454 overheating

I've got a 454 that overheats while driving. Idling in heavy traffic on a 100 degree day is no problem, it runs at whatever the thermostat is. But get on the road and it will boil within 20 miles, no matter what temperature it is outside. It's a gen 5 454, I believe a 1993, in a 1971 chevy K20. Currently has a brand new heavy duty 4 core radiator, dual electric fans, highflow iron waterpump and a 160 degree thermostat. When I got the pickup it had a 3 row questionable radiator, a stock pump, a stock flexfan and a 195 thermostat. All these changes didn't help it a bit. I had thought that maybe the waterpump was a reverse rotation, spinning backwards (it has v-belts), the new highflow pump didn't help. Thermostats only change it's idling temp. It has stock '93 heads with what I call peanut ports (small) and a 60's era cast iron highrise GM 4bbl intake. The ports don't really match up. I don't know why this would affect heating though. It had a stock lowrise 4bbl manifold when I bought it. I have switched distributors, and had timing at every imaginable degree. No change. It had a 4150 Holley, now a 750 Edelbrock, no change. I have rejetted many times. I have double checked temps with other gauges and my infared thermometer. It runs great, good power. This engine has only 3500 miles on a complete rebuild. I found out that this engine was formerly in a 1947 chevy coe carhauler. It overheated for that guy too. He even plumbed 2 radiators to it. It was yanked out and replaced. A guy bought this engine, had it completely rebuilt and installed it in this K20, then I bought it. I'm out of suggestions. Any help would be appreciated.

I've got a 454 that overheats while driving. Idling in heavy traffic on a 100 degree day is no problem, it runs at whatever the thermostat is. But get on the road and it will boil within 20 miles, no matter what temperature it is outside. It's a gen 5 454, I believe a 1993, in a 1971 chevy K20. Currently has a brand new heavy duty 4 core radiator, dual electric fans, highflow iron waterpump and a 160 degree thermostat. When I got the pickup it had a 3 row questionable radiator, a stock pump, a stock flexfan and a 195 thermostat. All these changes didn't help it a bit. I had thought that maybe the waterpump was a reverse rotation, spinning backwards (it has v-belts), the new highflow pump didn't help. Thermostats only change it's idling temp. It has stock '93 heads with what I call peanut ports (small) and a 60's era cast iron highrise GM 4bbl intake. The ports don't really match up. I don't know why this would affect heating though. It had a stock lowrise 4bbl manifold when I bought it. I have switched distributors, and had timing at every imaginable degree. No change. It had a 4150 Holley, now a 750 Edelbrock, no change. I have rejetted many times. I have double checked temps with other gauges and my infared thermometer. It runs great, good power. This engine has only 3500 miles on a complete rebuild. I found out that this engine was formerly in a 1947 chevy coe carhauler. It overheated for that guy too. He even plumbed 2 radiators to it. It was yanked out and replaced. A guy bought this engine, had it completely rebuilt and installed it in this K20, then I bought it. I'm out of suggestions. Any help would be appreciated.

You may want to check base time.
Does the heater quit working the same time it heats up ?
But if all else fails run or have a repair shop run a chemical /block/head gasket check on it.
http://tools.batauto.com/index.php?crn=223&rn=1086&action=show_detail

What brand (Flex-a-Lite?) of fans did you install and do they completely cover the radiator? Are the fans mounted in a shroud, or do you have 2 individual fans. Low c.f.m. or leaving parts of the radiator unexposed would cause high speed/high r.p.m. overheating. I have a 400 in my Biscayne and at one time it had the same basic symptoms. The faster I would push it, the hotter it would get. If I slowed down, it would run cooler. When I swapped in the V-8, I installed a bigger radiator and dual fans, it wasn't quite enough. I solved the problem by adding another dual fan unit. 4 fans total is what it needed.
One of my customers swapped to an electric fan on his hot rod and it had the exact same symptoms, but he wired the fan backwards. It was pushing air out the front, so it was fine while driving slow. I wouldn't assume that you would make the same mistake, just need to double check a few things.
I diagnosed a Jeep that had a wench mounted on top of the bumper. The wench deflected the air away from the grille at highway speeds. You don't have anything in front of the grill by any chance, do you? Any extra coolers in front of the condensor core?
Can you verify that you actually have good coolant flow through the radiator. You might drain out 1/2 gallon or so of coolant, disable the fans, and let it run until you are sure that the thermostat should be open (170*+). Carefully look down into the radiator to see if coolant is flowing through.

Have you tried driving it w/o the thermostat to see what it does? I have seen problems with cheap thermostats that were way out of calibration. Standt has a line of t'stats called Superstat, so you might consider one if you remove what's in it now. I always drill an 1/8" hole in thermostats (in the disc portion) to easily purge the air from the system. Then you don't have to wait for the 'stat to open before all the air is released.

If you haven't lost any coolant then the engine should be fine. If there were major gasket/head problems then there would be a loss of coolant. There's onlt 2 places it would come out, either in the oil or out the tail pipe.

I'd check the thermostat closely and 2nd, make sure there's enough air going through the radiator.
If you don't do any offraoding, you might check into adding an air dam. Some of the early '80s Chevys came with them, so look for one if you're ever junk yard hunting.

Speaking of the distributor. Make sure the vacuum advance is working. Like MT said too, you might want to shoot the timing, just to make sure it's ok.

Good luck.

Thanks for your responses. I talked with the guy at NAPA who rebuilt the engine, a pretty reputable guy. It was hot tanked, magnafluxed, etc. I don't know how base timing could be off 2 times. To my knowlege, it was pulled from a wrecked 3500 Chev and installed in the COE carhauler, and overheated from day one. It does have a superstat in it now, and has had 3 different temps installed, 160,180 and 195. Fan setup was from Vintage Air I believe, and is specificaly designed for 67 to 72 Chevys. It had a stock shroud and a good flexfan before, the problem hasn't changed with any modifications at all. No, it doesn't have a winch or air restriction. I haven't tried no thermostat yet, but on 454 irrigation powerunits, this is a no no, and I have had several farmers burn them up by removing the thermostats trying to solve a heating problem. But, this may help my problem. I will try it.Thanks
again!

I recommended the use w/o the t'stat just for diagnosis. I agree also that bad things can happen, thermostats are mandatory. Irrigation water caused an undercooling affect which caused bad results. In your case, air-to-water would be more forgiving.
You're sure about the water pump? You have the one for early '80s and not the late 80s/early 90s? It's strange w/your problem, you seem to know what you're doing, just something isn't right. I would pull the thermostat and check the flow of coolant through the radiator.

What carb/jets do you have? Have you pulled a spark plug to check the color of the porcelain? The color should be tan, if it's white and speckeled it would be way lean.

Do your radiator hoses have springs on the inside. I have seen hoses collapse when the thermostat opens. Have you cleaned the air conditioning condenser I have seen them covered with bugs and mud.

Everyone tells me on a daily basis that I am in Left Field,so here is a left field idea.Is it at all possible that both the trucks that this engine was in the rad was flowing the wrong way?Seems possible to me.

Did you every try flushing it as some old gasket or something is restricting flow?

Hey have you made sure that you don't have any air bubbles. I had that problem in my '70 chevy but also, what they are talking about the 4 fans i think or the shroud isn't directing airflow through your radiator right.

Did you every try flushing it as some old gasket or something is restricting flow?

I agree. It sounds like a restriction somewhere. I'd flush it to see how much water you can move through it.

I've ran big blocks in Impalas and Novas, never ever had a overheating problem and it seems that you've done everything possible to fix it.

I go with having the coolant checked for combustion gases, I like the collapsed radiator hose suggestion too. The mechanical obstruction idea is a possibility, but it would have to be something done deliberately or a big chunk of gasket, rtv, maybe an old freeze plug jammed up into a cooling passage.

It might be a bit of work, if the above suggestions don't pan out, look at the freeze plugs on the side of the block, if they appear to have been changed there still might be an old behind one or more of them. Once you get them out, poke around the passages with a piece of coat hanger.

Bob

The gen v motors are reverse cooling. This means you need a reverse flow water pump. I keept the factory serpentine set up on mine w/a edelbrock reverse flow aluminum water pump and a aftermarket aluminum radiator & electric fan!

The gen v motors are reverse cooling. This means you need a reverse flow water pump. I keept the factory serpentine set up on mine w/a edelbrock reverse flow aluminum water pump and a aftermarket aluminum radiator & electric fan!

Welcome to AF, good info, but look at the dates before posting this is way too old and dead to continue, thanks.