273 Overheating

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74Dusted

74Dusted

Stock Piler of 340's
Joined
Apr 11, 2011
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Location
Lewistown, PA
It's not a Duster (pretend it is), it's my D50 4x4.

Specs : 273 Small Block, Bored .060 Over with Forged Dome Pistons, .500 Mechanical Lift Cam (manufacturer unknown), 340 J (1.88 valve) Heads, 10.1:1 Compression, 340 Spreadbore Intake, 800 Thermoquad carb, 1971+ LA Timing Cover, Balancer & Water Pump. 22" A-Body Radiator, External Transmission Cooler, Mechanical Fan + Electric Pusher Fan. Mechanical
Gauges.

It didn't used to overheat, when I had a badly leaking 26" C-Body Radiator in the truck. Swapped in a like new (Spotless inside, not even a speck of dirt) 22" A-Body Radiator and ever since it's ran hot. Coincidence? Probably

We're talking 230+ degrees and still climbing.

First thing that came to mind was the Thermostat, I pulled it out and sure enough it was stuck shut. Didn't have another one on hand, so I put the water neck back on without a T-Stat to see if it made a difference. Nope, still overheats (odd, I thought for sure the T-Stat being junk was the cause). Pulled the Radiator Cap to check for circulation, coolant is circulating through the radiator.

Ok, maybe it's circulating too fast without the T-stat and doesn't have a chance to cool down. Put a new (tested in a pan on the stove) T-Stat in, functioning, still overheats.

Ok maybe it's Airflow? Wait, the mechanical fan is drawing enough air to spin the electric fan full speed (without it turned on), and it doesn't matter if it's idling or running 65mph it still overheats. At 65mph it wouldn't matter if the fan was drawing enough air. So it's not an airflow issue.

Maybe it's the timing? I was screwing with the timing a while back, hoping it was a tuning issue. So I grabbed the timing light and tried setting the timing in various places. Tried Everything from 28* to 34* at Full Advance (3k rpm, give or take 100-200 rpm) with the Vacuum Advance Canister disconnected. No Improvement, it still overheats.

Maybe it popped a head gasket? No Oil in the Coolant, No Coolant in the Oil, it's not consuming coolant. Pressurized the cooling system to 20psi and left it sit for 2 days, it held pressure the entire time. Ok, maybe a Leakdown test. No, it's not showing any problems there either. (I still have to run a compression test as well)

Maybe it's crud in the cooling system? Flushed the whole system, 3 times, saw nothing but clean flush come out.

Other than overheating (idling or driving), the truck runs perfectly. And it didn't used to overheat. It used to run 190*, no matter what, except for when I would tow with it, then it would get up around 205*

Any ideas on why it would start overheating now?
 
74Dusted said:
It didn't used to overheat, when I had a badly leaking 26" C-Body Radiator in the truck.

Any ideas on why it would start overheating now?
Click to expand...

If it did not overheat with a 26'' radiator, put another 26" radiator back in.

Sounds like the 22" does not have enough core surface or fulid capacity to do the job.

Herb
 
I was hoping I didn't need another 26", because I had to butcher the previous 26" to get it to fit the truck (by the time I was done, it was closer to a 23" radiator). I had to remove the Mounting Brackets, and cut 2 rows of cores off on both sides of the radiator to get it to fit between the headlights.

Old Radiator :

Where the 22" A-Body Radiator bolted right in, no mods to the radiator (just drilled holes in what was left of the core support and fabricated some mounting brackets to match up to the radiator)
 
if thermostat was stuck shut, i bet you that water pump is gone bad...

just my opinion. especially if you run her hard. my 340 dart would require new water pumps every so often because of owner lead foot abuse lol.
 
Sadly it wasn't the water pump.

Still overheating. The water pump I pulled off looked fairly new and there was nothing wrong with it (Standard / Non-AC). I had a brand new AC / Heavy Duty Water Pump here for one of my 340's, so I installed that on the truck. Thinking maybe I needed something a little more than a standard pump

Still wants to overheat.

Radiator Cap looked kinda ancient, so I put a new one on. No difference

Pulled the New Thermostat out, to see if maybe it had gone bad already, nope, no difference with it out either.

While I had the water pump off, I took a peek inside the cooling passages, clean. Knocked some of the freeze plugs out and checked inside the block, clean. Replaced the freeze plugs I removed, filled the system with coolant. It's circulating, (exactly the same as it was with the Standard duty water pump), but I've noticed it doesn't circulate nowhere near as well as my 6-71 Blown 340 Duster does in comparison

On the D50, coolant moves slowly across the radiator as the engine is running. On the Duster, it's moving fast enough to look like the pump outlet on a swimming pool. (and the Duster runs about 185* all the time).

Hmm, maybe something is plugging up a cooling passage somewhere? I flushed the system again. No change.

I've run out of things that could possibly be wrong.
 
While hot and running,, if you have a heat gun,, check the temps of the radiartor INLET/OUTLET fittings, (not hoses), there should be 30* - 50* diff between the two..

If no heat gun,, hot and running,, touch the front surface of the rad, (I use the back of my knuckles) about mid way,, all across the rad,, if you find any cool areas,, those are plugged tubes not flowing hot water..

The larger the cool areas,, the bigger your blockage..

hope it helps
 
74Dusted said:
Ok, maybe it's circulating too fast without the T-stat and doesn't have a chance to cool down.
Click to expand...
I hear that theory bandied about a lot on auto sites. Sounds like an exotic scientific phenomenon, but you will find nothing similar in any engineering heat transfer book (my M.S. thesis was in heat transfer). If adding a flow restrictor improves cooling, it is for another reason like preventing pump cavitation or redirecting the flow, not that the coolant is "moving too fast to cool". As a kid, our 63 Valiant boiled over on the highway. A workman nearby looked at it, saw no flow, removed the T-stat and found it stuck shut, put outlet back without it and we continued with no more over-heating. Said one doesn't need a T-stat in Florida (not totally true).

Do you have any indication of "overheating" other than your temperature gage? Has it actually boiled over? You can buy a radiator cap w/ built-in temp gage on ebay. Try that, or an IR gun.
 
Never knew that about the "circulating too fast" bit.

I back flushed the entire system, back flushed the engine & radiator separately, ran flush chemicals through the system. (didn't get anything but clean water out each time. Water flows through the radiator as fast as you can pour or pump it in.

Radiator seems to be an even temperature across the cores (by touch, can't find my infrared gun to check core/inlet/outlet temps).

Mechanical Gauge reads 225* (and will continue to slowly climb if you let it run)

Electrical (Factory) Gauge reads Pegged as far as it'll go.

Digital Thermometer/Probe measures 215* when stuck into the fitting for the mechanical gauge (I dunno if a 10* difference is a flaw/inaccuracy with one of them, or if it's the difference between actual coolant temp and a measurement taken from the other side of the brass fitting).


Note : I'm not a brave enough man to use that Digital Probe to measure the Inlet & Outlet Temp on the Radiator while the engine is running, since the fan blades are only about 3/4" away from the Inlet & Outlet.


Like I said, it'll continue to climb in temperature, but doesn't seem to boil over.


Leakdown Test showed nothing, head gaskets seem to still be holding on for dear life. Pressurized the cooling system, it held 20psi for 6 hours, without dropping so much as 1psi.


I'm about ready to just say screw it and run it to see if it'll stop rising after 230-235* Normally I shut it down, fearing engine damage if it climbs any higher.
 
I'm guessing this 22 inch a-body radiator is the problem. We cant see how badly clogged they are unless we take the tanks off. Just a guess though.
Good luck with it.
 
Man, that sucks. I really wasn't looking forward to sourcing a new radiator for this creature.

Last year Challengergary and I were discussing a Champion Aluminum Radiator for my truck, and he had no luck finding one that would fit my truck. They were all too tall and or too wide. It's a tight fit in the truck.



 
Check the plugs to make sure your fuel mixture is ok a too rich or too lean mixture could cause an overheating problem.

As for the water flowing too fast through the radiator, I don't believe in that either.

And remember the thermostat's job is to keep your engine from running too cool, the radiator's job is to keep it from running too hot.
 
I'll check the plugs later today, I dropped the truck off at my dad's place and picked up my 6-71 Blown '73 340 Duster for something to drive over the weekend.
 
What about a fan shroud? Are you running a shroud?

How far in/out of the shroud is the fan?

a shroud will help direct the air through the radiator to help cooling. You don't want the air to find a way AROUND the radiator, you want it THROUGH IT...


Have you tried running a garden hose through the radiator fins when it's overheating to see if it will cool the engine down. Water can take away much more heat than air and faster. See if that makes any difference.
 
trapster said:
Check the plugs to make sure your fuel mixture is ok a too rich or too lean mixture could cause an overheating problem.

As for the water flowing too fast through the radiator, I don't believe in that either.

And remember the thermostat's job is to keep your engine from running too cool, the radiator's job is to keep it from running too hot.
Click to expand...
X2
I have every cooling device known to mankind on my car. 26" aluminium rad, Brass Works HP water pump, transmission goes through a separate cooler ( not connected to the rad at all), engine oil cooler, 7 blade mechanical fan and a electric pusher fan and STILL it ran hot. I found that not having a seal on the hood to radiator support infected the cooling dramatically when idling with the fiberglass hood on. The biggest improvement cooling was when I installed a air/fuel radio gauge and got my fuel mixture dialed in. What an improvement! Runs better and is 10 degrees cooler in traffic. Good Luck
 
krazykuda said:
What about a fan shroud? Are you running a shroud?

How far in/out of the shroud is the fan?

a shroud will help direct the air through the radiator to help cooling. You don't want the air to find a way AROUND the radiator, you want it THROUGH IT...


Have you tried running a garden hose through the radiator fins when it's overheating to see if it will cool the engine down. Water can take away much more heat than air and faster. See if that makes any difference.
Click to expand...

No room for a shroud, see the pictures a couple posts above yours.

The fan blades are roughly 3/8" away from the Radiator. With no spacer between the fan & water pump.

The only way I could see a shroud fitting, would be a perfectly flat plate of steel or aluminum with a hole cut in the center for the fan to sit in. Wouldn't that restrict airflow, since it'd be hitting a "wall" instead of being funneled toward the fan?


I can try to seal the radiator to the truck a bit, about the only places where I have any metal to attach to is the headlight buckets. The top tank & cap sit tight against the outer skin of the hood (had to cut and bend the inner skin of the hood to clear the top tank and cap).

I'll let you guys know how things go. And just to be clear (better safe than sorry), I'm not trying to be rude with any of my replies, so if they appear to come across that way, I'm sorry.
 
A shroud it pretty much out of the picture at lower road speeds and can be a small restriction at higher road speeds. Unless shroud means something different than I normally think.....

Make sure you seal ALL gaps in the core support; I see some gaps at the top on either side of the rad in your pix..... I can think of one other thing you can try to explore another possibility after sealing the rad-to-core and rad-core-to-hood better. See if you can remove the hood bolts and put some longer bolts in with 1/2" to 3/4" spacers or stacks of washers between the hood and hinges. That will create an air gap at the back of the engine compartment to allow more overall airflow. This is not intended to be permanent but will be a partial test of better airflow through the whole engine compartment. (FYI, I have actually done this permanently on a turbo rally car to help underhood temps; it worked well in that case. It seems to allow both more rad air flow and air up around the engine too.)

If your temps do not drop with this and the rad/core sealing at road speeds, then you very likely just have too little coolant flow or rad surface.
 
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