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340 running hot (long) #743202
07/07/10 10:50 PM
07/07/10 10:50 PM
Joined: Apr 2009
Posts: 162
southern illinois
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ozz383 Offline OP
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ok finally got the demon back together and running broke in cam and noticed it was getting a bit warmer tha i liked but between the big fan and playing with the timing we got through it. took it to get aligned (rebuilt front end and detailed while out)and then tried to get it dialed in .re-worked distributor am running 20 degree initial and about 35 total stock 70 intake and stock cast iron manifolds built back to stock specs with comp 274h cam as only major up grade over stock now it runs hot before i rebuilt it it barley would hit 160 (when i took it apart it had no thermostat in it)now sitting and idleing runs about 190 running down road it gets up to 210 or so and when idling up the gravel stretch to house it keeps climbing has a freshly recored stock 3 row radiator (has factory air but not working yet) it was full of rust so was block when i took it apart didnt think i would have a problem after every thing was cleaned up the only things that are diffrent than before is intake had spread bore and fan had a 7 blade direct drive put a 7 blade clutch type on instead any help will be greatly appreciated this car is about to get me down thanks in advance ozz

Re: 340 running hot (long) [Re: ozz383] #743203
07/07/10 11:19 PM
07/07/10 11:19 PM
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Posts: 1,043
Motown, Mi
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PAULS_340 Offline
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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
Re: 340 running hot (long) [Re: PAULS_340] #743204
07/07/10 11:24 PM
07/07/10 11:24 PM
Joined: Apr 2009
Posts: 162
southern illinois
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ozz383 Offline OP
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mine was great before now not so...ozz

Re: 340 running hot (long) [Re: ozz383] #743205
07/07/10 11:54 PM
07/07/10 11:54 PM
Joined: Jun 2010
Posts: 311
Colorado Springs, Colorado
Dartthunder340 Offline
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Colorado Springs, Colorado
Shot in the dark here, but what pound is the radiator cap?


Better get inside Ma. Looks like a storm's comin'.
Re: 340 running hot (long) [Re: Dartthunder340] #743206
07/08/10 12:54 AM
07/08/10 12:54 AM
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Posts: 6,906
IL, Aurora
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ademon Offline
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do you have a new fan clutch? a shroud? what t-stat?

Re: 340 running hot (long) [Re: ademon] #743207
07/08/10 06:57 AM
07/08/10 06:57 AM
Joined: Apr 2009
Posts: 162
southern illinois
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ozz383 Offline OP
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15lb cap. stock shroud and a tight feeling stock fan clutch 180 degree stat if i have time today im going to swap out fan setup for the direct drive to see if that helps ozz

Re: 340 running hot (long) [Re: ozz383] #743208
07/08/10 09:08 AM
07/08/10 09:08 AM
Joined: Sep 2003
Posts: 1,688
Marlboro, NY, USA
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Rick_Ehrenberg Offline
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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

Re: 340 running hot (long) [Re: ozz383] #743209
07/08/10 09:20 AM
07/08/10 09:20 AM
Joined: Apr 2009
Posts: 79
montreal, quebec, canada
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jimmy71demon Offline
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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!
Re: 340 running hot (long) [Re: jimmy71demon] #743210
07/08/10 10:20 AM
07/08/10 10:20 AM
Joined: Jan 2003
Posts: 15,197
Omaha Ne
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TJP Offline
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Omaha Ne
I will agree but restate
Idle/low speed heating is typically fan related. Be aware that Electric fans are ususally overated cfm wise and the performance of the fan is usually directly porportional to the price of it.
If it's getting warm above 30 to 40 MPH you have other issues as the fan should be out of the picture unless it is postioned as such that it is blocking the air flow.
I usually start with a digital thermocouple guage and probe inserted into the coolant as close to the thermostat as possible. This allows me to see exactly what is going on. I do not rely on infared meters as they can be inaccurate.
I have seen brand new gauges etc be off by as much as 50 degrees for various reasons
As previously mentioned if it's getting warm at low speed/idle and OK going down the road look at the fan
If it's getting warm going down the road
Make sure the lower hose is not collapsing,
Make sure your pulley ratios are correct,
Make sure the belt isn't slipping

Check for restrictions to the air flow

Check for air flow escaping by going around rather than through the radiator

Long shot but I have seen loose impellers on the water pump

make sure there are no vacuum leaks and that the motor is not running lean,
Timing being to far advanced at low speed or at higher speeds

block check the motor to make sure there is no internal issues

If all of the above checks out then it may be time to start looking at the radiator itself

Re: 340 running hot (long) [Re: ozz383] #743211
07/08/10 11:31 AM
07/08/10 11:31 AM
Joined: Jan 2003
Posts: 28,063
Irving, TX
feets Offline
Senior Management
feets  Offline
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Posts: 28,063
Irving, TX
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
Re: 340 running hot (long) [Re: TJP] #743212
07/08/10 11:37 AM
07/08/10 11:37 AM
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.

Re: 340 running hot (long) [Re: feets] #743213
07/08/10 11:38 AM
07/08/10 11:38 AM
Joined: Apr 2009
Posts: 79
montreal, quebec, canada
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jimmy71demon Offline
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Quote:

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.




that is a good idea. i never really thought of getting my rad cleaned. or even checked for that matter... thanks for the tip!


Im goin fast Mom!
Re: 340 running hot (long) [Re: jimmy71demon] #743214
07/08/10 11:42 AM
07/08/10 11:42 AM
Joined: Sep 2004
Posts: 6,906
IL, Aurora
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ademon Offline
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190 / 210 is not bad but if it keeps creeping higher than 210 in a short time at idle thats not good.

Re: 340 running hot (long) [Re: ademon] #743215
07/08/10 11:55 AM
07/08/10 11:55 AM
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I ran into a problem with my 340 and stock exhaust manifolds running hot. Put headers back on it was fine. Suggestion did you use a 8 blade pump? If not get one they will generally run the engine cooler. I currently run 190-195 in this 90degree heat nothing ar=t all with that when running a 190 stat. Suggestion also a heavy duty declutching drive fanfrom a dodge pickup will also help but if stuck with need for short shaft unit use one that will give you best idle cooling using a thermo spring on the drive

Re: 340 running hot (long) [Re: Paul_Fancsali] #743216
07/08/10 12:08 PM
07/08/10 12:08 PM
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Posts: 25,200
Upper Midwest
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MoparforLife Offline
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Upper Midwest
Try to back the timing down to 33 degrees and see what happens. I don't think that you will see a performance drop and may see a performance increase. I did, along with running cooler.

Re: 340 running hot (long) [Re: ozz383] #743217
07/08/10 12:44 PM
07/08/10 12:44 PM
Joined: Jan 2003
Posts: 27,444
So Cal
autoxcuda Offline
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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!....






Re: 340 running hot (long) [Re: autoxcuda] #743218
07/08/10 01:40 PM
07/08/10 01:40 PM
Joined: Jan 2003
Posts: 28,063
Irving, TX
feets Offline
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feets  Offline
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Irving, TX
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
Re: 340 running hot (long) [Re: feets] #743219
07/08/10 01:52 PM
07/08/10 01:52 PM
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.

Re: 340 running hot (long) [Re: ozz383] #743220
07/08/10 02:41 PM
07/08/10 02:41 PM
Joined: Nov 2004
Posts: 1,708
S. Il. U.S.A.
5spdcuda Offline
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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.

Re: 340 running hot (long) [Re: 5spdcuda] #743221
07/08/10 10:50 PM
07/08/10 10:50 PM
Joined: Apr 2009
Posts: 162
southern illinois
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ozz383 Offline OP
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ok internet has been down all day so now i can ck in.i am going to try to answer as many questions as i can remember. rad. was found to be plugged and full of rust when removed so i had it checked and they found it to be rotted so they recored it with a 3 row as it was from factory. block was boiled and shot peened and then cked over very closley for remaining rust block was full upon teardown. 2 freeze plugs were rusted out and it did not leak coolant beacuse it was so plugged up. compression is steady at about 180 cranking psi but rings are probley not completly seated yet only has about 50 to 60 miles on it removed fan and clutch assembly today and put the fan back on it that was there when i got it (7 blade direct drive only markings on it is a stamp that says 58??) ran it it ran cooler but it was also cooler out. cked next to sender with ir heat gun and only showed 182 degrees while gauge said 215. im going to remove heater core hose nipple and install a mechanical guage and see what it shows. it has a autometer electric guage in it now. have to work all weekend. wife is taking it to the church car show this weekend, after that i will start trying to figure this out. next on list after new guage is drill out thermostat for more flow i"ll keep you all posted thanks again for the help ozz

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