A friend is having issues with a 454 big block that is overheating after shutting off.

I remember this used to be referred to as percolating, where the water overheats sitting in the engine once the pump and fan stops, and then blows out of the radiator or overflow tank.

The problem is it has been so long since I have been around any like this, I can't think of what the common problems were then.

His engine is running about 200 all the time, although if sitting in traffic, it creeps up to 210-220. He was thinking the fan clutch was bad in that hot it wasn't pulling air through, and he replaced it, but that didn't change anything.

He has tried flushing the coolant out in case there was old junk in there but no change either.

I'm thinking maybe the radiator needs to be pulled and cleaned out, although it looks good looking down the opening, not the crud on the tubes like you usually see in bad one.

Fan shrouds, seals, spoilers, etc are all in place and the setup is all stock, nothing changed, bubba-ized, hot rodded, or anything.

Any ideas? He is wondering about the water pump, but my experience with water pumps is that they work or they leak and I haven't had any other experience. Maybe just lucky, but that is what I have experienced.

So, idea where we should go?

 

He's probably overfilling the system and the car is puking the excess on the ground.

What year is the car? If it's earlier than '73 it does NOT have an overflow tank!

 

It isn't the overfilled part, it is just plain getting hot. You can see it on the gauges. And yes, they are the old original senders, not the replacement senders that are off.

If you shut it off and then check the gauges, the temp has climbed to 230 and higher. You can walk past and here the coolant boiling and kicking into the overflow. And if you try starting 5 minutes after, it is just barely turning over.

Let it sit 20 minutes or more, and then it works ok.

 

Change the thermostat to a 160 degree unit and see how the engine temperature reacts. If the temp drops to around 180, run it there...it shouldn't be a problem. If it still stabilizes at a high temperature, do a radiator "cleaning" -- not a radiator flush. You can find radiator cleaner at the auto store in the same area as radiator flush products. Flush just gets the loose gunk out of the system; cleaner removes the built-up scale in the radiator fins [which greatly reduce the radiator's efficiency]. Follow the directions closely. I believe that should solve your problem (along with the cooler thermostat).

 

VERY common misconception.

Putting a lower temp thermostat does NOTHING to lower the temperature of an overheating system. Period.

The correct amount of AIR passing through a properly functioning (i.e. clean and unobstructed) radiator is the ONLY way to COOL things DOWN.

 

Not true at all........
Pre 73 cars had expansion tanks, Big blocks had em, the 327 had one in 68

 

The head temps in my 454 jump up to *280 after shut down--hot engine with no coolant circulating- thats totally normal. Mine use to overflow coolant after shutdown and I found it was because there was still air in the cooling system. Once I got all the air out it has never overflowed again.

Greg

 

How do you get the air out?

 

We found last week a leak around the thermostat housing so we pulled it, put a new gasket on, and I had him put in a new 180 degree thermostat instead of the 195. Not that would cool it, but at least it wouldn't be pushed to a higher amount than necessary and in case the old one was not opening all the way.

I thought the leak might be letting off pressure. I took his housing and sanded it flat, as it was warped like most.

That didn't fix anything unfortunately. Still running about 200 in normal driving, climbing to 210 if sitting. Runs up over 230 after shutting off and higher.

Usually with an overflow tank, you can get all the air out as when it cools, it sucks coolant back into the empty air spaces. But it hasn't so far solved the issue.

 

I'll have him pick up the cleaner. Wait, I'll pick it up to be sure we get the right stuff and help him try that this weekend.

It doesn't look scaly looking down the fill opening, but it is always possible.

 

http://www.sjdiscounttools.com/uv550000.html

Works awsome.

Greg

 

I had the same symptoms you describe on my '71 454. Turned out to be plugged cores in the radiator.[Radiator shop R&R'd core] Engine runs @ 180 on the hottest day on the highway [180 thermo] Maybe 205 idling in traffic same days. No longer puking coolant on the garage floor after drive on hot days.

 

Mark.... Since you installed a 180 stat and found no temp drop, there's no need to try the 160. Since the stabilized operating temp is well above 180, there is some problem with the system. If it has been a while since the cooling system was cleaned, I really would give that a try. It will be a bit of trouble, but fairly inexpensive [compared to replacement parts]...and it can be quite effective. If that doesn't help, it could be thermostatic fan or water pump problems. {Check the fan by getting the engine up to temp, popping the hood, and turning off the ignition. A "good" fan should stop turning after just a couple of rotations. If it keeps spinning, the fan is malfunctioning.}

 

Hi,
I've had my BB 454 for 14 years and had overheating probs at fast motorway speeds for years and never sorted them out till last year, around town it would sit at 190-200 all day, but go at constant speeds above 65 mph and the temp would creep up to the point where it boiled over if i didn't drop my speed. after flushing the system many times, new w/pump, recored rad, new hoses, caps, and different fans, I finally found out what the problem was after being forced into changing my cyl heads due to a bolt shearing off when fitting new headers. There was a piece of limescale blocking off the waterway at the rear of the block on one side if the engine. Possibly if i'd of had access to a infared temp sensor i might have found it earlier.
But one thing i will say you could try leaving the flushing compound in the system a lot longer than they state on the box, i.e. a couple of days as you might have a stubborn piece of scale in the system that takes some time to break down.
Good luck i hope it doesn't take you 12 years to sort out like me.
Regards Peter

 

Does the distributor have a vacuum advance and is it connected to full manifold port? 200* is not really running hot .

 

Is the coolant foamy when idling?
Could be a head gasket.
Or could be the rad needs to be cored. (Tanks taken off and the cores wired out)
Bad water pump.

 

Expansion tanks are very different from overflow tanks. Please go do a search of the archives to learn the differences.

Again, pre-73 Corvettes did not have overflow tanks.

 

there not that different, cap location (pressurized or not) and draw is all

 

Quote:
Originally Posted by Mike Ward
Expansion tanks are very different from overflow tanks. Please go do a search of the archives to learn the differences.

Again, pre-73 Corvettes did not have overflow tanks.


They are completely different. Expansion tanks are pressurized and DO NOT reclaim expelled fluid. Overflow tanks DO reclaim fluid and effectively remove any air trapped in the system.

I added an overflow tank to my '69 which also has an expansion tank.

 

exactly.