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Old 11-10-2005, 11:04 AM
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400 Sbc running warm or not?

I am confused I don't know if my 400 is running hot or is not. The factory gauge in my 84 Monte Carlo SS says that the car is running 220. To me that's too warm. But then I hooked up a mech. temp gauge next to the thermostat and the car is running right at 195. Search here shows that it's normal for there to be a 10-20 degree variance between the two locations. However, most says keeping the water temp between 180-200 makes for good conmbustion and allows the oil to burn off deposits. Any hotter then 200 and most agree that is a little too warm (speaking for the carb'd crowd not new fuel injected car). So is my car running too warm or not? It would seem the only way to make it run cooler using the factory gauge is putting in a 180 t-stat assuming my rediator can keep the temp down 15 degrees. Then I would see about 200 give or take on the factory gauge. I guess I am a little confused. Also my sender in the head is close to my header flange. There is about 3/16" clearance between the adapter and the flange (I assume this give make it read a tad higher also).

P.S. The temp the other morning here was 42 and I had the heater on and the factory gauge still read 220. The temp seems stable and does not climb higher.

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Old 11-10-2005, 11:39 AM
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Generally you will get a higher reading at the intake than you will at the head. Sounds like your gage is not reading accurately. If the header heat is an issue. I suggest going to an electric sender. It is less likely to be affected by header heat.
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Old 11-10-2005, 11:49 AM
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Sender

The factory gauge which uses a sender in the head is electric. The aftermarket gauge which is mechanical is installed near the T-stat. I thought the heat in the head is higher because it is closer to the combustion chamber versus the intake seeing the cooler water from the radiator.
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Old 11-10-2005, 12:02 PM
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What T-stat do you have in the engine now?

Running at 220 is good in the cold weather for a strong heater! hahahaha

I had an over heating problem with a 400 a few years ago. I was working on a friends car and he didn't know he had a 400 block. And he installed a set of cylinder heads without drilling steam holes in the cylinder heads. And the car would constantly over heat no matter how I tried to cool it. We finally figured it out after many fan and radiator battles. Plus steam holes don't work if the gaskets cover the holes. You are running the drilled heads and proper head gaskets, right?
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Old 11-10-2005, 12:18 PM
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Steam holes

Yes the heads have been drilled for the steam holes. As I said the temp does not climb so it isn't overheating but the factory gauge reads 220 in the head and the mech. temp gauge will say 195. The engine only has about 200 miles on it and everything except the radiator was replaced with the new engine. Including a high flow water pump and 195 stat. The radiator has no visible deposits and the fins are in good conditioned and free from bugs, etc. So it sounds like some may think I am posting about overheating when infact I just want to know if 195 near the thermostat and 220 or a tad less at the cylinder head is normal. For those that have senders in the cylinder heads what are you temps and have you compared that to the area near the T-stat. I guess I may need to hook the mech. up at the head to see what it reads there.
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Old 11-10-2005, 12:27 PM
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Sounds like your electrical sender is off. I would go with the mechanical gage. The temperature at the stat should be the hottest point of the water. I think you are good especialy since you are running a 195 stat.
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Old 11-10-2005, 02:27 PM
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The tempature will be hotter in the head, that`s where the action is taking place, combustion is heat. In common sense heat rises, but in a engine, the most heat will be in the head and the upper part of the block, since there`s a lotta fire goin on in there as well as exhaust gas. I would place the mechanical in the head and see what reading you get, you`ll also likely notice that when it`s in the head it`ll pick up the variences faster, like when you get on it the temp will rise as much as 20 degrees compared to by the thermostat it might rise 5. 220 really isn`t all that hot, but it`s too hot for comfort since it you don`t have alot of leeway until it is running hot. Alot of things can cause to high of temps, carb too lean, vacuum leak, slow ignition timing, collapsing hoses, incorrectly filling the cooling system, etc. Since you have a carlo, and I have a cutlass that I`ve had countless heating issues with, I`ll pass this on. Do you have the overflow connected to the radiator? if you have it capped off it`ll run hotter or run hot since the system has to burp and it can`t if it`s capped. If it is connected try this, drain about 3 liters of coolant out, reinstall the radiator cap, fill the overflow to it`s fill line, start the car and let it idle, when it starts to get up to temp watch the overflow, you`ll see the bubbles come up and the coolant level go down. refill the overflow as needed. This is what I did to make mine run a normal temp after I replaced everything and it still ran hot, I found this information in the factory manual, and it worked. I had filled it before that the way I`ve always did, cap off, engine running, fill until it`s full, but it don`t work too good on burp systems these cars have.
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Old 11-10-2005, 03:48 PM
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I've got a 406 in an A Body El Camino. It runs around 190 or so with the electric factory gauge. The only time it gets to 220 is summer traffic. These factory gauges are not the finest pieces of measurement. Have you tried the mechanical in the head?
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Old 11-10-2005, 05:11 PM
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Quote:
Originally Posted by 84KYSS
I thought the heat in the head is higher because it is closer to the combustion chamber versus the intake seeing the cooler water from the radiator.
The water neck on the intake manifold is where the coolant exits the engine. The coolant travels through the block, into the heads and out the intake manifold. Any heat gathered as the coolant passes through the heads is going to be carried through the water passage at the front of the intake.

195 is fine. I have my fans set to come on at 205 so my engine cycles between about 190 and 205 when in traffic.
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Old 11-10-2005, 06:29 PM
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If your SS is a 1984........it is over twenty years old and so is the sender...
I do not believe you have a heat issue.....just a old gauge issue....

Buy a new factory GM one correct for your car.....if you can...

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Old 11-10-2005, 09:22 PM
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Overflow hose

The overflow is connected up. I can try the procedure listed to help burp the system. The sender for the factory gauge is new. This evening while doing some carb adjustments I tried burping the system again by doing the cap off and when the car got to temp or showed 195 on the mech. gauge I put a meat thermometer in the coolant at the fill neck and it went to about 160. This weekend I will install the mech gauge into the cylinder head and the factory gauge near the T-stat. Carb could be lean. I am using the stock computer and carb and the dwell was at 18 which is lean and after my adjustments I got it to 25. I'll have to do some more adjustments to get it to 30 which is suppose to be the magic number. The initial timing is 10* is that too low. I can't go much higher as the computer will add 28 total at WOT.
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Old 11-11-2005, 04:08 AM
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You probably got the 160 deg temp reading because your filler neck is more than likely going to be on the outlet side of the radiator (the tank that the water pump hose connects to). Your coolant has already passed through the radiator, which is why that reading is lower than either of your gauges. If you could somehow stick that thermometer on the inlet side of the radiator you would probably find it would read somewhere around 195-200.

As far as the electric gauge reading warm, it may not be calibrated to read the temp sender you installed in it. Or the gauge is just plain crap. What brand mech gauge did you buy? If it's a decent one I'd trust it more than the factory gauge. If you're getting 195 at the intake you're probably in good shape.
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Old 11-11-2005, 04:55 AM
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Gauge

The sender for the factory gauge was bought at Autozone. It was around $10. The mechanical gauge is made by Sun and was $16.99. I'll swap the senders this weekend and see what each says about the other location. If the factory gauge reads higher then 195 near the T-stat then that will confirm that the sender is cheap junk or the factory gauge is off.
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Old 11-11-2005, 12:11 PM
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400 sbc

what type of fan are you running, electric or clutch?
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Old 11-11-2005, 01:18 PM
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Quote:
Carb could be lean. I am using the stock computer and carb and the dwell was at 18 which is lean and after my adjustments I got it to 25. I'll have to do some more adjustments to get it to 30 which is suppose to be the magic number. The initial timing is 10* is that too low. I can't go much higher as the computer will add 28 total at WOT.
IMHO, I'd ditch that early timing control. I had several mid 80's GM's come through the shop door this year, and the tuning issues with them were 90% caused by that early system starting to go south. I'd set the base, get it running well, the next thing you know, the ETC whacked 20* out of my total, thing ran like sh1t. Reset, run well, then the ETC would randomly add 20 or 25*, then take it back out whenever it felt like it. These things were overheating, starting hard, lacking power, you name it. Easy fix was to grab a normal HEI dizzy, and if the carb is a 4 EME, trade it out for a 4 ME and tune 'er up. Made all the difference in the oned I was repairing.
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