Re: 340 running hot (long)
[Re: ozz383]
#743203
07/07/10 11:19 PM
07/07/10 11:19 PM
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Joined: Aug 2005
Posts: 1,043 Motown, Mi
PAULS_340
super stock
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super stock
Joined: Aug 2005
Posts: 1,043
Motown, Mi
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I have a very similar setup with my 340 Demon and it is so hot I can hardly work on it after a cruise. I removed the headers, still hot. Ironically, it doesn't overheat. I took the thermostat out, nothing changed. If someone told me a pure stock 340 wouldn't be so hot, I would trade engines.
Still looking for LM29H1B415501, '71 Demon 340
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Re: 340 running hot (long)
[Re: ozz383]
#743208
07/08/10 09:08 AM
07/08/10 09:08 AM
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Joined: Sep 2003
Posts: 1,688 Marlboro, NY, USA
Rick_Ehrenberg
top fuel
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top fuel
Joined: Sep 2003
Posts: 1,688
Marlboro, NY, USA
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General rule of thumb:
If it runs too hot <40 MPH, look at the fan/shroud.
>40 MPH, look elsewhere. Frequently missed: hood-to-yoke seals, lower air panels, etc.
Actual temp isn't really critical as long as it doesn't boil. Once that happens, you're dead meat - zero cooling.
Rick
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Re: 340 running hot (long)
[Re: ozz383]
#743209
07/08/10 09:20 AM
07/08/10 09:20 AM
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Joined: Apr 2009
Posts: 79 montreal, quebec, canada
jimmy71demon
member
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member
Joined: Apr 2009
Posts: 79
montreal, quebec, canada
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im having the same problem with my stroked 340. granted its warm out but it runs at 190 while cruzing, and easily goes up to 210 when stopped at a light. i didnt put a thermostat in it tho. thats the first thing im gonna try. im a little worried that the thermostat might restrict too much tho. so if it still runs hot with it, i think i will leave it in there but take the middle out of it. please keep us posted if u fix the problem and what u did. i will do the same!
p.s. i am running an electric fan with no thermostat on it (direct to the key) and a 3 pass rad
Im goin fast Mom!
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Re: 340 running hot (long)
[Re: ozz383]
#743211
07/08/10 11:31 AM
07/08/10 11:31 AM
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Joined: Jan 2003
Posts: 28,067 Irving, TX
feets
Senior Management
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Senior Management
Joined: Jan 2003
Posts: 28,067
Irving, TX
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Did you mean to say the radiator was cleaned up as well as the engine?
That was my problem. The new high flow water pump shoved all the good out of the engine and the radiator filtered the coolant for me. I took the radiator to get cleaned and it was more than 75% blocked.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: 340 running hot (long)
[Re: TJP]
#743212
07/08/10 11:37 AM
07/08/10 11:37 AM
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Joined: Feb 2005
Posts: 28,312 Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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Quote:
make sure there are no vacuum leaks and that the motor is not running lean, issues
If all of the above checks out then it may be time to start looking at the radiator itself
Richen it up, I'm sure it will help. Clutches on the fan go bad all the time. It will run hot when that happens, been there, done it more than once.
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Re: 340 running hot (long)
[Re: ozz383]
#743217
07/08/10 12:44 PM
07/08/10 12:44 PM
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Joined: Jan 2003
Posts: 27,468 So Cal
autoxcuda
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,468
So Cal
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Quote:
mine was great before now not so...ozz
The 340 in my Barracuda would never get hot. Actually most of the time when I cruised at higher speeds it would get cooler. Like if it was just cruising at 3600 rpm and went to 3800/3900 the gauge would go down. I've driven 1600 miles across country at 3800-4000 rpm.
Original pistons, original bore, hone job 70K miles ago. BUT when we did that hone job there was a bunch of scale in the coolant passages. We spend hours and hours with coat hangers and a vacuum removing and picking away scale. Filled up 3 baby jars of scale.
I have a Stock shroud, MP viscous fan, stock radiator, MP.455 cam, stock heads.
Motor was really getting worn in the last couple years (210K miles on OE bore). And was getting some big blow by. And it ate a #6 rod bearing about a month ago.
Only thing that was wierd with my cooling system was that when I put on a new 15 pound cap, it would run hotter. But when I ran my basically shot radiator cap it would run much cooler. Why is that??
When I was driving it across country year ago it had a radiator cap that tested out fine.
It ran this cool about and hour before the rod bearing let go!....
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Re: 340 running hot (long)
[Re: autoxcuda]
#743218
07/08/10 01:40 PM
07/08/10 01:40 PM
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Joined: Jan 2003
Posts: 28,067 Irving, TX
feets
Senior Management
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Senior Management
Joined: Jan 2003
Posts: 28,067
Irving, TX
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I can't believe you ran that poor thing at that thing of a speed for so long. It puked a rod because it wanted some time off.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind. - Stu Harmon
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Re: 340 running hot (long)
[Re: feets]
#743219
07/08/10 01:52 PM
07/08/10 01:52 PM
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Joined: Feb 2005
Posts: 28,312 Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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Quote:
I can't believe you ran that poor thing at that thing of a speed for so long. It puked a rod because it wanted some time off.
That is a unbelievable story there, Wow. I believe you, I bet it ate some gas along the way.
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Re: 340 running hot (long)
[Re: ozz383]
#743220
07/08/10 02:41 PM
07/08/10 02:41 PM
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Joined: Nov 2004
Posts: 1,708 S. Il. U.S.A.
5spdcuda
top fuel
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top fuel
Joined: Nov 2004
Posts: 1,708
S. Il. U.S.A.
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You have a lot of new parts. Obviously something is different from before. Old parts, it ran cool, fresh rebuild it runs hot. Clearly something has changed. As others have noted the fan really only affects low speed cooling. Since you say that the overheating only occurs after you've been on the road awhile I doubt that the fan is the problem. Head gasket seal SHOULDN'T be a problem, but a compression check can't hurt and besides it's a good idea to have a baseline on a fresh engine so that you have something to compare later checks to. Is there a spring in the lower radiator hose? If not, put one in. A new water pump shouldn't be a problem, but if all new parts were perfect there wouldn't be any need for warranties. The same goes for the thermostat. It's also possible as Feets noted that crud from the block could clog the new radiator. Did you have any head work done? It's unlikely, but still possible that if any work [ porting, hardened exhaust seats, milling, etc. ] was done that you now have exhaust gases getting into the cooling system. If you take a systematic approach sooner or later you will find the problem. Look at all the changes you made, since that is almost certainly where the problem lies. BTW you list S.Ill. for an address. That still covers a lot of territory, but if I can help in person or by phone PM me and I'll do what I can.
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