The Stovebolt Site Forums The Shop Area Engine Shop Rebuilt 1948 Chevy 1/2 ton 216 C.I. overheats

Hello Advance Design Chevy Truck Fans. I have a 48 Chevy 1/2 ton 216 C.I straight six which is numbers matching and appears to be the original stovebolt enginge. I need help as my engine has an over heating problem that I have been troubleshooting and I have not found and/or fixed the problem. Let me tell you what I know.
Within 30 minutes of idling she pegs out the temp gauge "212 'F" It takes longer if I'm driving, but she creeps up to +200'F and then when you shut the engine off of course the fan stops spinning and the temp gauge pegs out! I had my engine rebuilt several years ago and we installed a new aftermarket water pump. Still I just installed another rebuilt water pump in an attempt to fix the overheating problem..Doing research I was instructed to make sure that the back of the water pump impeller and the water pump backing plate it is critical that the gap in no more that 0.040". They claim that several aftermarket water pumps have too large of a gap and they don't push coolant like they should. I ensured that I had a gap no larger than 0.040" and the coolant appears to be strongly swirling when watching it with the radiator cap off as soon as the thermostat opens. It has the original style OEM radiator and it appears to be working as advertised. I've researched and played with the timing. The vacuum advance on the distributor seems to be working fine while accelerating the engine. All the plugs have a nice tan color so it doesn't appear to be a fuel mixture problem. I replaced the thermostat with a 160'F thermostat. My radiator cap is the non pressurized type. I've watched the temperatures with a infared thermometer. The temp gauge is not wrong as I have measured the temperature where the capillary tube screws into the cylinder head. I've used the infared thermometer to check the top and tanks of the radiator and radiator tubes, There's no bubbling of the coolant. There appears to be no oil in the coolant and/or coolant in the engine oil. There's no white smoke coming from the tail pipe and no sweet smell of antifreeze. I have also installed a 6 volt pushing electric fan in front of the radiator to help out the situation but it only minimally helps out. I've thought about fabricated a radiator shroud, but this may not even be worth doing as far as I know these old truck didn't come with a radiator shroud and doing so maybe putting a band aid on the situation. I appreciate any advice.

The fact that it's heating up so fast at startup leads me to suspect that exhaust gas is entering the cooling system through the head gasket.

Buy one of those test kits that use blue fluid in a tube that sits on the radiator filler neck while running the engine. If the fluid changes from blue to yellow, you have exhaust gases in your cooling system.

I appreciate the advice. Thanks

I should point out that these engines do not have a history of overheating. They will run at 180 degrees all day long and only creep higher under heavy load. When everything is operating correctly, you do not need an electric cooling fan or fan shroud, even in the middle of a 90+ degree summer day.

Good to know. I have exhausted pretty much everything that I could troubleshoot and/or check. I'll let you know what I find out once I do the coolant test that you recommend. I hope I don't have a blown head gasket and/or cracked block!

Try opening the coolant drain on the side of the block to see if coolant does come out .It may be plugged in that area which is fairly common .The big trucks did come as a option with a fan shroud so you may be able to find one but don’t know if they fit the pickups but don’t see why not.

Stovebolt engines have a nasty habit of building up a thick layer of crud in the bottom of the water jacket that shortens the area where coolant can contact the cylinder walls. Short of removing the head and manually dislodging the sediment with a long probe, it's difficult to get rid of it. I've had some degree of success by running a pretty strong solution of muriatic acid (technical grade hydrochloric) and water in the cooling system followed by a strong dose of baking soda to neutralize the acid. About 2 cups of the acid that's sold in the big box hardware stores for masonry cleanup to a cooling system full of water- - - - -run the engine for 30 minutes- - - -then add a whole box of baking soda to a fill with clear water and run for 10 minutes as a neutralizer. Then flush with clear water and refill with a 50/50 mix of antifreeze and water. The only downside is the possibility of opening up thin spots in the freeze plugs and creating a leak.
Jerry

HeavyChevy48 said his engine has been rebuilt so I wouldn't expect a buildup of crud in just a few years.

That's no guarantee that they got all the crud out of the water jacket.

What is the water temp coming out of the thermostat verse what's coming out of the bottom of the radiator?

I've read elsewhere here that some of these engines can get essentially a big air bubble towards the rear of the cylinder head that makes it overheat, but you can burp it by unthreading the temp sensor til green stuff comes out? Engine cold, of course.

Last time I checked the thermostat temperature is around 180 degrees and the radiator outlet is about 150 - 160 degrees. Where the temp gauge sensor screws into the head it's unfortunately around 210 degrees at idle.

I've checked my radiator coolant for a possible combustion leak and there was no color change or indication of a combustion leak which is good, but I'm still chasing an overheating engine. My engine was totally rebuilt just a few years ago by a professional and by a trusted machine shop. I've replaced by water pump and I've checked the engine timing. I've check the heat riser and/or valve that is temperature controlled to add heat to the intake manifold during start up to make sure it's not stuck. The engine runs great, but it still overheats? I'm going down the path of purchasing an aluminum radiator but what I'm finding is no one makes one with the stock inlet 1.25" and stock outlet 1.50" radiator connections. Finding adapter for 1.50 to 1.25 and 1.75 to 1.50 is like trying to find a unicorn! LOL! I appreciate all the suggestions you guys have been providing.

If your radiator doesn't leak, a radiator shop (assuming one still exists in your area) could clean it up for you. Years ago, I had a radiator that I was having trouble with and took it to a shop to have it "rodded out". They removed the top and ran rods down thru the tubes to clean the crud out of them. It may be possible to get yours clean by filling it with a mild acid solution and letting that sit for a few days.Lay it on it's face and fill it with the solution (not while installed on the engine.) Use something like this:

[on edit] I went back and read your first post. You say it's getting to 212F, but is it boiling over? A 50/50 mix of coolant raises the boiling temperature significantly, so if you're not loosing coolant, your engine isn't "overheating." Changing to a lower temperature thermostat doesn't help, but just opens completely at a lower temperature, which is not necessarily good. If the radiator is doing it's job, it should keep the engine at roughly the thermostat temperature.

Have your original radiator boiled out / repaired.

Flush your system. I'll guarantee the bottom rear driver side corner of the block is sludged up. Remove the petcock fitting and poke around in there. Use high pressure water, etc.

Are you using a zero pressure radiator cap?

I use a 4psi cap and a 160T stat. The truck pretty much stays at 180 on the highway and at idle.

I've used the blue solution and it doesn't always work, you could tie a rubber glove on the filler neck and let it run until it get's to 212* and see if the glove expands. If it does you have a head gasket leak.

Thanks for the info. The design of my original 48 Chevy 216 C.I. engine uses a non pressurized radiator cap. And yes when the temperature climbs towards 200 degrees plus I am losing coolant. I actually placed an overflow plastic reservoir on the firewall and it collects the coolant and when the radiator cools down the coolant returns to the radiator so I don't lose it anymore. I learned that trick from an owner of a 47 Chevy Panel Truck. My engine is still overheating. My radiator is an aftermarket OEM stock style radiator that is new, but it doesn't mean that it has maximum coolant flow through the core. I will tell you that the outlet temperature of my radiator is at least 20 degrees cooler than the inlet temperature.

My engine was totally rebuilt. I would hope that the engine block was dipped and/or cleaned before it was machined. Just because I could I ran two bottles of Prestone Heavy Duty Cleaner for at least a week just to make sure my engine and radiator were clean. I got a little bit of dirty water out of my engine when flushing it. I bought a new aftermarket OEM/Stock Radiator because my original radiator leaked. I will tell you that the outlet temperature coming from the radiator is at least 20 degrees cooler than the Inlet temperature. I am running a stock non pressurized radiator cap,

Last time I checked the thermostat temperature is around 180 degrees and the radiator outlet is about 150 - 160 degrees. Where the temp gauge sensor screws into the head it's unfortunately around 210 degrees at idle.

That area is normally the hottest place on the engine. If you aren't boiling over, you're probably ok. I think flushing the entire system as previously mentioned - pull the water pump and core plugs to get better access if necessary - will cool it off a little in that area.

The 20 degree difference in temperature between the top hose and bottom hose indicates your radiator is functioning properly. No need to buy a new one.

First off, how many miles are on the engine since rebuilt? A rebuilt engine will run hot till it has enough miles on it to smooth out the cylinders, its not surprising a new engine is hot.

Is the coolant boiling out on the ground?

What type of break-in procedure was performed on the engine? Did it get hot?

Where on the engine is the temp sender screwed in to? I have a 250, not sure where on the 235 it goes.
A temp sender screwed into the head between cylinders will read hotter than at the thermostat just because it's so close to the combustion chamber, and it will continue to heat up once the engine is off.

The temps you need to worry about is what is coming out of the thermostat housing, and what is going back into the engine.

You can purchase thermocouples off Amazon for cheap,( Thermocouple Thermometer Digital K Type Thermometer with 4 Thermocouples,
-328~2500℉ Measuring Range HVAC Dual Channels Temperature Meter Gauge with LED Backlight & ADJ Compensation $28 ) and check the temps while driving.

The getting hot after shut down is nothing to worry about, they all do it.

My 250 would heat up over 220 before dropping back down, did it every time I drove the truck. Once up to temp it stayed right at 200 and then would climb when I shut it off. I cured it by moving the temp probe from the head ( between cylinder 1 and 2 ) to the bottom of the thermostat housing. At the thermostat housing it reads the average water temp of the whole engine. It now runs 180 degrees all the time and still climbs once shut down.

Joe,

How are the thermocouples you used attached to the engine? Did you attach them temporarily, or are they installed as to be permanent?

The one I have I use for A/C work, it has a steel probe that just needs to touch the tubes on a A/C system. I use foam insulation wrapped around the probe so it isn't effected by outside air.

For your truck, I bet you could wire tie them around hoses or tape them. My older gauge I had I used on my uncles Stanley Steamer to measure steam temp going into the engine, I had to use wire to tie the probe to the steam line, but all it had to do was touch the pipe to get a good reading.

The cheap infra-red no touch thermo guns work really good for checking temps also. I think you could cut some hose and split it down the middle and use it along with wire ties to seal the thermocouple end to the hose you want to measure. Some of the cooling fan controllers insert the thermocouple under the radiator hose between the outlet / inlet and the hose, I haven't seen one personally, but they may be a thinner wire type and not the probe type.

On my truck, I drilled a hole in the thermostat housing that wasn't being used, it was cast for hole but never drilled and tapped. After looking at the 250's head, I could see just how close to the chamber the probe was so it was no surprise it read hot.

Thanks, Joe!

How much coolant do you have to add to the radiator on a regular basis? If the coolant isn't boiling, the engine isn't overheating- - - - -the gauge is lying to you.
Jerry

Sorry I didn't get back with the Stovebolt Community sooner. I'm getting ready to continue troubleshooting my 216 overheating problem again. Where I last left off is I tried some Evapo-Rust Thermocure Cooling System Cleaner. It turned the water a dark blackish brown. I flushed it all out until the water was clean and it still overheats with fresh antifreeze. I'm looking at using a stronger flush, Fleetguard Restore Plus as it's a mild acid based cleaner. I have not back flushed my system yet. Can anyone verify that a 48 216 engine does not have a coolant distribution tube? CoPilot also known as Artificial Intelligence claims that my engine has a metal coolant distribution tube that are prone to rust out and this can cause cylinders 5 and 6 to overheat. I can find no where on the web and/or my repair manual that a 216 has such a coolant distribution tube.

No internal coolant distribution tube on 216.

First off, how many miles have you driven the truck since it was rebuilt? new engines always run how till the cylinders wear in,

How much coolant is in the radiator? to the top or just above the core? How much hits the ground? Is it a continuous flow?

30 minutes of idle is really hard on a fresh engine, so quit doing that! this is not a good indicator of how the cooling system is working on a fresh motor,

When driving, if the coolant temps keep rising, this is normally a sign of a weak radiator or lack of air flow into the radiator, a slow rise is telling you the system can't keep up.
Adding an electric fan probably blocks more air than it can produce while driving. A quick rise and boil over is a total lack of cooling or engine component fail.

Amazon sells digital thermocouple thermometers for cheap, they work really good for checking temps in hoses ( you can slip the thermocouple under a hose clamp or even under the hose into the coolant).

What is the water temp entering and exiting the radiator? A multi lead thermocouple thermometer will let you see this in real time driving.

A zero pressure radiator cap will let the coolant out the fastest, just one pound of pressure raises the boiling point 3 degrees. If the radiator can hold pressure, add a low pressure cap.

A mechanical temp gauge will always keep rising when the engine is shut down, the heat just doesn't go away when you shut off the engine. Mine goes up.

Does coolant run out of the block drain towards the rear of the engine? YES, block is probably clean. NO, you need more cleaning. A power washer with the RED pinpoint tip will break up the crude and blow it through the motor, so have the radiator hoses off and water pump removed, then blast though as many holes as you can. A garden hose is for rinsing it out, a power washer is for cleaning! It should have been cleaned out when it was rebuilt!

If the temp probe is in the head between two cylinders, it will read hotter than if it's under the thermostat. My 250 showed 20* hotter in the head before moving it to the thermostat housing.

Whats the idle rpm?
Can you feel air flow from the fan?
At high idle, can you feel air being pulled through the grill?
Is the pulley diameter correct for the water pump?
Is the fan blade correct, and does it have a decent amount of pitch to the blades?

Joe

Joe, thanks for all the info. I have not put more than a couple of hundred of miles on my rebuilt engine. My 48 Chevy came with a non pressurized radiator. I fill the radiator just to cover the core and not to the top to allow for expansion. I have installed a expansion reservior and even when I'm driving my truck some antifreeze ends up in the expansion reservior instead of on the ground. I've taken several temperature readings with a hand held electronic thermometer. Here's some readings that I have taken recently.
While running, at the Thermostat Housing 210 F
Upper Radiator Hose near Thermostat Housing 171 F
Upper Radiator Hose "Hose Clamp" near top tank 204 F
Upper Tank 204 F
Lower Tank 189 F
Lower Radiator Hose 166 F
Using my Hand held Thermometer and not the mechanical temp gage. Starting with a cool engine 99 F within 10 minutes my engine reached 214 F.
I have good flow through the drain valve located on the driver's side on the lower side of the block. What I can tell you is my engine has the original factory fan so it should have the correct blade angle/pitch, etc. The pulley is the original size, diameter. I agree with you that the engine should have been cleaned of course during the rebuilt but I can't verify that it was.
I like your idea of back flushing the coolant system to see if I get any rust flakes, etc. out of the engine.
I may back flush my engine first and if necessary run some Fleetguard Restore Plus a mild acid based coolant cleaner to see if that helps.

If you have a recovery reservoir, you need to fill the radiator to the bottom of the filler neck in order for your recovery tank to function properly. The tank will fill up when hot and return the coolant to the radiator as it cools down.

Keep a small amount of coolant in the recovery tank - at the cold line.

My 216 uses a 4 lb cap along with a recovery tank. It works like a modern car's system.

If I were you, I'd buy one of those head gasket test kits that uses blue fluid to test for CO2 in the coolant. They're only around $20 at the parts stores.

you put the test tube with the fluid over the radiator filler neck while the engine is running. A vacuum tube is connected to the vacuum port on the intake manifold.

If CO2 is detected in your radiator the blue fluid turns yellow.

This indicates that exhaust gases are entering your water jacket - most likely through a damaged head gasket.

This hot exhaust gas may be what is causing your engine's coolant to heat up so rapidly. If nothing else, it will rule out an exhaust leak into the cooling system and allow you to focus on other areas.

Otto,
If a person was adding an overflow tank on the firewall, should it be at a certain height in relation to the radiator?

Thanks, Glen

The exhaust gas test would be a good next step, my brother found a leaking head gasket on his Jeep with one of these. It looks like the engine is running around 210*, your tests confirm this, radiator is doing what it can, but only removing about 20* of heat. I don't know if thats good or not, never really looked into how much they should lower the temperature. Whats the tubes look like in the core? Your mild acid system cleaner might help if they have scale build up.

It also sounds like the engine is pretty clean inside since it flows out the drain. It seems that area of the blocks is where everything settles. Back flushing won't hurt. Maybe come up with a water and air pressure nozzle of some kind if you don't have access to a power washer, a piece of 1/4" brake line on a air nozzle that you stick in the block each direction with water coming in from the front of the block, at a minimum a coat hanger to pock around in the block.

It also sounds like the fan and pulley are right, a shroud would probably help some, but I doubt it would cure it. It worked as is for decades, so something is not right.

Try the test for exhaust gas.

Ponchog,

Generally speaking it should be about even with the top of the radiator. Take a look at your modern vehicles. Sometimes they are a little lower than the top of the radiator, sometimes they're a little above it.

Since it isn't gravity that's controlling the transfer of coolant back and forth, it doesn't make too much difference.

A previous owner had already mounted it in the position its in and I decided to leave it in place. Unfortunately for him he had the an incorrect style radiator cap installed which would not allow the fluid to return to the radiator after it was expelled.

Be sure your radiator cap has the poppet valve ( Nickle sized rubber valve in the center of the cap).

In these pictures, I have just driven 10 miles this morning and the engine is at about 180 to 185° and you can see that the coolant level is about halfway up in the container.

The last picture is about 6 hours later at 3:30 this afternoon after the engine has cooled back down to normal cold temperature. And you can see the coolant level in the reservoir tank has gone back down to it's normal level after returning the coolant to the radiator.

The temperature difference between the upper radiator hose inlet and the bottom radiator hose outlet should be about 20° to 30° if the radiator is doing its job properly.

Here's what I was talking about regarding the puppet valve in the radiator cap.

If your radiator cap doesn't have one of these little spring-loaded valves in the center of it, it won't work with a recovery reservoir

I have a recovery tank mounted down by my motor mount on my 250, fluid comes in the top through a tube that reaches the bottom of the tank, the over flow tube is just inside the tank and dumps on the ground if the tank ever fills up all the way. I used a 12" piece of 3" exhaust pipe, some 3/8" brake line. and some sheet metal caps. Its all welded together so I can't really see how much is in it, as long as it doesn't dump any out I'm happy. I do check the radiator every now and then. I don't believe it matters where you mount the overflow, thermo expansion and contraction should move fluid where it needs to go, though most are mounted level or just below the top tank. Our 2026 school buses have the tanks above the radiators, Ford trucks are level with the tops, and most of the commercial mowers we have are close to level with the top radiator tank.