340 Overheat / Radiator Geyser

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Inertia said:
On one of those trips, if you shoot the rad imput/output temps when hot, and we know the new rad is doing its job of shedding 50*ish, then we can eliminate that and try other stuff.
If the rad is 180* ish at the top, and 170+*ish out the bottom, that would be a problem.
The blow back is kinda like the pumps doing its thing creating pressure while running, then when shut off, the pump pressure shuts off, and surges back.
We need some help here.
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Upper hose at radiator = 202
Lower hose at radiator = 149
Thanks
 
This is the last of the troubleshooting that I’m gonna do on this thing before taking stuff apart. Not sure if I mentioned yesterday’s pressure test. As I said the gauge on the tool quit, but I manipulated it to get it to work. I can’t speak to the accuracy, but I cranked it up to 15 psi. After 30-minutes it dropped 2psi, but there was a visible small drip from a heater hose connection.

Today I ran the car at idle for 20 minutes then started taking temps. Temp gauge was at ¾ by this time and still climbing slowly. Heat is always hot. Gauge never goes up, then backs down as-if thermo was opening, so after all this maybe it’s just the thermostat.

Hose temps were taken at the clamps as someone suggested. These are original wire type clamps.

Upper hose at engine-212, at rad-202
Lower hose at engine-156, at rad-149
Upper tank at hose-206, center-206, R side-205
Thermo housing-210
Water pump housing-172

The 37 radiator “passages” ranged from 108 to 188 (suspicious?)

This time I left the radiator cap on. At 18 minutes I started to get some discharge from the cap overflow but not much. Upper hose did not feel firm until late into the experiment.

Phase II. I let the car cool for 2 hours.

Ran it for another 20 minutes, this time with the cap off. Did not take any temp readings because the thermometer quit altogether (overheated, ironically). Same results. Temp rose to ¾+. Coolant again dumped from the radiator after shutting down.

Remember guys, I have very limited resources at this time in my life. If I had even just a driveway to work in, I’d just pull everything and maybe send the radiator out, then go from there. I also can do grunt and detail work like nobody’s business, but I SUCK at diagnosing/tuning, stuff like that, that’s why I’m trying to get maybe some idea of how you think I should proceed with this thing. Sunday (Sunday…SUNDAY !!) I’m gonna try doing a good flush and replacing the thermostat, as well as testing the old one. Thanks again.
 
mitch340Duster said:
No change with behavior. No geyser of course, but very little loss from overflow hose. Thanks
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This actually sounds like it might be normal. Perfectly normal for the engine to heat up more as soon as it's turned off.
 
My 84 Prospector with 360 4bl did same thing. My memory sucks, but I believe the lower rad hose even collapsed temporarily. Pretty sure a tstat change fixed it. If you change it remember once assembled leave coolant out until RTV dries(if you use it)
Good luck.
 
Does the temperature go down at highway speeds or stay the same?

Didn't see where you mentioned what degree thermostat you have installed.

I would want to at least temporarily install a manual temp gauge to verify actual coolant temps.
 
mgoblue9798 said:
Does the temperature go down at highway speeds or stay the same?

Didn't see where you mentioned what degree thermostat you have installed.

I would want to at least temporarily install a manual temp gauge to verify actual coolant temps.
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1. I don't think so. It has not been driven over 30 MPH in a long time. For now, I just want to be able to cruise Lower Broadway, which is a sloooow drive with a lot of loooong lights.
2. I don't know. Probably 180. I'm installing a 160 Sunday.
3. Yeah I know. Like everything else, my aftermarket gauges are buried in storage somewhere. If I close on my property in the country Monday AND if the eviction of the current "tenant" is successful (my world), I'll be able to start setting-up a temporary garage and getting my stuff organized. It's also a 1/2 hour drive from here though.
4. Thanks

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Dicer said:
That is alot of big bubbles in the radiator neck....are the bubbles constant, maybe a quick test?
OEMTOOLS Engine Combustion Leak Detector
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That tool...I never sausage a thing. Good to know. I'm gonna stick with the current plan first of thermo/rad flush. I'll try the tool next if I need to. Now that you mention it I don't remember seeing the bubbling yesterday when I ran it. Thanks
 
mitch340Duster said:
1. I don't think so. It has not been driven over 30 MPH in a long time. For now, I just want to be able to cruise Lower Broadway, which is a sloooow drive with a lot of loooong lights.
2. I don't know. Probably 180. I'm installing a 160 Sunday.
3. Yeah I know. Like everything else, my aftermarket gauges are buried in storage somewhere. If I close on my property in the country Monday AND if the eviction of the current "tenant" is successful (my world), I'll be able to start setting-up a temporary garage and getting my stuff organized. It's also a 1/2 hour drive from here though.
4. Thanks

View attachment 1716302404
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I gotcha. Get the thing on the hwy cruising at steady 55 to 60 for a few miles. If the temp goes down, it would point towards a possible problem with the shroud or fan not being up to snuff at idle.

205-210 is normal for most newer stuff including the magnums run at. Wondering if you accidently have a 195 thermostat installed. I don't like my engines running that hot so I always put a 180 degree thermostat in my magnum engines. Even that didn't cool down my 5.9 in my van enough for my liking so I wound up installing a big capacity aluminum radiator and electric fan set up from a Dodge Intrepid. Big difference now it will cruise at 185 all day.

Good luck with the other stuff I have been in similar situations.
 
mgoblue9798 said:
I gotcha. Get the thing on the hwy cruising at steady 55 to 60 for a few miles. If the temp goes down, it would point towards a possible problem with the shroud or fan not being up to snuff at idle.

205-210 is normal for most newer stuff including the magnums run at. Wondering if you accidently have a 195 thermostat installed. I don't like my engines running that hot so I always put a 180 degree thermostat in my magnum engines. Even that didn't cool down my 5.9 in my van enough for my liking so I wound up installing a big capacity aluminum radiator and electric fan set up from a Dodge Intrepid. Big difference now it will cruise at 185 all day.

Good luck with the other stuff I have been in similar situations.
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Thank you...The 180 that was in-there tested OK. I installed a 160 just now and started the process of a radiator flush which I'll finish Sunday. Given the history of this car (started resto in 2006 and still not driveable), I'm "certain" that this is gonna be something much more sinister.
 
I would challenge you to put a real temp guage on it and read the actual temperature. I wouldn't be going by the factory dash gauge. Only n other thing not mentioned, is make sure your water pump pulley IS smaller than your crank pulley.

I think you're chasing your tail, personally
 
I had a dart that the lower radiator hose had plastic plug inside that caused the same problem
 
mitch340Duster said:
Yes I searched before posting. My 340 is a "fresh" motor but broken-in. The car has been plagued with issues so I'm just getting to where I can drive it more than just around the block. I've taken it out maybe 3 or 4 times and it's always been running real hot. 3/4 on the gauge or more. Tried some more defined troubleshooting today. After the last overheat last week, I topped-off the radiator. Today I cranked it up and coolant immediately discharged from the overflow hose. OK it was probably overfilled. After a while it stopped, but the temp quickly rose to 3/4 and hung right around there. Heat is hot. The radiator cap was OFF from this point on. There's some bubbling in the radiator but the level remained consistent. Another thing I noticed was it seemed like it wasn't circulating. There were a few specks of orange engine paint in the coolant that stayed right there at the opening the entire time. I let the car idle for 35 minutes and there was really no change. The gauge would creep up to just over 3/4 at times, and when increasing RPM's the temp dropped a little. HERE'S WHERE IT GETS GOOD...As soon as I shut it down, the radiator exploded like Old Faithful from the filler opening. Probably a 2-foot geyser. So bad that it would have been catastrophic if any of you goons trying to help had been peering down into the radiator. It blew out a lot of coolant, and then I could hear boiling from the motor.
This is a stock 340 rebuild. Recored radiator. Oil looks good. No steam from tailpipes. Has a fan clutch but the fan spins all the time. As I said I've had a real hard time getting this car to where it can be driven, and it's been a long time but I really think that this problem is not a "new" one, rather it has been this way since the rebuild.
I have no confidence that it's something like it being airbound, but only because I've had small block Mopars for 40 years and never had to deal with any of that. Thanks, guys !!
I do have IR thermometer data and video of the bubbling and the suspected lack of circulation if anyone wants to see it.
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Sounds like either your thermostat is NFG or you have the head gaskets buggered up. Pretty obvious you're not circulating coolant.
 
AJ/FormS said:
There is a MINIMUM of one girl for every guy in this world. You may have already met her, but maybe have already rejected her.
-----------------------------
You like stories? Brace yourself.
I met my wife in mid-December of 1975. I was already 22, to her 18. I rejected her. Too skinny, hair too short, Christian roots. Never thought about her again for maybe four months. Five months later, just after her 19th Birthday, spring of 1976, we shacked-up and a year later (April-1977) got married. Babies started coming in 1980/82/84. Last one left home in 2004. Eventually(mid 90s) we both became Christians.( me first for the win) We're still together, some 48 years later.
You never know the turns your life can take.
----------------------------------------
Here's an example;
Abraham lost his wife around age 130. Almost Immediately he took a new wife, who bore him another 6-pack of kids. Then he died at age 175.
Now think about that, Keturah produced six kids. (actually I seem to remember six sons and a daughter)
We know that today, women usually have lost all their best seed by age 40, and Sarah, Abe's first wife, barren her whole married life, laughed when told that she would have a child at about a hundred years old, implying that she was long-ago dried up. But nonetheless, Isaac was born nine months later.
Now, try not to imagine Abe and new-wife Katie, in the cool of the night, Abe being between three to four times as old as his new bride. Yeehaw!
The point is that you just gotta see something supernatural in that marriage. Abraham, obviously, was much loved.
You want a wife, just ask the spirit in the Sky who knows exactly where she is.
Give a testdrive to; John 14:10>15; Then keep your eyes peeled.
Oh yeah, stay out of the bars. Every guy I know who ever pulled a bride or brides, out of a bar, it went sour in a hurry. Two of them are on their Third wives.
>>Here's a hint; go check out your Cousins.
I didn't know it at the time, but over four decades later, we found out, that my wife and I are Fourth cousins. Suuuuuupernatural!
>>Noah's three sons, all blood-brothers, married sister-girls, fathered possibly by their grandfather, Methuselah. I think that would make them cousins once removed.
You think that there's any way that such a thing could NOT have been supernaturally orchestrated?
>> there is a sweetheart out there looking for you.
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Kissing cousins, growing up we had a couple in the family. Several times removed, nothing wrong with that.
 
"Final" update for now. I took it on the highway yesterday. Took 10 minutes to get there, then after about another 10 at 60MPH, same deal. If anything it heat up quicker on this drive than it does when sitting idling. When home and cool I did a very thorough coolant flush. There was a lot of **** inside the end of one of the heater hoses. This thing is very consistent. After 30 minutes the temp gets to just over 3/4, engine stalls, coolant relieves from overflow hose, sound of boiling. I failed to mention that after it gets hot, the metal dash is so hot that you almost can't touch it. For yesterday's drive I had the heat off and as I said I feel like the car heated up quicker. Maybe the heater core is trying to do the radiator's job?
SO...It's pumping water. With the radiator level just below the baffle I can see the water moving. 160 thermostat is new and tested. No obstructions in any of the hoses. Fan turns all the time, it has a shroud, radiator was recored but a looong time ago and the car mostly sat since then. The bubbling of coolant that you saw previously is not happening anymore.
The only temps I am happy with are at the lower hose, which is 150-ish. Everything else is running 180-200 or more.
The next thing I'm gonna try is the combustion leak tool and see if anyone rings-in about the lower hose being an acceptable (?) temp while everything is hot, and maybe see about having the radiator boiled-out, but it's easier to find a nickel bag than it is a radiator shop anymore. Can they test them for flow? In other news, after all of this yesterday I got the news that the as****e squatter still has not vacated the house I'm buying so the closing has been pushed from today to Friday. It was already postponed by 2 weeks. The Sheriff is involved now, but "this I can tell you", after a 2-year search for property, this purchase is never gonna happen, so the clock is likely gonna get turned back another 2 years after Friday. This car may never see a garage again.
 
After reading everything, I keep thinking of the impeller slipping on shaft of w/pump when warmed up. Also, fan not mounted backwards? I really thought the new t-stat would’ve fixed it.
 
It may be time to remove upper and lower radiator hoses and thermostat and check them all out if ok then remove the water pump to see if the impeller is broke or loose
 
The slipping impellor deal can be checked by pulling the by-pass hose off the timing cover and slide a tool with a bent end as in pic, you can hook, or jamb the impellor to check if it's secure to the shaft.
As mentioned, the rad is shedding enuff, if it were mine, put the cap on, tape over the gauge, and drive it for a week.
jmo, good luck .

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Last edited:
68Bee said:
After reading everything, I keep thinking of the impeller slipping on shaft of w/pump when warmed up. Also, fan not mounted backwards? I really thought the new t-stat would’ve fixed it.
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Darn it I keep meaning to see if the fan is backward but I always forget.
 
Regarding your squatter.
I was a landlord for a loooong time.
Courts couldn't get em out. power, water had been off for months.
Wife and I were watching TV one nite saw story of landlord taking baseball bat and busting out squatters (his) windows.
My wife didn't scream long or loud enuff as I grabbed my 9 iron going out the door.
Smashed out every window, winter . .
They were gone in 2 days.
Place was a wreck, but was before anyway.
Funny side note, - they were old single glaze/pane windows needing upgrade anyway .
 
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