My 340 is running hot I think.. I need a sanity check.

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AlV

AlV

Crabs in a barrel
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Greetings,
I've finally got to the point where I have my GTS on the road and now working out the bugs.
One of the more persistent issues is temperature with the 340. I thought I had it licked but It's still acting funny. When I go for a ride the Stewart Warner temp gauge says 185 and the factory temp gauge points straight up and reads 1/3 of the sweet spot, the gauges read normal but the engine seems hot and I hear the coolant burping around. I have no over flow bottle so the tube goes from the neck to under the car. Today I was leaving a trail of coolant drops as I was coming up the driveway.

I can't barley touch the rad even after it's sat for a while.
Top radiator hose has pressure lower isn't collapsed (at least when I look at it)
When its cold it starts right up. after a drive and the temp heats up it doesn't want to start.

Rebuilt engine 69 340 (It's a mild stock build)
Reconditioned crank and rods, .40 over, stock 340 "X" heads, Comp XE275 cam, Performer RPM 340/360 (non-EGR), Holley Avenger 670 w/ e-choke carb, Stock HP manifolds, stock valve train, MSD Billet Distributor w/6A
Compression: 10.5:1
Timing: initial 20 with 35 total
Plugs: are Gapped at.040
Idle: cold 800 rpm warm 500 rpm
T stat: 160 with 1/8th drill
Fan: factory 7 blade with viscous clutch.
Coolant: 50/50 mixture Tap water/coolant

What am I missing?
 
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For starters factory gauges are not all that accurate, and only offer a range of what's acceptable. If the needle is near center "in the band", it's okay. After market gauges aren't much better, but at least have numbers that can be within a few degrees of an accurate or test gauge. My feeling is there's still in the system. Point the nose of the car uphill, and run it to expel air.
 
If you don't have a recovery bottle and you fill the radiator to the top, guess what happens with the engine get hot and the water expands? Yep It goes out the overflow. You keep filling it up, it keeps pissing it out. So first you need a coolant recovery system to stop that. That also prevents air in the system when the water finds its own level and blows out the overflow. That's why old cars have rusty water because of the air in the system. Coolant recovery prevents that
 
Yes, I have a shroud.

I'll have a temp gun tomorrow. still would be odd for both to have the similar reading.

Don't recall seeing the SB 340 coolant overflow. does anyone have a picture of the setup?
 
Overflow tanks came along somewhere in the early 70s, and at the same time, two-part radiator caps. One piece caps do not let coolant blow as easily, and level is supposed to be one inch down from top, not "full", to provide for expansion.
My 71 and 72 did not come with overflow tanks. Are you using a cap where the center is a separate loose plate?
Does the gas gauge read high also?
If so there may be an issue with the regulator on the instrument cluster.
But anywhere in the " normal" range is considered acceptable.
Use the infrared gun, and just notice where that gauge reads at 180 and mentally note where that is on the gauge.
 
160 sounds way too low, not that this would have anything to do with overheating though, thermostats only set the minimum temperature not the max.


Check your plugs and make sure you are not running too rich or too lean.
Run it with the cap off, when it is cooler, and observe the water flow to make sure you are getting good circulation.
 
Darthomas said:
Overflow tanks came along somewhere in the early 70s, and at the same time, two-part radiator caps. One piece caps do not let coolant blow as easily, and level is supposed to be one inch down from top, not "full", to provide for expansion.
My 71 and 72 did not come with overflow tanks. Are you using a cap where the center is a separate loose plate?
Does the gas gauge read high also?
If so there may be an issue with the regulator on the instrument cluster.
But anywhere in the " normal" range is considered acceptable.
Use the infrared gun, and just notice where that gauge reads at 180 and mentally note where that is on the gauge.
Click to expand...

yes I am using a 16 lbs cap with the loose center valve.
The gas gauge reads 1/4 tank but that seems right. I recently replaced the voltage limiter with a RTE digital unit. I am fairly confident both temp gauges are working.
 
trapster said:
160 sounds way too low, not that this would have anything to do with overheating though, thermostats only set the minimum temperature not the max.


Check your plugs and make sure you are not running too rich or too lean.
Run it with the cap off, when it is cooler, and observe the water flow to make sure you are getting good circulation.
Click to expand...
I was fooled as youngster, thinking I saw "enough" circulation to cool properly.
Radiators can sometimes be cleaned of corrosion, if there's enough flow.
CLR can remove a lot of it, but I think it has
finished off the water pump seal for me when I used it. Maye take the radiator off, flush, then put the cap on, set it down on its face, then fill it with a gallon if CLR and wait a day or 3.
 
AlV said:
Yes, I have a shroud.

I'll have a temp gun tomorrow. still would be odd for both to have the similar reading.

Don't recall seeing the SB 340 coolant overflow. does anyone have a picture of the setup?
Click to expand...
7712776-MoparsInMay13Sm054.JPG
 
trapster said:
160 sounds way too low, not that this would have anything to do with overheating though, thermostats only set the minimum temperature not the max.


Check your plugs and make sure you are not running too rich or too lean.
Run it with the cap off, when it is cooler, and observe the water flow to make sure you are getting good circulation.
Click to expand...

My understanding of the Thermostat operation is that 160 is the point where the stat starts to open but the temp can be higher than that. Tha'ts been my observation

The coolant is 1 inch below the cap neck and very good flow can be seen with the cap off.

I have to get an infrared gun.
 
One cheap check is to hose water onto the radiator when it's running and see how it dries off, clogged tubes and sections dry last.
 
AlV said:
Greetings,
I've finally got to the point where I have my GTS on the road and now working out the bugs.
One of the more persistent issues is temperature with the 340. I thought I had it licked but It's still acting funny. When I go for a ride the Stewart Warner temp gauge says 185 and the factory temp gauge points straight up and reads 1/3 of the sweet spot, the gauges read normal but the engine seems hot and I hear the coolant burping around. I have no over flow bottle so the tube goes from the neck to under the car. Today I was leaving a trail of coolant drops as I was coming up the driveway.

I can't barley touch the rad even after it's sat for a while.
Top radiator hose has pressure lower isn't collapsed (at least when I look at it)
When its cold it starts right up. after a drive and the temp heats up it doesn't want to start.

Rebuilt engine 69 340 (It's a mild stock build)
Reconditioned crank and rods, .40 over, stock 340 "X" heads, Comp XE275 cam, Performer RPM 340/360 (non-EGR), Holley Avenger 670 w/ e-choke carb, Stock HP manifolds, stock valve train, MSD Billet Distributor w/6A
Compression: 10.5:1
Timing: initial 20 with 35 total
Plugs: are Gapped at.040
Idle: cold 800 rpm warm 500 rpm
T stat: 160 with 1/8th drill
Fan: factory 7 blade with viscous clutch.
Coolant: 50/50 mixture Tap water/collant

What am I missing?
Click to expand...
The t-stat is too cold. the t-stat is wide open, coolant flow is high and not getting cooled in radiator.
 
your temp is 185,that's great.
There isn't anybody that can hold their hand on a 185 degree rad.
... those heat guns are very innacurate
 
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I once had a 71 Demon that made a lot of gurgling noises in the heater-core. The hoses were on backwards, and I suppossed that a big bubble of air got trapped inside it. I flipped the hoses around,and all was quiet.This core had 2 same-size pipes on it.Only Mope I ever had that did that.
 
Heater hoses hooked up backwards also kills heater performance in winter, as the heater core is only half full most of the time.
 
AJ/FormS said:
I once had a 71 Demon that made a lot of gurgling noises in the heater-core. The hoses were on backwards, and I suppossed that a big bubble of air got trapped inside it. I flipped the hoses around,and all was quiet.This core had 2 same-size pipes on it.Only Mope I ever had that did that.
Click to expand...
Good thought, I double checked and it appears that the heater has good flow and I've tested the heater valve to ensure that I had purged the core.
Heres apicture of the heater hose setup. Does it look correct?

Thanks!
AlV

engine.jpg
 
As said, your coolant level will not stay any higher than 1" or 1-1/4" below the top of the tank in the radiator (not below the top of the cap neck). If you over fill it, it will blow off coolant 'til it has enough air space for expansion. So let it blow off and see where it settles to.

Where is your 2nd temp sensor for the Stewart Warner gauge installed on the engine? The reading sounds pretty good if the stock gauge is midway.

FWIW, the heater hose connections are backwards at the firewall compared to a '65 Cuda....if that is the same as your later model.

And BTW, you ought to drain all your coolant and get rid of that tap water. If it is softened water, that may OK. But regular tap water typically has minerals that will cause considerable deposits and contribute to block and head corrosion (in the case with a brass rad). Distilled water should be use.
 
You said that the lower hose isn't collapsing when you look at it idling, but it may be a much different story when highway driving or quickly accelerating. Grab it when it's cold and squeeze to feel the interior anti-collapse spring. If you don't feel the spring, it is missing and is definitely collapsing on you.
 
Did someone exactly calculate you compression? Cc'ing the heads, measuring installed piston to deck clearance, etc?

What part number Pistons do you have?

IMHO, true 10.5:1 compression is too much for modern 91 octane gas.

Have you tried backing down the timing to 33 deg total?
 
nm9stheham said:
As said, your coolant level will not stay any higher than 1" or 1-1/4" below the top of the tank in the radiator (not below the top of the cap neck). If you over fill it, it will blow off coolant 'til it has enough air space for expansion. So let it blow off and see where it settles to.

Where is your 2nd temp sensor for the Stewart Warner gauge installed on the engine? The reading sounds pretty good if the stock gauge is midway.

FWIW, the heater hose connections are backwards at the firewall compared to a '65 Cuda....if that is the same as your later model.

And BTW, you ought to drain all your coolant and get rid of that tap water. If it is softened water, that may OK. But regular tap water typically has minerals that will cause considerable deposits and contribute to block and head corrosion (in the case with a brass rad). Distilled water should be use.
Click to expand...
Clarification, my fluid level is from the top of the tank not from the neck. See pic. Sorry for the confusion.

The sensors are an inch apart SW on the right factory on the left. In pic.

Dang you all are right about the heater hoses. I double checked the manual and this is why I need a sanity check. See pic. I'll swap them to ensure the are correct. Can that really be the root cause??

image.png


image.png


image.jpeg
 
autoxcuda said:
Did someone exactly calculate you compression? Cc'ing the heads, measuring installed piston to deck clearance, etc?

What part number Pistons do you have?

IMHO, true 10.5:1 compression is too much for modern 91 octane gas.

Have you tried backing down the timing to 33 deg total?
Click to expand...
Yes, my engine builder did the machining and spec'ing. We're using Sealed power 428P pistons.
I'll drop him a line to confirm.
 
Just a little something I'll toss in.

No, the heater hoses will make (almost) zero difference in the cooling of then engine.
Make sure your cap doesn't have any little cracks in those two rubber seals, as you are actually using a recovery system type cap.
And that my car runs 195-210 regularly on hot days and I'm fine with it, and I run a 190 stat in it.

If it gurgles and/or pukes fluid after you shut it off is when you start getting concerned, and in my own opinion they should all have a coolant recovery system to keep as much air out of the coolant as possible.
I made one out of a Shotgun shell looking thermos and plumed in from the bottom so it is nice and clean looking and IF it ever pushes coolant out and overflows the bottle it also comes out the bottom because I drilled a vent hole between the two inner metal layers of the bottle.

One other thing to mention is drilling a 1/8 air bleed in the thermostat solves the air bubbles when filling problems.

Not that you haven't done any of the above, but just notes.
 
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68gtxman said:
You said that the lower hose isn't collapsing when you look at it idling, but it may be a much different story when highway driving or quickly accelerating. Grab it when it's cold and squeeze to feel the interior anti-collapse spring. If you don't feel the spring, it is missing and is definitely collapsing on you.
Click to expand...
It's a new lower with a spring in it. I can feel the spring when I squeeze.
 
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