How hot do Big Blocks normally run?

[WorkinLonghorn]

Originally Posted by SavageC20

Thank you for the advice.
The reason I disconnected it is because the guy that tuned it at the machine shop said not to run it. I trusted his judgement, but I will hook it back up and see if it changes anything.
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Well, I don't know why he advised this. The GM engineers (and EVERY other manufacturer) thought it was necessary. It gives you MUCH better MPG fuel economy in a cruise situation (freeway) and any other part-throttle driving situation and with a BB, unless you own a gas station, this is important! As you know, it does not effect idle or full throttle timing, just light throttle opening. It will lower the heat generated during light throttle. I would definately make sure it is functional and hooked up.

With a stock fan and the AC condenser and the other cooler all in line for the air flow, maybe you will idle a little warm but after you hit road speeds I think you should be OK. Is that condenser in good condition without a lot of bent fins?

[SavageC20]

Originally Posted by WorkinLonghorn

Well, I don't know why he advised this. The GM engineers (and EVERY other manufacturer) thought it was necessary. It gives you MUCH better MPG fuel economy in a cruise situation (freeway) and any other part-throttle driving situation and with a BB, unless you own a gas station, this is important! As you know, it does not effect idle or full throttle timing, just light throttle opening. It will lower the heat generated during light throttle. I would definately make sure it is functional and hooked up.

With a stock fan and the AC condenser and the other cooler all in line for the air flow, maybe you will idle a little warm but after you hit road speeds I think you should be OK. Is that condenser in good condition without a lot of bent fins?

The condenser fins are in good shape and there are no bugs in it. I spoke with the guy at the machine shop regarding no vacuum advance causing retarded timing at part throttle applications, he agreed. We are going to put an adjustable vacuum advance canister on it and get it dialed in.
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[SavageC20]

Originally Posted by SavageC20

The condenser fins are in good shape and there are no bugs in it. I spoke with the guy at the machine shop regarding no vacuum advance causing retarded timing at part throttle applications, he agreed. We are going to put an adjustable vacuum advance canister on it and get it dialed in. I also found a severe duty fan clutch that will work. Hopefully these two items improve the cooling. I will update in a few days when it’s running again.
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[68 P.O.S.]

Working Longhorn & Mike C have it dead on. To put it mildly, the guy who said not to hook it up is a friggin' moron lol. You need the added advance the vac can provides during idle and cruise for improved cooling, mpg, throttle response, and driveability. Make sure you hook it up to manifold vacuum so it will work as originally designed. It doesn't need more than 15 degrees like stock or you'll get detonation. Get the Crane 99601-1. It's the best, most adjustable vac advance on the market. Plus it comes with the correct advance springs for your dizzy's mechanical advance to put in the right rpm range (use 1 blue and 1 silver).

[steelhorse]

I use to drive a 75 F150 with a bored out 460 10.5 compression 550 lift cam,headers ect.
I live in North Carolina and on even the hottest days never got above 210 degrees. I used a 180 t stat and a big block a/c radiator from advance.

[SavageC20]

After hooking up the adjustable vacuum advance and getting it dialed in the truck seems to run about ten degrees cooler, 185 degrees, according to my VDO gauge. I am going to install the severe duty fan clutch and see if I can get it any lower. I used an infrared temp gun and at idle the thermostat housing was reading 175 degrees and the front of the block was reading 200 degrees. Not sure how accurate the temp gun is but it seems to be close.

[Mike C]

Nice. The Corvette board is a great resource for big block issues if you are looking to dive in any deeper. Any problems that a truck might have are magnified 4x in a Corvette. Really interesting to see just how important the initial advance and vacuum are to a big block working at its best.

[SavageC20]

Originally Posted by Mike C

Nice. The Corvette board is a great resource for big block issues if you are looking to dive in any deeper. Any problems that a truck might have are magnified 4x in a Corvette. Really interesting to see just how important the initial advance and vacuum are to a big block working at its best.

I noticed that the vacuum advance is hooked up to ported vacuum. Can I just move the hose to a manifold vacuum source without having to readjust timing? Based on the corvette article they really stressed the importance of vacuum advance running on manifold vacuum only.
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EDIT: never mind it is hooked up correctly. Thanks again for all of the advice.

[SavageC20]

I installed a Hayden severe duty fan clutch (part number 2797) on the truck and it sits just a hair above 180 degrees in low speed conditions. This should help out during the summer when its north of 100 degrees. Unfortunately, the new Hayden fan clutch failed after about 25 miles...completely freewheeling. It is made in Mexico now and is probably garbage. Exchanging the one that failed to see if the next one will work. If the new one does not work I will be going with ACDelco. All in all I feel that the severe duty fan clutch is a good upgrade if it is working properly.


Here are some pics of the standard duty fan clutch and the severe duty.

[toolboxchev]

It would be interesting to figure out if that bypass hose straight back to the block has anything to do with heat transfer. Its the second big block I have seen in pics on here with it. Modern Vortec manifolds and installs have one too.

I would be wanting to put that bypass into the radiator. Curious, Anyone have any insight?

[Steeveedee]

Here is how my setup looks under the hood. I have a severe duty clutch that matches the stock clutch, as short a clutch as I could find. The fan is still inside the radiator too far. It doesn't match SavageC20's setup for where the fan sits in the radiator. First pic is straight down, second angles into the shroud. Third pic shows where the PS belt rubbed on the shroud. The shroud is up against the radiator core support as it should be. Pic 4 is the driver's side MM location (forward holes) and pic 5 is the passenger's side MM location, again in the forward holes.

[SavageC20]

Originally Posted by Steeveedee

Here is how my setup looks under the hood. I have a severe duty clutch that matches the stock clutch, as short a clutch as I could find. The fan is still inside the radiator too far. It doesn't match SavageC20's setup for where the fan sits in the radiator. First pic is straight down, second angles into the shroud. Third pic shows where the PS belt rubbed on the shroud. The shroud is up against the radiator core support as it should be. Pic 4 is the driver's side MM location (forward holes) and pic 5 is the passenger's side MM location, again in the forward holes.

Your engine is definitely sitting farther forward than mine. Here is how mine is set up. I have a little bit of fan blade sticking out of the shroud. My standard duty fan clutch was approx an inch and a half longer than the severe duty and it still had clearance between the radiator and the clutch. Last pic shows where my trans crossmember is mounted.

[Steeveedee]

My transmission cross member is mounted in the set of holes forward of where yours is, looks like about an inch. Not having had this apart, since it was rebuilt decades ago, are the left and right frame perches different? Maybe the rebuilders got them switched? I just don't know. But this is looking like the last piece of the puzzle. I can see that there is a lot of spline that could be taken up. One inch might be enough to get the fan where it belongs. I've verified that it is a big block fan shroud.

[SavageC20]

Originally Posted by Steeveedee

My transmission cross member is mounted in the set of holes forward of where yours is, looks like about an inch. Not having had this apart, since it was rebuilt decades ago, are the left and right frame perches different? Maybe the rebuilders got them switched? I just don't know. But this is looking like the last piece of the puzzle. I can see that there is a lot of spline that could be taken up. One inch might be enough to get the fan where it belongs. I've verified that it is a big block fan shroud.

I do not know if the frame perches are side specific, but I do know that my 72' frame perches are a different design than your 70' frame perches. That could be the reason why yours is set up a bit differently than mine. When you say that there is a lot of spline that can be taken up are you referring to the splines on the output shaft of the transmission?

Here are the pics of the different motor mounts/perches, first pic is what I believe you have and second pic is mine.

[Steeveedee]

As for the front drive shaft spline, yes. There is probably 5 inches exposed. I don't know what it should look like, but that seems to be a lot, to me. I worked on this truck many times before I graduated university, but never got into the engine and trans rebuilding. My FiL had that done at some point after I graduated. Do you have a pic of the other sides of the frame perches? From the picture you have there, they look asymmetric. That could just be an artifact of the camera angle.

[SavageC20]

Originally Posted by Steeveedee

As for the front drive shaft spline, yes. There is probably 5 inches exposed. I don't know what it should look like, but that seems to be a lot, to me. I worked on this truck many times before I graduated university, but never got into the engine and trans rebuilding. My FiL had that done at some point after I graduated. Do you have a pic of the other sides of the frame perches? From the picture you have there, they look asymmetric. That could just be an artifact of the camera angle.

I think that 5 inches of spline showing is probably excessive. Here is what my truck looks like. I also have a turbo 400.


I found some more pics of the factory 68-71 perches and they may in fact be side specific. These are the best pics I could find.

[davepl]

FWIW, mine is a completely bone stock 402 except it uses R-134 and has dual exhaust. Otherwise, factory down to the heat riser, choke, etc.

It will creep in warm traffic. IT's OK while rolling. But it'll eventually hit 230+ sitting at a light, so I added a thermostatic fan in between the rad and the condenser and that seems to have crutched it enough. I'd recommend the extra emergency fan.

[Steeveedee]

Not having put those pieces in, they look like they can only be put in one way. Maybe I'm wrong, there. I wasn't clear on the driveshaft. It's the spline on the rear section that has a lot exposed. Here are both sections for reference. There are more bolt holes in the cross member that the center support sits on, about 1" back. The backs of the fan blades are 3/4" ahead of the back edge of the fan shroud, so more like 1-1/2" to1-3/4" movement would be better. Most of the equipment here has slotted holes, so I should be able to massage them a bit.

Looks like I have a center support carrier in my near future, too.

Davepl- I am considering an auxiliary fan, but want the rest of this ironed out first. All this hot running is without using the AC. My truck has dual exhaust, as well, btw.

[SavageC20]

Originally Posted by davepl

FWIW, mine is a completely bone stock 402 except it uses R-134 and has dual exhaust. Otherwise, factory down to the heat riser, choke, etc.

It will creep in warm traffic. IT's OK while rolling. But it'll eventually hit 230+ sitting at a light, so I added a thermostatic fan in between the rad and the condenser and that seems to have crutched it enough. I'd recommend the extra emergency fan.

Would you be able to include a picture of your fan setup?

[SavageC20]

Originally Posted by Steeveedee

Not having put those pieces in, they look like they can only be put in one way. Maybe I'm wrong, there. I wasn't clear on the driveshaft. It's the spline on the rear section that has a lot exposed. Here are both sections for reference. There are more bolt holes in the cross member that the center support sits on, about 1" back. The backs of the fan blades are 3/4" ahead of the back edge of the fan shroud, so more like 1-1/2" to1-3/4" movement would be better. Most of the equipment here has slotted holes, so I should be able to massage them a bit.

Looks like I have a center support carrier in my near future, too.

Davepl- I am considering an auxiliary fan, but want the rest of this ironed out first. All this hot running is without using the AC. My truck has dual exhaust, as well, btw.

Heres what the rear of the front shaft looks like on mine. I also had to replace that carrier bearing on mine. Looks like you will have adequate clearance to move the whole drivetrain back a bit to get the fan lined up.

[Steeveedee]

Originally Posted by SavageC20

Heres what the rear of the front shaft looks like on mine. I also had to replace that carrier bearing on mine. Looks like you will have adequate clearance to move the whole drivetrain back a bit to get the fan lined up.

That's what I'm thinking. Also, thank you for all the pictures. I really appreciate it!

[SavageC20]

Originally Posted by Steeveedee

That's what I'm thinking. Also, thank you for all the pictures. I really appreciate it!

No problem, happy to help.

Originally Posted by Mike C

If only they had gone to my link above in post #7 they would have seen that much sooner. LOL.

Big block Corvettes run notoriously hot and those guys have the answer that can be applied to a truck. But as I noted above, the correct process is too long to retype all the darn time. Thus the link.

So true--I had an original 66 vette--427 and it would get really hot--not much air flow in those. I heard the 396s were even worse. I ended up putting an electric fan off a newer model--helped a lot. My new to me 72' K10 which I am picking up in a couple of weeks should have zero issues with the stock 350.