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Old 01-10-2009, 08:24 PM
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350 sb overheating

Ok I have viewed all the post on over heating engines and have done pretty much everything that was recomended. Ok about my engine, is a 350, with a brand new water pump, thermastat,raidator,hoses, new cap, no leaks, oils clean not milky, engine has lots of power, timings correct, fuel mixtures good. It has headers, victor jr intake, average cam, average carb. Ok what it does is no mater if fan is on or if thermastat is in it will rise in temp until it is cut off. Driving or sitting still has no effect. Everybody i know is stumped and the only thing ive yet to do is check to see if the head gaskets are on wrong. So any ideas whats going on.

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Old 01-10-2009, 08:30 PM
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What did you do so we aren't repetitive. Feel the hoses and all that crap? Do you get heat?

What kind of intake? What kind of t-stat. The reason I ask is that on some intakes the T-stat can bottom out and not have enough room to open, causing a heating problem

I have a BRAND NEW ENGINE and I had an over heating problem.. The T-stat got stuck. A brand new t-stat. Did you replace the T-stat, cheap, easy.

There's not much to a cooling system. It either leaks or it doesn't and all you have is a T-stat and a pump.
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Old 01-10-2009, 09:11 PM
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are you sure they got you the right pump at the parts store and not a reverse rotation pump. just a thought.
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Old 01-11-2009, 07:53 AM
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Yeah

All those are great help, infact thats the excact first things me and all my friends came up with, but sadly nothing helped. I changed the hose because it was getting sucked shut, so the the hoses are new and work fine. Both hoses get hot. The entire radiator gets hot so its flowing good, and the third one ive put in it. Also put the right flow water pump on and nothing helps. the thermastat thats was on it worked fine, I checked it in boiling water, but I took it out to makle sure and it still over heats. Now the only thing that kept it at 215 the longest was keeping the radiator cap open relaeasing pressure. The fan both flex and electric made no impact good or bad. My other buddy said maybe the head gaskets are on wrong, blocking a water hole or two, but im trying to do all I can beforer pulling the heads. But im runnig out of ideas and things to try.
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Old 01-11-2009, 08:01 AM
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Quote:
Originally Posted by beast10
All those are great help, infact thats the excact first things me and all my friends came up with, but sadly nothing helped. I changed the hose because it was getting sucked shut, so the the hoses are new and work fine. Both hoses get hot. The entire radiator gets hot so its flowing good, and the third one ive put in it. Also put the right flow water pump on and nothing helps. the thermastat thats was on it worked fine, I checked it in boiling water, but I took it out to makle sure and it still over heats. Now the only thing that kept it at 215 the longest was keeping the radiator cap open relaeasing pressure. The fan both flex and electric made no impact good or bad. My other buddy said maybe the head gaskets are on wrong, blocking a water hole or two, but im trying to do all I can beforer pulling the heads. But im runnig out of ideas and things to try.
When you put the head gaskets on, you did slip them onto the guide pins right? otherwise how did they sit flat?

Boiling water isn't a definitive test as the stat isn't under pressure. It's more of a guideline. Since you ran without it I guess we can eliminate that. Are you 100% positive on pump rotation? Is the pressure cap good?

Last edited by Jsup; 01-11-2009 at 08:26 AM.
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Old 01-11-2009, 08:30 AM
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What head gaskets did you put on, i went and looked at a set felpro that i am fixing to use and they are same from what i can tell there is no right or left side on them. If you didnt get them on the guide pins you wouldnt be able to bolt the heads up on the engine as the gasket would block the head bolt holes in the block i would think. I have chenged head gaskets on a few sbc engines and never worried about how the gaskets went on and just made sure they were on the guide pins right and torqed them down.Could be a head gasket with a defect like all the holes didnt get punched when made.
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Old 01-11-2009, 09:43 AM
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other ideas:

1) new rad, but blocked tubes maybe? cheap made in PRC?
2) have a fan shroud?
3) proper CFM for elec fan? Flex fan proper distance from rad?
4) you didn't say where the heads came from--if they weren't new, did you check the water passages for blockage, etc--hot tank does not remove water passage buildup very well.
5) sometimes there is even casting mess inside the water passages--I recently had to break up and pull out with long skinny pliers a piece of cast iron about 6" long that had been rattling around in there since the engine was new (70's smogger heads)
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Old 01-11-2009, 09:47 AM
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what car???
what radiator demensions??
is the radiator top higher than the highest point on the motor that does have coolant so it can purge the air???

start it cold with the cap off....
once the stat opens there should be a "rapid river" of coolant flowing across the the top you can see...
(let it idle 15 minutes open,,,to help purge any trapped air)
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Old 01-11-2009, 09:56 AM
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Have you confirmed that your temperature gauge is working ? Will the engine actually boil over ? I have let them run with the radiator cap off and stuck a meat thermometer in the radiator.
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Old 01-11-2009, 01:55 PM
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My advice would be to first, go buy a cheap mechanical gauge for about 12 bucks at any autoparts store to be assured yours is working correctly.
Next, is the resivoir still in use? does the overflow line coming out from under the radiator cap connected to the resivoir or is it shut?
GM cooling systems must be vented to work correctly, so if the resivoir is not in use it will over heat. Now my cutlass with a 350 sbc was running hot, and I couldn`t get it to stop. So, I found the owners manual and filled it to how GM recommended. The way I always did it was start the engine and fill it, that way its full after the T stat opens. However, this causes problems because then the system isn`t vented, it`s packed with coolant so it can`t vent. So what you do is drain a good bit of coolant out, about half way down the radiator amount, then replace the cap, start the engine, and fill the resivoir to the "full hot" level. Watch the resivoir, you`ll see the air purging out as it pulls coolant in. Next you keep adding coolant to the "full hot" mark until the level no longer goes down. After I did my cutlass this way it didn`t run hot anymore. Ever since then I fill all GM vehicles I work on this same way.
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Old 01-11-2009, 02:54 PM
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Well, we are down to some rudimentary basics here.
in no particular order.

First, IS IT ACTUALLY OVERHEATING? How hot does it get? No guesses. Actual temperature measurements on a good gauge.

Second, if a hose is sucking flat, replacing it is NOT the answer. It needs a SPRING inside of it. Make one out of a coat hanger wrapped around a broom handle.

Third, the coolant bypass should be open. You cannot run a plugged bypass type water pump with a thermostat.

Fourth, if driving down the road faster than 35 does not cool it, then airflow is NOT the problem.
Unless-----the radiator is tiny

Fifth, Or there is insufficient water flow. Plugged radiator? If in question, then have a radiator shop flow check it in gallons per minute free flow.
Try running your heater full blast and see if this helps. It is a little radiator.

Sixth, The water pump MUST be overdriven. The water pump pulley must be smaller than the crankshaft pulley. period. Hopefully 20%.

Seventh, a coolant gas analyzer might be needed to test if combustion pressure is leaking into the coolant. Blown head gasket.

Eighth, SBC head gaskets are symetrical.

Ninth, very bad ignition timing is a possible overheating problem. Also detonation.

Tenth, Also heads that have been hog-ported and the metal is just too thin and is transferring heat too rapidly, and the radiator is not big enough to handle it.

Eleventh, bad radiator cap. TEST it. make sure it holds at least 16#.

Twelveth, pullies designed for standard rotation have a different bolt pattern than reverse rotation.

Last edited by ScoTFrenzel; 01-11-2009 at 03:03 PM.
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Old 01-11-2009, 03:50 PM
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Quote:
Originally Posted by beast10
Ok I have viewed all the post on over heating engines and have done pretty much everything that was recomended. Ok about my engine, is a 350, with a brand new water pump, thermastat,raidator,hoses, new cap, no leaks, oils clean not milky, engine has lots of power, timings correct, fuel mixtures good. It has headers, victor jr intake, average cam, average carb. Ok what it does is no mater if fan is on or if thermastat is in it will rise in temp until it is cut off. Driving or sitting still has no effect. Everybody i know is stumped and the only thing ive yet to do is check to see if the head gaskets are on wrong. So any ideas whats going on.
It sounds like not enough radiator. So the first set of questions go to what is the radiator and what is the vehicle?

Next question is the 350, is this a new to you or to the vehicle engine or is it an engine that didn't have problems in this installation that is now acting up following a new water pump or other hardware changes to the installation?

Lastly, what is the configuration of the heater hose and engine coolant bypass, Chevy small blocks get weird when this isn't correct and what is the thermostat in it there, and what temperature does it open?

Bogie
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Old 01-11-2009, 03:51 PM
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by pass pump?

Quote:
Third, the coolant bypass should be open. You cannot run a plugged bypass type water pump with a thermostat.
Scott, what is a bypass type water pump? Is stock SBC pump a bypass pump? This is the first i've heard this term.

Thanks!
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Old 01-11-2009, 03:57 PM
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Quote:
Originally Posted by beast10
.... Both hoses get hot....
Are you running a heater, if so there should be 4 hoses not just 2. My point is if you are not running a heater & you have an "incurable" heating issue, chances are you have a water pump that needs the heater routing to perform properly. Connect the two heater ports together to allow the flow the motor needs. It's not common but some vans had a pump like that & some late 50's motors had it aswell.
We have encoutered it at our shop a few times.
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Old 01-11-2009, 04:03 PM
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Quote:
Originally Posted by MorrisonLC
Scott, what is a bypass type water pump? Is stock SBC pump a bypass pump? This is the first i've heard this term.

Thanks!
Since I'm still on this hopefully Scott won't be too upset if I jump on this. Chevy's use a bypassing water pump which is located on the right (passenger) side. There is an extra hole of about 1/4 to 3/8s of an inch below the large outlet into the block. The small hole connects to a passage back to the head about in the middle of the block deck in front of the cylinder. This passage goes thru the pump till it comes out on the coolant intake side of the impeller. It provides a coolant flow path within the engine when the thermostat is closed so that local internal boiling of the coolant doesn't occur and the pump impeller doesn't cavitate.

To go further, the SBC is sensitive to heater routing. This is also a bypass circuit. It loops coolant from just before the thermostat with a hose off the intake coolant return, passes it either thru the heater core or if the vehicle has AC, thru a bypassing on/off valve, then the coolant routes back to the inlet side of the pump either by a fitting on the top of the pump or back to the suction side tank of the radiator. Many Chevy installations are not happy if this thing isn't functioning.

Bogie
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