71 454 Radiator overflow

[Mike Sealy]

Every time I cap off my radiator, the overflow dumps about a gallon out after driving the car. I have been told the big blocks tend to run a little hot, mine in traffic will get up to the 240 range then drops to 200 as long as I am running no greater than 60. Water pump is new high volume unit, radiator is original but recored, engine has about 2000 miles on complete rebuild. Stat is 180 degrees. Any suggestions or comments?

[Mike Sealy]

Re: 71 454 Radiator overflow

To answer the questions all ready received.

1. The car has AC. 2. I have used a 50/50 mix with a redline additive. 3. Car is running 250 at idle in traffic and low speed stop and go. 4. High flow water pump has been used. 5. Engine was rebuilt by reputable rebuilder, Square D Racing, Mooresville,NC. 6. Compression on rebuild is 9:1 7. Radiator is recored, all seals are in place as well as shrouds. 8. Engine performs great until it gets to the 250 degrees then is a little sluggish. 9. How could an engine perform well with a small gasket leak? Not overly excited about pulling the heads. 10. Fan clutch is thermal unit, Eaton replacement for this year car. 11. Have not tried anyother fan clutches but have heard thre is a replacement unit from GM that will keep fan engaged longer and is noisy. 12. Fan blade is replacement unit from GM. 71 454 had a unique fan blade with small fingers on the end but overall identical.

Any suggestions or resources you know in the Charlotte,NC area?

[Mike Sealy]

Re: 71 454 Radiator overflow

To answer the questions all ready received.

1. The car has AC. 2. I have used a 50/50 mix with a redline additive. 3. Car is running 250 at idle in traffic and low speed stop and go. 4. High flow water pump has been used. 5. Engine was rebuilt by reputable rebuilder, Square D Racing, Mooresville,NC. 6. Compression on rebuild is 9:1 7. Radiator is recored, all seals are in place as well as shrouds. 8. Engine performs great until it gets to the 250 degrees then is a little sluggish. 9. How could an engine perform well with a small gasket leak? Not overly excited about pulling the heads. 10. Fan clutch is thermal unit, Eaton replacement for this year car. 11. Have not tried anyother fan clutches but have heard thre is a replacement unit from GM that will keep fan engaged longer and is noisy. 12. Fan blade is replacement unit from GM. 71 454 had a unique fan blade with small fingers on the end but overall identical.

Any suggestions or resources you know in the Charlotte,NC area?

[Patrick H.]

Re: 71 454 Radiator overflow

Mike,

One thought is that my 350/270 AC car, with the same type radiator as your 454, used to overflow upon stopping after a long run, until I replaced the radiator cap with another, even though the first one was new (actually a reproduction unit). Ever since, no problem with overflow.

Just a thought.

Patrick

[Patrick H.]

Re: 71 454 Radiator overflow

Mike,

One thought is that my 350/270 AC car, with the same type radiator as your 454, used to overflow upon stopping after a long run, until I replaced the radiator cap with another, even though the first one was new (actually a reproduction unit). Ever since, no problem with overflow.

Just a thought.

Patrick

[Nick Liarakos]

Re: 71 454 Radiator overflow

Mike, In my personal experience with my 71 LS5, the car hasn't had a tendency to run significantly hotter than any small blocks I've had. With a 180 thermo and a copper/brass repl. radiator, my car never reaches 210 even in traffic or at high speed. Everything is stock, and my fan shroud seals are not in very good condition, either. The temp sender is original.

First off, is the engine really running hot or is the gauge reading inaccurately due to a replacement sender? There has been a lot of discussion about the inaccuracy of replacement senders on this board, so take a look in the archives for more. Also, my friend recently encountered a problem while building a 454 for his 71 Chevelle that may be related. The Felpro head gaskets that he received were missing a few of the holes necessary for coolant flow to the heads. It took him a lot of effort to find correct gaskets. The heads he used are early closed chamber (pre '71) units, so I'm not sure if these same passages are used on our heads, but it may be worth looking into if all else fails. If you would like more info on this, e-mail me privately and I will get the specifics from my friend.

Other than the usual items (rad., pump, shroud, thermo, timing, etc.) that you've probably already checked, I can't think of anything else. Good luck and happy wrenching.

Regards, Nick 71 LS5

[Nick Liarakos]

Re: 71 454 Radiator overflow

Mike, In my personal experience with my 71 LS5, the car hasn't had a tendency to run significantly hotter than any small blocks I've had. With a 180 thermo and a copper/brass repl. radiator, my car never reaches 210 even in traffic or at high speed. Everything is stock, and my fan shroud seals are not in very good condition, either. The temp sender is original.

First off, is the engine really running hot or is the gauge reading inaccurately due to a replacement sender? There has been a lot of discussion about the inaccuracy of replacement senders on this board, so take a look in the archives for more. Also, my friend recently encountered a problem while building a 454 for his 71 Chevelle that may be related. The Felpro head gaskets that he received were missing a few of the holes necessary for coolant flow to the heads. It took him a lot of effort to find correct gaskets. The heads he used are early closed chamber (pre '71) units, so I'm not sure if these same passages are used on our heads, but it may be worth looking into if all else fails. If you would like more info on this, e-mail me privately and I will get the specifics from my friend.

Other than the usual items (rad., pump, shroud, thermo, timing, etc.) that you've probably already checked, I can't think of anything else. Good luck and happy wrenching.

Regards, Nick 71 LS5

[Jack H.]

Re: 71 454 Radiator overflow

(1) If you're filling the system FULL each time, it WILL puke coolant

to achieve steady state internal expansion volume.... (2) Purging the 'one gallon' amount you state IS excessive and indicates

a genuine cooling problem unless there's a bit of exaggeration in

the volumetrics of your initial statement. (3) Knowing what the actual coolant temp is vs. what the gauge reads

helps sort wheat from chaff and this can be done by methods outlined

in the archieves (thermometer on outlet hose). (4) Saying you see hot temps at idle vs. lower temps while in motion

and/or at higher engine RPM again points to a real coolant system

issue. Tends to indict the fan/fan clutch/shroud and air focus

system (this includes the modest black plastic 'spook' lip bolted

to the lower front nose that was intended to disturb under-car

air flow and divert some into radiator via intentional turbulence). (5) Flakey/leaky rad cap and/or loose/incorrect mount of hose clamps

(rad inlet/outlet and heater hoses) can allow system not to seal

and boost temp (both steady state as well as transient) by lowering

system pressure.

[Jack H.]

Re: 71 454 Radiator overflow

(1) If you're filling the system FULL each time, it WILL puke coolant

to achieve steady state internal expansion volume.... (2) Purging the 'one gallon' amount you state IS excessive and indicates

a genuine cooling problem unless there's a bit of exaggeration in

the volumetrics of your initial statement. (3) Knowing what the actual coolant temp is vs. what the gauge reads

helps sort wheat from chaff and this can be done by methods outlined

in the archieves (thermometer on outlet hose). (4) Saying you see hot temps at idle vs. lower temps while in motion

and/or at higher engine RPM again points to a real coolant system

issue. Tends to indict the fan/fan clutch/shroud and air focus

system (this includes the modest black plastic 'spook' lip bolted

to the lower front nose that was intended to disturb under-car

air flow and divert some into radiator via intentional turbulence). (5) Flakey/leaky rad cap and/or loose/incorrect mount of hose clamps

(rad inlet/outlet and heater hoses) can allow system not to seal

and boost temp (both steady state as well as transient) by lowering

system pressure.

[Tom Fetchik]

Re: 71 454 Radiator overflow

I have a 71 454 LS5 and it runs cool without any overflow. There could be several problems. A inoperative fan clutch will cause overheating as will restricted (dirty) water jackets in the block. You really have to go through these things step by step. When all is clean and working BB run just fine.

[Tom Fetchik]

Re: 71 454 Radiator overflow

I have a 71 454 LS5 and it runs cool without any overflow. There could be several problems. A inoperative fan clutch will cause overheating as will restricted (dirty) water jackets in the block. You really have to go through these things step by step. When all is clean and working BB run just fine.