Hot Rod Forum banner
Status
Not open for further replies.

396 BBC Overheating !

12K views 22 replies 8 participants last post by  Rickracer 
#1 · (Edited)
Here's the thing i'we recently put a 396 BBC into an old Jeep CJ-5 and now i'm into some heating problems.

I took it out for alittle spin yesterday in the snow ! and i couldn't drive it for more than 5 minutes than i was in some deep overheating problems, the gauge ran with the same phase to 220° F !!! this was after i put in the engine a 180° thermostat and connected the heater. right now i'm suspecting the heater core to be leaking but i have to take it out and inspect it.
After this I took the thermostat out and blocked the heater, and it was better, but still went to 195° F and stayed there, but all i drove was a short distance, maybe 3 miles :sweat: In my opinion that's a bit on the high side because there is no thermostat.

The engine is a 396 BBC 0.60" over
10.5:1 compression
990 rectangular port heads 2.19"/1.88" they are ported.
Solid roller cam 254° @.50" .644" lift.
Performer RPM manifold.
Quick fuel 850 cfm race carb.
Msd Pro Billet distributor with locked out timing at 37°
Msd Digital 6 plus ignition box.
Moroso mechanical aluminum water pump.
14" electric fan on the radiator.
3 row radiator, not sure from what it is, BUT i had a mild 350 Chevy in the Jeep and there were no cooling issues at all !!! in fact it ran too cold.

Please feel free to ask questions if i wasn't too clear on the details.

Best regards.
 
See less See more
#4 ·
Has this overheating been going on since you performed the install or is it a new problem?

Replace the thermostat and be sure it is installed correctly.

I suggest that for street use you do not run a locked out timing. Use a vacuum advance with it connected to a full manifold source.

Timing can greatly affect the temp of the coolant. Retarded timing will cause the rapid rise in temps you are seeing.

Check for any hoses disconnected that could cause a large vacuum leak. This would cause a very lean condition which would cause a rapid rise in operating temps.

Try running the electric fan constant when the ignition is on. I have found that oftentimes the thermostatically controlled electric fans will not turn on when they should.

Replace the radiator cap. It should be about a 16 psi rating.
 
#7 ·
There's flow through the radiator, and the lower hose is not blocked, The tranny is TH350 with 2500 rpm stall converter, the tranny cooler is not attatched through the radiator.
I've had this problem since the first drive, about a week ago...
If i would have vacuum leak wouldn't the engine run rough and crappy ? it run's solid idle at 1100 rpm when hot.
The fan is on when the ign switch is on.
Today i suspected that there was air on the system but after taking the cap off the radiator (highest point) it stayed the same :(

Best regards.
 
#10 ·
monzter said:
I've had this problem since the first drive, about a week ago...
If i would have vacuum leak wouldn't the engine run rough and crappy ? it run's solid idle at 1100 rpm when hot.
Because the problem has been there from the start, I strongly suspect the timing is retarded.

At the high idle RPM you have, a smaller vacuum leak would not be very noticeable but could cause a lean condition. Check that all vacuum ports on the intake, intake manifold and carb are connected and/or blocked. Check the vacuum line from the intake manifold to the trans modulator valve is connected.

Is that idle RPM in PARK? What does the idle go to when in DRIVE? (foot on the brake).

What is the timing in DRIVE at idle? (Parking brake engaged, wheels blocked and foot on the brake when checking the timing at idle in gear)
 
#11 ·
In addition to the above info, I'd suggest that that 14" electric fan may not be up to the airflow requirements of that 396. You don't necessarily need a huge radiator for a big motor if you have enough airflow. In fact, a heater core is big enough to cool some motors, with enough nice cool air flowing through it. One of the keys is making sure all available airflow goes through the core, not around it, and that there is a place for the air to go once it makes it through the core. :cool:
 
#12 ·
454C10 said:
there is a difference in head gaskets with the early 396's. the wrong gasket will block a water port and make it run hot.
Which 396's were they?

If a head gasket from a Gen 5 or 6 is used on a Mk IV, there can be overheating issues. The gaskets look similar and will bolt up (unlike Gen 7 gaskets), but are different as to how the water's transferred at the rear of the block into the heads.

The later blocks have passages (as do the later gaskets) that allows coolant to flow up from the block into the heads between the cylinders, as well as from the back of the block. But there's just one smaller passage at the back, instead of the necessary (on a Mk IV) two larger passages.

Earlier blocks can be drilled for the later coolant flow path, but as cast and machined, they lack the necessary passages.
 
#13 · (Edited)
Frisco said:
Because the problem has been there from the start, I strongly suspect the timing is retarded.

At the high idle RPM you have, a smaller vacuum leak would not be very noticeable but could cause a lean condition. Check that all vacuum ports on the intake, intake manifold and carb are connected and/or blocked. Check the vacuum line from the intake manifold to the trans modulator valve is connected.

Is that idle RPM in PARK? What does the idle go to when in DRIVE? (foot on the brake).

What is the timing in DRIVE at idle? (Parking brake engaged, wheels blocked and foot on the brake when checking the timing at idle in gear)
Hello sir. The engine was in a Nova before i put it in the Jeep, it had the same distributor and timing, and it didn't had those kind of problems.
The Rpm at idle is in park, not sure what the rpm is in idle, gear, but it drops plenty, maybe to 700-800 rpm, the ignition timing is locked so it's always at 37°
I''m suspecting that there is air on the system, what is the best way to get rid of the air from the system, IF that's the problem ???

What's the best way to flush the radiator, maybe the whole cooling system ?

P.s. I have one 14" fan and other that is 10"

Best regards.
 
#14 ·
There' no air in the system, it does heat just as fast when driving on aprox 40 mp/h, the ign. timing is locked at 37° the carb was on this engine when it ran fine in the Nova, the water pump pump's the water.
I have no clue what is wrong with the engine :(
 
#16 · (Edited)
The electric fan's are new, there was a 500 hp sbc 406 in this Jeep and it was used plenty... and with the radiator, shouldn't it run cooler at speed, even with "small" radiator. It has capacity of 9 liters of fluid and is 3 row unit.
Also i don't think i have room for mechanical fan :( otherwise i would run it.
 
#19 · (Edited)
monzter said:
There' no air in the system, it does heat just as fast when driving on aprox 40 mp/h, the ign. timing is locked at 37? the carb was on this engine when it ran fine in the Nova, the water pump pump's the water.
I have no clue what is wrong with the engine :(
Assuming that the engine is exactly as it was when in the Nova with no changes done to the timing or carb or the vacuum lines, or thermostat, the only thing left to consider is the radiator and the air flow thru it. With everything else being the same as when in the Nova, my conclusion is that the cooling system is not up to what you require.

A larger capacity (or possibly an aluminum) radiator, good shrouding to direct the air flow thru the cooling fins, ample fan (electric or rigid mounted), and possibly raising the hood by 1/4"-1/2" closest to the windshield to allow a better flow of air from the engine compartment should correct the overheating.

Just out of curiosity, is the location of the temp sending unit still the same as it was when in the Nova? Is the temp gauge matched to the sending unit? If not, this could be giving you false temp readings.

NOTE:

An operating temp of 195 degrees is very normal and an expected temp for that engine. Running at 230 degrees and above is overheating and should be corrected.
 
#20 · (Edited)
The 14" fan is a Mr. Gasket unit, the other 10" is from Japan :rolleyes: but it's very powerful.

The changes i've made to the engine are very little, i changed water pumps, took the summit electric unit of and put moroso aluminium hi-flow pump on, the thermostat is the same. i took the distributor out but timed it in at the same 37° There are a few vacuum port's on the carb and they are all in usage.
The sending unit is in the water neck and it was there on the 350 engine i had in the jeep, the sending unit is new, the gauge is auto meter ultra lite electric gauge.
Maybe i'l just move the radiator a bit further, what kind of mechanical fan do you recommend if i do that, it can not be long, maybe 2" at the most,,, BUT i can't say for now. also i have a shroud to use with the mechanical fan.

Best regards.
 
#21 ·
If you lay a Taurus 2 speed fan on it's face and feed 12v to the high side, it will float like a hovercraft. That's a pretty crude test, but it's a fairly heavy fan unit, so it's obviously moving a lot of air to be able to lift it's own weight. They supposedly move somewhere between 3000 and 4500 CFM. Maybe see if either of your current fans can do that?? That's the closest thing to a CFM test I can think of outside a lab, but it's a little more scientific than assuming a given brand name and/or model is up to the task. :cool:
 
Status
Not open for further replies.
You have insufficient privileges to reply here.
Top