell me what is going on here??Do I need a new thermostat?Or could it be something else?How hard is it to change out a thermostat?Sorry...still waiting for my 350 sbc books.thanks bm

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Old 08-20-2004, 08:11 PM
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It sounds like you simply don't have enough airflow through the radiator at slow speeds. What kind of fan are you using? Also, make sure you have a fan shroud on. This is very important.
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Old 08-20-2004, 09:00 PM
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Check your timing, if you are running too advanced, it can cause the engine to heat up, provided it is not detonating. Also check your fuel mixture if you are carbureted, too lean will also heat things up. If you have a clutch fan, check to see if there is significant resistance when you spin the fan by hand when the engine is turned off. If the fan is very easy to move, you may have a worn out clutch assembly. I had this problem not too long ago, I swapped out for a flex fan and it made a world of difference. If this does not help, check if your rad is adequate for the engine you have. If you have 300 horsepower, a single core rad just won't cut it.

Oh and by the way, you probably don't need a thermostat, if you don't overheat on the highway, your coolant is circulating well, which means the thermostat is open. If you must change it, simply remove the top radiator hose, remove the thermostat housing and gasket, pull the old one out, and drop the new one in the same way. Install a new gasket and seal it with automotive silicone, put the housing back on, connect the hose and you're done.

Last edited by Mad Maggot; 08-20-2004 at 09:00 PM.
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Old 08-20-2004, 09:40 PM
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I have a 350 in my 72 Chevy truck and it runs about 160 driving seldom gets up to 190-200. I have a flex fan and a 3-core radiator. All in all, she runs pretty cool most of the time, unless pulling heavy loads are sitting in traffic, but it still doesn't go over 200. Your's sounds like the fan isn't doing it's job to me. What all have you got on it? Accessories??
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Old 08-20-2004, 09:57 PM
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I have ac and no fan shroud
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Old 08-21-2004, 01:12 AM
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Shroud

[color=yellow][size=2]Doc

90% of your problem is going to be no shroud....Run, don't walk to the nearest boneyard and pick one up before you fold, spindle, mutilate or dement parts!

I would Flush and back flush The system next, to get all the old crap outta the system.

Replace the thermostat with a Failsafe type just because... they are cheap and eliminate the possibility that the old is bad.

Check the hoses, be sure the lower hose isn't collapsing under hard running, if they seem weak, replace them anyway. Be sure no part of the upper hose is lower than the gooseneck on the manifold, this will cause an air bubble that will lodge in the water pump causing heat.

Check or replace the Radiator Cap, (you can get the guys at like autozone to test them for free...)

Be sure you refill with a 50/50 or better mix of anti freeze.

If equipped, Check the Fan Clutch.

Don't know the year, or Car, but other obscure things to look at:

If you have a heat riser in the Exhaust manifold collector, check to see that it isn't sticking

If you have an EFE be sure it's working (this shuts off the flow of exhaust on the right side until the engine warms up) I think (therefore I have headaches) No vacuum to the EFE is closed, Constant Vacuum to the EFE is open.

If you have a Cat, be sure it Isn't plugged. or Exhaust pipes aren't bent.

Engine Wise...
as said before....
If your timing is over advanced this will cause heat.

If your Carb is way too lean it will heat up too.

Check the oil, just to be sure no coolant is in there.

Hope it helps!

Doc
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Old 08-21-2004, 08:01 AM
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I am just going to chime in on the timing thing. Too slow timing typically makes the engine run hot. Too fast might make some difference as well, but typically slow is worse. You want the total timing with vacuum advance to be in the 20 range at idle and around 45 or so cruising with no load.

I was having trouble with my S-10 running hot while I was working on tuning the ECU and found slow timing was part of the culpret. I was only running about 36 total at cruise. I bumped it to 42 and EGT and water temp both dropped. I also bumped initial timing up to 22 from 20 which helped idle temperature.

Chris
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Old 08-21-2004, 08:36 AM
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like doc says,
a fan shroud is a must for any engine. it will drop your temps about 10 degrees.You may want to consider an electric fan to improve your temps in traffic. You basically have a good engine with an insufficient cooling system.
ps do not heat your engine to 250 too many more times or you may wind up with worse problems.
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Old 08-21-2004, 07:36 PM
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Do I need to drain my radiator to put in a new thermostat?Thanks bm
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Old 08-21-2004, 09:16 PM
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First things first, if your radiator fluid is nice and green and your current thermostat is working, leave it alone and take care of the actual obvious problem you have which is no fan shroud. The best tuned and cared for motor will run hot without a fan shroud.
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Old 08-21-2004, 09:45 PM
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yes you do have to drain the radiator.you should pull your stat out right away since it is about the eseaist and cheapest thing you can do and see what temp. it is unless you already know.i don't remember you saying.try putting a colder stat in and see what happens.the next best thing you can do is go with an electric fan.you won't regret it.you can also for the time being till you cure the problem try going with a higher press. rad.cap.the higher the press.if it running hot,the longer it will take to over heat.if all that fails you may want to go with a perf.alum. water pump.good luck
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Old 08-21-2004, 11:14 PM
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get a fan shroud for sure. the fan is only abot 25 - 30% effective without one. don't run with no thermostat unless it happens to stick closed on you. not good for engine cooling as the coolant can't absorb enough heat from the engine or dissipate it through the rad while flowing at aroung 75gpm. totally agree with s10, advance your timing 5 or 6* and see what happens. if the temp hit 250*, change your stat, it's only a couple of bucks, and is good pm.



doc, isn't no vacuum open and vacuum closed? i might be screwed up, though.
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Old 08-22-2004, 12:17 AM
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EFE

[color=yellow][size=3]Doc Here

Sbchevfreak,

I can't remember for sure, but the line comes from a ported thermo Vac switch on the intake manifold that opens when warm, but I'm not for sure if that switch closes or opens vacuum on warm.

That's kinda why I said I wasn't sure about that, The memory is getting old...Meeting new friends and family brand new , each and every day.now..Oldtimers...Selective Endorphin misfires...It's just plain tough gettin' old...


Doc
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Old 08-22-2004, 01:51 PM
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I went through a similar problem with my 350 SBC last year. Although I never got as hot as 250*, I was consistantly running at around 220*. First thing I did was to hook up an overflow tank to my radiator and "burp" the system. The overflow tank keeps your radiator from sucking in air, which doesn't help much in cooling your engine,every time it gets hot and spits out some fluid in a boil over. Getting rid of the air in my system and preventing it from sucking more in dropped temps about 10*. Next, I got a shroud on it. That got me down to about the 200*-205* range. After that I re-did my timing, adjusted my A/F mixture and replced my T-stat with a new, lower temp one that I drilled a couple of 1/16 holes into to allow a little flow even when closed. Now my engine runs at a pretty consistant 190*-195* with no problems. George, aka 1Bad80, was a huge help to me when I was having my problems with temperature. These are the suggestions that he gave me and they worked- maybe they can help you too. Good luck!
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Old 08-22-2004, 02:02 PM
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green monster,
I have an overflow tube which hangs straight down to the bottom of my engine bay.this is where it dumps when it overflows.are you saying this tube should be hooked up to an overflow tank?How do I burp the system?I ordered a universal shroud that will be here in a couple of days.What temp termostat do you recommend?I think I have a 195 in there now.Also are you sayiny to drill small holes in the thermostat itself?Thanks for the help. bm
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