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Old 06-16-2006, 02:24 PM
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engine running hot after cam change

I had a .510 Comp cams cam in my 355 and the temp was normal but it ran like a terd because i missmatched a bunch of parts so I put in a 268H comp and put on a performer rpm intake instead of the Victor Jr. The engine performes alot better but the temp is always a needles width below 210. Before the cam change it never got above 185. I have a 180 thermostat in it. Also, the radiator seems to only want to stay half full. I'll fill it up the rest of the way but then it just dumps it back into the overflow catch can. The coolant I'm using is the Orange GM stuff, now my buddy tells me i can't put that in my engine because it's an pre-86 block and has double hump heads. I do have flat top pistons and am hoping that the compression isn't to high and is boiling the fluid out. Never overheats, just wants to run at 210. Any thoughts would be appreciated. 83 K10 Silverado Thanks, Sam

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Old 06-16-2006, 02:58 PM
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With the smaller cam, you may now have more compression, giving you a heating problem. With more duration and overlap on the bigger cams, compression is bled off to a degree. With a smaller cam, the bleed off of compression goes away and you can end up with more compression. 210 is not bad, just watch it carefully and maybe change the antifreeze and install a new 15 pound cap.

Mark
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Old 06-16-2006, 03:49 PM
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A 10:1 cr 355 with a compcam 292H will have a dynamic compression ration of about 7.46:1

A 10:1 cr 355 with a compcam 268H will have a dynamic compression ration of about 8.17:1

Quite a bit of difference there between the two cams. Later closing point of the intake valve is the reason for reduced cylinder pressures (not overlap).

Make sure to use a 50/50 mixture and may be try a new and stronger cap.

Last edited by 454C10; 06-16-2006 at 03:55 PM.
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Old 06-16-2006, 04:58 PM
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What intake manifold gaskets did you use?

tom
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Old 06-16-2006, 07:09 PM
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Quote:
Originally Posted by sam83k10
I had a .510 Comp cams cam in my 355 and the temp was normal but it ran like a terd because i missmatched a bunch of parts so I put in a 268H comp and put on a performer rpm intake instead of the Victor Jr. The engine performes alot better but the temp is always a needles width below 210. Before the cam change it never got above 185. I have a 180 thermostat in it. Also, the radiator seems to only want to stay half full. I'll fill it up the rest of the way but then it just dumps it back into the overflow catch can. The coolant I'm using is the Orange GM stuff, now my buddy tells me i can't put that in my engine because it's an pre-86 block and has double hump heads. I do have flat top pistons and am hoping that the compression isn't to high and is boiling the fluid out. Never overheats, just wants to run at 210. Any thoughts would be appreciated. 83 K10 Silverado Thanks, Sam

Sounds like you've got an airlock in it to me, but it could be something else.

Did you remove the thermostat and fill the block, then put the thermostat back in? I also top mine off by removing a heater hose and using that as a vent while I fill it.

Do make certain you have the correct intake gaskets, and make sure you don't have the timing too slow. Retarded ignition timing makes an engine run hot.


Brian
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Old 06-16-2006, 11:05 PM
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Could try a 160 stat.I don't like my engines much over that anyways.
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Old 06-17-2006, 07:15 AM
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I did fill it up through the thermostat hole in the intake but it does seem like I have some sort of air lock. If I was boiling the fluid my temp would be higher than 210, right. But if my cap is bad then it could be boiling at a lower temp. I used Fel-Pro gaskets, can't remember what number but they ain't blocking any holes if that's what your getting at. The radiator only ever staying half full has got to be where my higher heat is coming from. I'll try a new cap and if that doesn't work maybe a 170 thermostat. Going to be 90 up here today, should put it to the test.
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Old 06-17-2006, 07:58 PM
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I just fire my engine up without the radiator cap on and let everything circulate for awhile and that gets the air bubbles out. My radiator is higher than my engine which allows the air to escape there. If for some reason parts of your engine are higher than your radiator, there is a possibility of air becoming trapped in those areas.

Kits are also made that you can clamp on where your radiator cap goes that will fill the radiator with fluid as air pockets are displaced.

210 isn't a bad temperature. I wouldn't want my engine much over that, but the engine does need to get hot enough to sufficiently burn off oil contaminents.
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Old 06-18-2006, 04:55 AM
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The overflow of the radiator sounds like a head gasket problem. If you fill the radiator and then watch the coolant level with the water pump belt removed.
You should not see any bubbles or changes in the water level. Do this on a cold engine for a short time.
Bob
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