My temp goes way up during idle (at 230 it is still climbing)but is fine at crusing speed(abut 185-190)

I have just rebuilt a 396 (now a 402) in a 67 chevelle. I have an alumitech radiator with a 7 blade fan and a shroud. I have a mild Comp cam with Hooker super comp headers, 12 bolt 355 gears; stock 215 heads. 10 compression ? short edelbrock aluminmum water pump

Taking this one step at at time:

I have flushed the alumitech radiator removed the Dex-cool and went with a 30% mixture of Prestone long life(recomended by Don from Alumitech). I live in Northern California so I don't have to worry about freezing temps. I always run 93 fuel

The distance between the new fan clutch and the radiator is 1 1/2 inches

I do have a B&M tranny cooler, and I have it bolted to the front of the radiator support but it is about 2 1/2 inches from the alumitech radiator

The next thing I installed was a Hayden HD thermal fan clutch 2747 and after that set timing advanced at about 16

I know everyone talks about how great the alumitech radiator is but I really think that is the problem.


Here are some pictures:(pictures were taken before installation of Hayden clutch

http://s726.photobucket.com/albums/w...eaux/chevelle/

Thanks for any input,

Gary

You didn't mention enough about timing...
What is your intial and total without and then with vacuum advance hooked up?

How far are the blades into the shroud? I ask because my temps at idle dropped a bunch when I replaced the shroud. Previous shroud completely enclosed the fan blades, with the new one they're half in, half out.

Really kind of sounds like your fans not moving much air. Out of curiosity which way is it moving air?

With the fan being that close to the radiator I wouldnt think the shroud would be make or break.

fan needs to be half in and half out of the shroud opening to properly work. To close to the radiator and all your doing is cooling the area the fan is covering, leaving a large circuliar hot spot.

had same symptoms with my car 2years ago (450 hp 530 trq iron heads 10:1 stock water pump). was a bad Mr. Gasket thermostat. Took it out and tested it in heated water and it was not opening. Put in a new one (after I tested that one too) and no more problems. Never over 180* since. Just an idea and its easy to check. Hope you figure it out.

The distance between the fan clutch and the radiator is about 1 1/2 inches, so the fan is about half way into the shroud.

I will double-check the timing and report back

had same symptoms with my car 2years ago (450 hp 530 trq iron heads 10:1 stock water pump). was a bad Mr. Gasket thermostat. Took it out and tested it in heated water and it was not opening. Put in a new one (after I tested that one too) and no more problems. Never over 180* since. Just an idea and its easy to check. Hope you figure it out.

I second the idea that the t-stat isn't opening.

The distance between the fan clutch and the radiator is about 1 1/2 inches, so the fan is about half way into the shroud.

I will double-check the timing and report back

Just for clarity, Does that mean the fan is centered within the shroud or that the fan blades are half in and half out of the shroud opening?
If you look down at the shroud opening, you should be able to see about the back half of the fan blades outside of the opening. If the fan is in the shroud too deep, it will circulate air around within the shroud instead of pulling it through the radiator.

I could be wrong, but I would think a non or partially opening 'stat would cause overheating at road speed, where the engine is creating more heat. Overheating at idle is usually an airflow issue over the radiator.

Exactly tom... Well said

I probably misspoke; The fan blades are more in the shroud than out

regarding the timing:

16 deg advanced seems too much; 38 total?? What was stock??? My engine is not stock with a roller Comp cam (Although its mild, I could find the specs)


Here is a link to some pictures

http://s726.photobucket.com/albums/w...eaux/chevelle/

Look at the ones that say "Cooling at"

For some reason the link to the pictures isn't working. I am not sure why

Having the fan 1/2 in, 1/2 out of the shroud is as DEEP as you want to go.

Given a choice, I want a fan 1/3 in, 2/3 out.

Checked the timing;

It was advanced by 10 deg, so I advanced it to 14 with about 34 with vacuum advanced off

It most certainly not the radiator. If it cools fine at normal highway speeds, then the rad is fine. Most likely a lack airflow through the radiator at idle. Is your vac advance operating properly? Retarded timing usually causes high temps at low rpm's, not advanced. A non-operating vac advance can raise operating temp at idle. It does not make sense that the T-stat could be the problem, as it would cause overheating at highway speeds as well.

You can also check to assure that you are not using an underdrive crank pulley. People will use them to save HP at high RPM's, but they can kill you at low engine speeds. Alternators will not charge properly, water pumps do not flow enough, and fans do not turn fast enough. They are great for racing, but do not belong on daily driven street cars.


Regards, John McGraw

hey i hope you find a cure soon. but i went through a similar problem with my 67 when i rebuilt my motor. i have an aluminum radiator as well. but at stand still it didnt like to keep cool. im not sure what temp thermostat u have but i changed mine from 180 to 160 so i get the coolent alil faster and i added electric fans with no shroud. and whenever it starts to get hot i just flick the fans on and it cools it right down to 180 and highway temps sticks at about 170. if you have room i would definitely recommend electric fans. (couldnt see the pics so dont know if you do or not) but also i dont know how those work with the trans cooler there either. but wish you the best of luck. let us know how it turns out

Gary,

Just another thought. Do you have the heater bypassed? If so, do you just have the heater hose connections looped or are they plugged off? If the heater ports are looped, it can steal enough water at low engine speeds, the not enough water circulates through the radiator. You should always plug the taps if not using the heater.


Regards, John McGraw

I had the same problems with my 402,until I changed to an aluminum radiator and a high flow Stewart water pump.I also added a thermostat with the 3 bypass holes (3/16 diameter holes)Stewart thermostat.The car rarely gets over 180, and the electric fans that I added to fix the original problem never turn on now.

Thanks for the replies

I have a 180 T stat that I know is working; Its brand new and I see the temp gauge drop when it warms up

I think the vacuum advance is working properly, how do I test it?

I will check the underdrive crank pulley

The heater core is not bypassed; I bought a new heater core and it works fine

The timing is definetly advanced, now to 14 deg. 34 total;

I have a high flow edelbrock water pump

The fan blades are more in the shroud than out

Having the fan 1/2 in, 1/2 out of the shroud is as DEEP as you want to go.

Given a choice, I want a fan 1/3 in, 2/3 out.
Get a shorter fan clutch, pull the fan away from the radiator a bit more. Get the fan mostly OUT of the shroud. There's a reasonable chance this is your only problem causing the overheating.

I think the vacuum advance is working properly, how do I test it?
Suck on the hose attached to the vacuum advance, either with a vacuum pump or (ick!) with your mouth. Put your finger under the advance, so you can feel the steel rod leading into the distributor. As you draw vacuum, the rod should move. When you block the vacuum, it should not leak down.

Then test your vacuum source. Run the engine, there better be vacuum to the advance hose. Manifold vacuum will be there at idle and part throttle; ported vacuum won't be there until you crack the throttle.

"I" would be wanting manifold vacuum in this case. Change the vacuum port if needed; and re-set the idle speed.

I think I have figured out this problem.

It was cool and windy last night but I let it idle for about 15 minutes and it never got above 200.

My vacuum advance was connected to ported vacuum on the carb

so, I tee'd off the tranny vaccum hose. I have a Th400 and I was hoping shifting would not be adversely affected. It seems to be ok but this is probably not ideal.

What other choices are there? Creating a new port in the intake?

so, I tee'd off the tranny vaccum hose. I have a Th400 and I was hoping shifting would not be adversely affected. It seems to be ok but this is probably not ideal.
You're fine as-is with the vacuum advance plumbing.

Still want to pull the fan out of the shroud some more.

Good with the vac adv to full int vacuum which can in some cases lower idle temp some esp when base timing is retarded to begine with which BTW yours still is .

With a perf cam your timing at 14 deg bse/34 total is still somewhat retarded.

Try 18 deg base & 38 total and see how the motor responds to that power & temp wise.

Also,if mech adv is comming in late like 3k rpm or later and your running gear like 273-308 the motor will not reach high enough rpm when at cruise to get full mech adv making timing even more retarded too.

So with that in mind check to see at what rpm the mech adv in dist is fully in for full totaltiming not inc vac adv.

Use 93 oct fuel to help stop detonation when running a full ign timing curve like this.

Let us know how that works out.

Scott

Your fan is not installed on fan clutch backwards is it (blades wrong way)? I have seen this in the past at a car show.