How hot do Big Blocks normally run?

[SavageC20]

I have a 454 in my 72' and it gets warm in the summer (200-230) when the truck is sitting at stop lights or driving slowly (0-40mph). I am wondering if this is too hot for the engine? It has never boiled over in this situation. I have heard that big blocks run hot, but not sure what "hot" is. In the winter the temps stay around 180-190. How hot should a big block run with an ambient air temperature of 90-110 degrees? Any ideas on how to make it run cooler? I am wanting to take this truck in the mountains in the summer, but I don't think it would be able to pull a grade without getting north of 230 degrees.

The truck has a new 4 row stock style radiator from LMC, new stock water pump, new thermostat, stock fan and fan shroud, new fan clutch, 16lb radiator cap, 50/50 coolant mix, and the cooling system is clean. Temperature probe is located in the intake manifold near the thermostat housing, it goes to a VDO mechanical gauge. Carb is tuned properly and timing is set at 34 degrees total...vacuum advance not hooked up.

The truck still has the factory A/C condenser in front of the radiator as well as a transmission cooler in between them. This may be affecting airflow, but minus the transmission cooler this is basically how it was from the factory.

[rjs53]

I know the newer motors run around 210-220, but I always try to keep my 1st gen small and big blocks under 200 degrees. Not sure exactly how hot they can run though without overheating.

[geezer#99]

I rode in a 70 Vette in Reno back 30 years ago. The gauge hit 245. It was nerve racking.
With 34 total timing there’s a chance you only have 8 initial.
More initial will help it run cooler.
You could try plugging your vac advance back up to a manifold vac source.

[SavageC20]

Originally Posted by geezer#99

I rode in a 70 Vette in Reno back 30 years ago. The gauge hit 245. It was nerve racking.
With 34 total timing there’s a chance you only have 8 initial.
More initial will help it run cooler.
You could try plugging your vac advance back up to a manifold vac source.

I should have listed the initial timing as well. I have it set at 12 or 14 degrees I believe.

I was running the vacuum advance and it didn't change anything.

[geezer#99]

So that means you have 20 in the distributor.
Maybe!
At what rpm is your timing all in?

[SavageC20]

Originally Posted by geezer#99

So that means you have 20 in the distributor.
Maybe!
At what rpm is your timing all in?

No idea to be honest. I had my machine shop break in the engine so I would have no liability if anything went south. They set the timing during this process. I know on the invoice it said 34 total, but I don't have the invoice in front of me to be sure of the exact initial timing so I am going off memory....

[Mike C]

Here is a link to a thread that will help you. There are more. Lars on the CorvetteForum is great and and this thread has a copied article from John Hinckley. Too much to retype here.

https://www.corvetteforum.com/forums...heating-2.html

[72c20customcamper]

My BBC runs at 190 most times but my fans come on at 195 most time it's when I'm in traffic. These are head temps if your running that hot at the manifold it's too hot . New engines are designed to run hot to help emissions. If you have a thermo clutch check it it's possible it's not coming on .

[SavageC20]

Originally Posted by 72c20customcamper

My BBC runs at 190 most times but my fans come on at 195 most time it's when I'm in traffic. These are head temps if your running that hot at the manifold it's too hot . New engines are designed to run hot to help emissions. If you have a thermo clutch check it it's possible it's not coming on .

I have a new fan clutch that is functioning properly, but it is the standard duty variant. I have thought about getting a heavy duty or severe duty...do you think that would help?
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[engineer_gregh]

Thats too hot IMO. My 402 is bored .30 over and I had the same problem as you. I added two 1600 CFM electric pusher fans on a stock 4 row radiator that kick on at 185 and off at 165, solved my problem. Mine don't get above ~190 even in the summer with the A/C on. No more mechanical fan for me.

[weq92f]

Originally Posted by engineer_gregh

Thats too hot IMO. My 402 is bored .30 over and I had the same problem as you. I added two 1600 CFM electric pusher fans on a stock 4 row radiator that kick on at 185 and off at 165, solved my problem. Mine don't get above ~190 even in the summer with the A/C on. No more mechanical fan for me.

I'm interested to know where your senders are located for the fans/gauge, what therm-o you run.

I have my fan sender in the therm-o housing and the gauge sender in the intake right at the driver head... gauge hangs around 200-210 on hot day at idle with AC blowing and fans running. Fans are set to on=195 off=185. Must be about 10* diff between these two senders or their locations.

-klb

[72c20customcamper]

Originally Posted by Steeveedee

I have a 180° thermostat, but pulling a hill with my travel trailer the engine has gotten up to 260°, which is about as hot as would be allowed.. It helps that there is no air in the system and I had a good cap. I don't like it, and went to a truly heavy duty fan clutch, but haven't taken the trailer out for a camp out since I put that clutch on.

Originally Posted by weq92f

I'm interested to know where your senders are located for the fans/gauge, what therm-o you run.

I have my fan sender in the therm-o housing and the gauge sender in the intake right at the driver head... gauge hangs around 200-210 on hot day at idle with AC blowing and fans running. Fans are set to on=195 off=185. Must be about 10* diff between these two senders or their locations.

-klb

I use a mechanical temp gauge in the head . The sensor is in my radiator for the fans only one ,it grounds at 195 and starts the fans and opens at 185 stopping the fans .

There is a 10 to 15° difference between head temps and temp of the water. So if your running 200 -210 at the water housing in the manifold your head temp will be much higher.

My fans kick on when the head temp reaches 205. But the water temp measured buy both an instant read thermopen and a thermoworks infrared themo is 195.

[Steeveedee]

My temp gauge is manual, with the bulb in the head. I know from long standing experience that 260F won't kill a BBC quickly. But I still don't like it, of course. It just tends to age the equipment faster than I like. It's up for rebuild, anyway. It's been 110k miles since the last rebuild, is using oil, and the pressure drops to 20 PSI when it's good and hot.

[RustyBucket]

My 2wd Blazer has a mild 454 +.40, 236 peanut port heads, Performer RPM, headers... and runs COOL. Idling a long time on a hot Florida day it won't go over 190deg. At road speed it drops back down to 160. Factory gauge with the sender in the intake. It has a 4 core GM radiator, factory shroud, 7 blade clutch fan, aluminum water pump and an A/C condenser in front of the radiator(don't use the A/C 'cause I never put the top on). I haven't had a timing light on it in years but it seems to run best advanced 'til it bucks against the starter and backed off a little.

[clay68c10]

I'd say you're running a bit warm. If you had operational AC, I bet it would put you over the edge. Same with pulling a grade.
My previous 68 had a 030 over 454, 195 stat, and a Lincoln MK8 electric fan. It would hold steady at 200-205 in TX summer with the AC on and in traffic.
I think the fan was the key for me.

[alsriv2]

My BB396 was built professionally 7 years ago. (Shown in profile picture) We finally got the truck up and running just last year after much work. The truck has a 3 core radiator, a fixed fan with no shroud and always runs cool, even here in the SE Arizona desert. The heads are from a '71 402, meaning they are not the small peanut port heads. We actually had to add a 180 thermostat as the Holley Sniper control system did not like the cool temps. It was nothing to see the truck at 80mph/3000rpm stay cool at 160deg. The Holley system is a bit happier now, but the TQ converter is all wrong for the Cam installed. That will be the next item I have to fix. I wish I could give better details on timing and such, but we have it set for the builders dyno setup at 34 all in. Per the builder, I am NOT running vacuum advance, we are running a full MSD ignition that is also tied into the Sniper control system. TO say that I am happy after 7 years of pain would be an understatement.

[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.