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Old 05-11-2018, 09:39 PM   #1
airbrushguy
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Overheating!!!!!

My '71 C10 which was a 6cyl automatic until 3 years ago when I put a solid running 305 ci SBC in it has me baffled.
I took it for a substantial two hour ride up the NY Thruway and it overheated after a half hour into the ride.
Last year I put a new aluminum radiator with two electric fans that run all the time, new hoses, thermostat, water pump etc.
The engine is a stock 305 with a mild cam, headers and Edelbrock 4bbl. When I put the v8 in it, I replaced or rebuilt everything except the trans and rear but they were both cleaned, checked, new filter in trans and trans lines and both refilled. 50/50 antifreeze in rad.
The engine would run ok if you did not push it past 50mph, at 60 it does about 3000rpm and that would immediately bury the temp gauge. The engine was truly hot, you could not touch the top hose and when I did use a rag to grab the hose and squeeze it, it was full of pressure.
Truck runs fine around town but was not put to long hi way driving until last weekend.
Any thoughts?

Thanks
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Old 05-11-2018, 09:53 PM   #2
rsavage
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Re: Overheating!!!!!

Is it boiling over and pushing antifreeze out the overflow? If not, how do you know it is over heating? Did you check water temp and gauge with a thermometer? Any blockage in the exhaust system, i.e. crushed pipe? Did you put a new radiator cap on when you changed the radiator? Are the electric fans on the front of the radiator or behind? What stat do you have in it? You can put a 160 degree stat in it. If you are running down the highway, your fans shouldn't need to be running as the air is already blowing through from movement. 3000 rpms for an extended time will create some heat.
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Old 05-11-2018, 09:55 PM   #3
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Re: Overheating!!!!!

What’s your timing like?
Retarded timing makes heat.
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Old 05-11-2018, 09:59 PM   #4
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Re: Overheating!!!!!

Right. Find someone with an infrared gun and verify the temperature. A pressurized hose doesn't tell much. I had an indicated high temperature which turned out to be the gauge. The engine wasn't all that hot, but the needle was pegged. Generally, though, at highway speeds, if it overheats (as mentioned- puking coolant), it is a clogged radiator.
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Old 05-11-2018, 10:12 PM   #5
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Re: Overheating!!!!!

Not puking antifreeze, 160 thermo, radiator less than 1 year old, new cap, did not have my infrared gun with me but engine bay was definitely hot as soon as hood was opened. Ne temp gauge sending unit. Timing 8 BTDC
Fans are pullers, behind the radiator.
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Old 05-11-2018, 10:19 PM   #6
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Re: Overheating!!!!!

Bump your initial up to 14.
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Old 05-11-2018, 10:24 PM   #7
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Re: Overheating!!!!!

Might not be overheating at all if I read you correctly.
A stock '69 350 came with a 195° thermostat that would be fully open by about 205-210°. I don't know about 305s but the engine bay will be hot and there will be pressure in the hoses. It's a pressurized system!

I would say that you should definitely get a temperature sender set up, or buy a lazar thermometer to check it with (I got one on Amazon for around $20 I think it was.

Are you hearing some bad noises, knocking etc.? -BA
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Old 05-11-2018, 10:26 PM   #8
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Re: Overheating!!!!!

Isn't stock timing 6-8° btdc ?
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Old 05-11-2018, 10:28 PM   #9
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Re: Overheating!!!!!

No noises, I'll take it back to hi way and bring thermo gun
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Old 05-11-2018, 11:12 PM   #10
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Re: Overheating!!!!!

Quote:
Originally Posted by airbrushguy View Post
Isn't stock timing 6-8° btdc ?
Might be but your motor isn’t stock anymore!
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Old 05-11-2018, 11:50 PM   #11
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Re: Overheating!!!!!

For my 70 350 stock timing was 0 and it never overheated. At 60 mph you don’t need the fans as airflow is more than enough. My thoughts are either an undersized rad , blocked cooling system, blocked exhaust. A lower temp thermostat will not let an engine run cooler it only sets the min temp. Sb chevys really run best right around 200 degrees. You could have a carb problem. To rich at 3k can cause the engine to run hot

Good luck
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Old 05-12-2018, 07:00 AM   #12
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Re: Overheating!!!!!

I had another thought. Are either of your radiator hoses collapsing thereby restricting flow?
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Old 05-12-2018, 07:28 AM   #13
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Re: Overheating!!!!!

I'd change the radiator cap again, especially if autozone part quality. Sometimes they can be bad. Possible that you have a bad thermostat and it fails closed. I'd swap the cheap stuff first. 99% of the time for me it's the simple stuff
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Old 05-12-2018, 08:50 AM   #14
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Re: Overheating!!!!!

I know you have dual fans, but do they cover the radiator? Even though they are pulling, if they aren't shrouded they wont work efficiently, causing it to overheat. To much timing will cause an over heating also, so be careful there too. Cooling seems to be the hardest thing to get the older gen one engines to do. Usually a big clutch fan and a shroud to match does it, but the electric fans should do the same job more effectively. You can have the biggest radiator they make but if your only using part of it, it wont do its job.
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Old 05-12-2018, 12:50 PM   #15
airbrushguy
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Re: Overheating!!!!!

radiator hoses are not collapsing, dual fans are new, pullers with shroud on radiator. Cap is brand new, flipper relief type.
Fans are set to run all the time, in the winter I remove one of the relays for better heat.

Last edited by airbrushguy; 05-12-2018 at 01:57 PM.
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Old 05-12-2018, 12:58 PM   #16
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Re: Overheating!!!!!

Doesn't sound too likely, but it could be a sign of a blown head gasket. Are you sure you don't have any air in the cooling system? Only time I've had overheating like you describe I had a bad brand new rad cap, a fail close thermostat (overheated quicker tho) and a bad temp sensor.
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Old 05-12-2018, 02:14 PM   #17
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Re: Overheating!!!!!

What year water pump did you put on the motor when you replaced it? Could be you installed the wrong rotation pump
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Old 05-12-2018, 05:05 PM   #18
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Re: Overheating!!!!!

Like Knight72 said, could be air in the system. Also, the hose can be collapsed and you not realize it.
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Old 05-13-2018, 03:21 AM   #19
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Re: Overheating!!!!!

One rule i tell any one that drives these trucks always have a working heater.You be amazed at how much heat is pulled from a over heating engine.From 260 degrees 30 sec is a life time.It will drop it by 70 degrees.

I don't car what wheels i have or thye body But my must haves over rims music or a clean looking motor is My brakes done right my steering right all my fuel being tight and not leaking.An a heater that works.

These are thing i know ever one of them trucks have unless you have the smart ones that remove it and there on the side of the road frying on a hot day
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Old 05-14-2018, 12:22 PM   #20
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Re: Overheating!!!!!

Sometimes if you put too cold of a t-stat in there, the coolant doesn't stay in the radiator long enough to get cooled off. It just keeps cycling the hot coolant.
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Old 05-14-2018, 01:36 PM   #21
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Re: Overheating!!!!!

is the belt tight?? slipping at the higher rpm?? Are you sure your fans are staying on at all times?? not cutting out at a certain rpm?? Voltage issue?
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Old 05-14-2018, 02:26 PM   #22
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Re: Overheating!!!!!

you gotta get a real fan.......... all those electrics are junk, go 160-180 quality thermostat and a 6cyl manuel trans has 3.73 gears hence the hi rpm,s. that 305 has thin casting heads and they crack super easy when you get them hot
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Old 05-14-2018, 10:46 PM   #23
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Re: Overheating!!!!!

Quote:
Originally Posted by BCOWANWHEELS View Post
you gotta get a real fan.......... all those electrics are junk, go 160-180 quality thermostat and a 6cyl manuel trans has 3.73 gears hence the hi rpm,s. that 305 has thin casting heads and they crack super easy when you get them hot

All electric fans are not junk, otherwise they wouldn't come standard on almost every vehicle made today. You may have bought junk fans in the past, but that doesn't mean all of them are junk.
Dual electric fans with a good shroud will move way more air than a standard clutch fan.
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Old 05-14-2018, 11:56 PM   #24
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Re: Overheating!!!!!

I have subscribed to this thread and am interested in the outcome. Good electric fans can have a problem getting enough power. Electric fans came about because of sideways mounted engines in front wheel drive cars where it is difficult to have a mechanical fan. I had a Pontiac Grand Prix with an intermittent overheating problem. It had the factory dual fans. Everything was in order. Several mechanics failed to find out why it kept overheating. In my case it was usually in stop and go traffic when it was the worst. Air conditioning performance was also intermittent, and mechanics unable to diagnose. This went on for a year and a half. One day, the starter was a little sluggish and I thought since the battery is old let's go ahead and get a fresh one. Completely, and I mean 100%, solved the intermittent overheating and air conditioner performance. The battery never showed even the slightest lack of performance starting the car until that day before I replaced it. I'm not saying it is the battery, but you do need to consider things that you may not think are closely related.
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Old 05-15-2018, 02:03 AM   #25
BCOWANWHEELS
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Re: Overheating!!!!!

Junk, just get a real steel fan with a thermo clutch and be done with it is my opinion
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