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Old 12-29-2001, 04:56 PM
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Question SBC 350 erratic temperature

My 350 has 3,100 miles on it since rebuild. It was fine when I bought it with 1,600 miles, this is a recent developement. So far I have replaced the thermostat, used distilled water, and put in new antifreeze. Next will be a radiator check and boil-out. I really think that I have 2 problems. My Stewart Warner temp gauge doesn't come off of the bottom peg for a couple of miles, then it jumps right to 145 and continues normal as if it is stuck or it's not sitting in water. Once it comes up to temp (180 stat), it stays at temp for about 5-10 miles. Then it goes up to about 210 and will fluctuate between 185-210. I also have a very minor leak at the back of the engine somewhere, I see a drop or 2 on the floor every once in a while. I'm not sure where water could even come from other than maybe a freeze plug behind the bell housing. Your thoughts?? Who knows, maybe the gauge is the problem with both??? Thanks

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Old 12-29-2001, 06:10 PM
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First off try a new guage. If the temp is actually fluctuating it could be several reasons bad thermostat, cracked head, bad head gasket,collapsing hose,stuck mech advance, incorect timing, lean mixture or bad carb, vacume leak,ect ect... but if the guage is acting funny I would start there. As for the leak get a cooling system pressure tester it will show you the leak
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Old 12-29-2001, 06:43 PM
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Just my 2 cents here, If it is an electonic sender, make sure you didn`t put silicone on the sender threads. The sender needs a ground to work properly. The silicone would isolate it from grounding. Then give you irratic readings.
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Old 12-30-2001, 07:20 AM
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As Ed says grounds are very important on electric gauges. DO NOT sister the grounds together under the dash for the temp gauge run a seperate ground for that gauge to a good ground. Also i dont like the idea of the sender in cyl head(if thats were yours is) i like it up in the intake were it belongs,with header heat not effecting your readings. Go see if a friend has a mech gauge you can use and check it against your electric. Pressure test the cooling system first and find the leak cause if you have a crack or gasket problem the temp gauge problem dont matter anyway its got to come apart.
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Old 12-30-2001, 08:48 AM
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what kind of 350 pontiac or chvy? I had problems with my pontiac. lots of stuff so if you want to hear about them post me back
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Old 12-31-2001, 11:41 AM
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I guess that I left a couple of important things out, it's not an electronic gauge, it has a capilary tube. Also, the sensor is in the manifold, not in the block. The timing is set for 8 DBTDC at idle with the advance disconnected. I was concidering moving the sensor down onto the head but never thought about the header heat. The thermostat has been changed twice. The hoses and pump I believe are new. The carb is a new Edelbrock (550 CFM I think) squarebore that I have messed with the idle mixture a little because the fumes in the garage are a little rough. The distributor is a new Mallory unit and the advance seems to work OK according to the timing light. Thanks for the good advice so far!

[ December 31, 2001: Message edited by: HotRodF100 ]

[ December 31, 2001: Message edited by: HotRodF100 ]</p>
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Old 01-03-2002, 07:24 PM
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First check the guage for correct temps using another guage of some type for a comparison. FIx the damn leak, it will bite you sooner or later...
As for the temp changes it has factors of ignion timing, water pump, thermostat, cooling fan, the flow of the colant, engine bore, spark plugs, loose fan belts. Most small block chevys were ment to run 190 degrees and as high as 215 degrees temp. on newer cars
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