340 Overheating Help

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sportsuburbangt

sportsuburbangt

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I have a 340 that i just had rebuilt. It was bored 30 over, 9.75 to 1 compression, and I am using an edelbrock rpm airgap manifold. I have it in a 72 dart, when the motor heats up the stock dash temp gauge is at the bar before 250, it stays there and does not go past the bar. I put the end of a mechanical temp gauge in the top tank of the radiator and it stays at 200.

I have replaced the radiator with a US radiator 22 inch 3 row unit, i put a new fan clutch (hayden Jag unit), I am using the stock shroud, I tested the thermostat and it opens. I also ran the motor with a different thermostat and no thermostat and the same thing happens.

The motor does not crank when it is hot, i have a mopar mini starter on it.

I took it for a drive tonight about 3 miles an the gauge stayed at the bar before 250 on the stock gauge. When I got home the gauge was on 250.

Any thoughts on this, tomorrow i am attaching a mechanical gauge to the motor to see whats up.

Thanks Mike
 
I would check the easy stuff like a stuck thermastat, hoses sucking shut, etc Are you using the original v-belt pullies or did you change over to serpintine belts in other words is the pump the turning the right direction? Then I would have the radiator dye tested to see if exhaust gases are in the radiator meaning blown headgasket, cracked head or?
 
It could be your running lean at part throttle cruse or you might need more advance. Retarded timing and a lean carb will both cause higher temps. What is the rest of your build like? How do you have the dist set up?
 
For starters get a good gauge on there. Factory gauges can be hit and miss, especially 40 years later.
Keep in mind a fresh rebuild usually will run a little warm until broke in.
There is a long list of things that can make a car run hot.
Going to have to start checking off the list.
Examples
Running lean,to much timing,clogged radiator,radiator cap,to small radiator,dragging brakes
ect.
 
200' is not too hot. but you need to install a good gauge and see what it's getting up to while driving around and parked. all the stuff Johnny Dart listed are great things to check. but first you need to know if it's even hot

good luck

p.s. how about some pics :)
 
I'm running the stock belts, rad is new, cap is new, thermostat is good(tested in boiling water), and no water in the oil.
I'm also attaching a few pics.

Thanks for all the responses, im getting a real gauge tomorrow.
 
Dart Pics
 

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sportsuburbangt said:
I'm running the stock belts, rad is new, cap is new, thermostat is good(tested in boiling water), and no water in the oil.
I'm also attaching a few pics.

Thanks for all the responses, im getting a real gauge tomorrow.
Click to expand...

Oil in the water and exhaust in the radiator are two different problems. But hopefully you have neither.
 
i'm running 10 30 brad penn oil, i am putting the light on it today to reset, i have been backing the timing off ever since this problem started.
 
I'm thinking 3 things, timing, collapsing lower hose, or lean condition.

New rad, new clutch fan, and shroud were good steps. My clutch fan was slipping giving me problems. It wasn't that old either.
 
The old rule I was told (and this is just one of those old timer things.....) Give it a hard spin by hand and if it goes around more than 5 times the clutch needs to be replaced.
 
it was just rebuilt March 2010, i had it broken in on the dyno. I have put 3 miles on it, all last night. It took almost a year to get it installed and hooked up. I have a 3 year old and another on the way. I'm amazed i have been able to get any of this done at all.

I have a spring ready to go for the lower hose. I will be doing the lower hose spring, timing and gauge this afternoon. As soon as i am relieved from babysitting duty.
 
I think the guys covered it all, I just gave their 3 best choices based on what you've done.


A new rebuild will run hotter until it breaks in. Do the timing first, adjust the carb, you have the hose spring. Try and find a good temp gauge too. I assume you are running about a 180 thermostat. Good luck.
 
Another thing to check , if your running a vacuum advanced dist. it could be advancing it too much, when i checked mine at cruise it was advancing the timing to like 55 deg., which was making it run hot while cruising. Just a thought. theres an alen head inside there you can turn to set it with.
 
hmmmm I am thinkin that vacuum advance may be useless with todays fuel? that may be your problem.... the extra advance is no longer necessary and todays fuel typically runs hotter for some reason...sumtin to think about
 
STOP!!!!!

If you are getting a 200 degree reading inside the radiator, most likely everything is OK and the gauge is your problem.

Start the car while it is "overnight cold" and feel the upper hose near the radiator neck while someone watches the gauge. You could also set up a mirror to watch this for yourself. Look where the needle is when the hose gets hot. If you have a 180 thermostat, the needle will be indicating 180 when the hose gets hot, as this is the thermostat opening for the first time.

You could also try an infrared temp gun, if you know anyone with one. Aim it at the upper hose or thermostat housing while the motor is running and up to normal temp.
 
What is your total timing?
What is your idle timing?
What cam do you have?
What is the lobe sep on your cam?
Is it degreed in?

Is all the air bled out??

I bleed my air by pulling the front EX manifold studs and filling it through the Tstat housing, but sometimes air will hang around in the passengers head and cause issues.
 
this is getting old; buy a gold, and jump up, even if you have no clue.
Pull the rad and have it tested for flow, at local shop. If good, start at therm, drill 1/8" in plate, to eliminate burp. Replace the gauge/try a different one. Yeah, use a harbor freight gauge, and check.
If it's not spewing, it is gauge.
 
I ran it tonight with a sun gauge i bought from pepboys. Its reading a solid 180 degrees.

It's the gauge in the dash that is the problem, i'm thinking the sending unit. I installed a new sending unit when i installed the motor. The dash gauge is on the hot bar, and the sun gauge is at 180.

It still will not start hot, but i think there's something wrong with the starter. Thanks for all the pointers and tips. This forum is the best!
 
Aha....The 40 yr old gauge letting us down again.. How rare. Lol
Glad you found the problem.
Sounds like it is time for a new starter. Look into a mini starter. They work much better.
 
Johnny Dart said:
Aha....The 40 yr old gauge letting us down again.. How rare. Lol
Glad you found the problem.
Sounds like it is time for a new starter. Look into a mini starter. They work much better.
Click to expand...

just sharing info: a quote from the very first post in this thread

"The motor does not crank when it is hot, i have a mopar mini starter on it."

I cannot stand Mini Starters, to me they are all expensive junk!!! IF I was given one I would throw it away. cannot see burdening someone else with junk like that!! IF you at all can replace that mini starter with a full sized SHORT Mopar starter...chances are your car will start hot or cold, unless your headers touch the starter, THAT can be an issue
 
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