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  #1  
Old 06-11-2002, 10:49 AM
Dan G Dan G is offline
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Ok, it's been a while since I've been on, so I have accumulated my share of Jeep woes.

I installed a plow in early January at my brother's house 75 miles from home. On the way home, big yellow plow pushed all the air away from DSPO's 2 core radiator (YES, on a 360) and caused me to overheat 260+ deg F. Brother was kind enough to loan me trailer, buggy lugged plow into trailer (of course during the ONLY snow storm we had all year), and managed to make it home.

I purchased a new 4 core radiator and installed it, and what the heck took out the thermostat for good measure. Since that time, I've done my usual Home Depot runs without so much as a blip towards hot on the temp gauge.

Decided that since 'Running Hippo' is 'running sooo well' that I should take another long trip.

WELL, tranny won't go into third until I hit 60mph, used to happen at 40mph. 'RH' is still pushing lots o' heat, the temp gauge is telling me 240. Stop and go traffic makes gauge crawl towards 250.

Prequalifiers... engine is at 208K miles without a rebuild. I am at least 4th owner. Timing chain probably needs to be done desperately, rebuild needed in near future.

Question 1: Is overheating due to timing chain?

Question 2: Is tranny problem due to vacuum modulator (TF727)

Question 3: Does anyone want to buy a slightly rusted FSJ with a plow? She's dark blue with the 'light cordovan' interior...
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  #2  
Old 06-11-2002, 10:59 AM
River Beast River Beast is offline
 
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Check your fan clutch... sounds like it's not pulling the air through the radiator for cooling...also check the weep hole on the bottom of the snout of the waterpump for weepage. Your pump can be on it's way out as well....

Have you tried backflushing the system? You could have some crud built up in the water jackets in the block.

Can't help you on the 727.. I have a TH400..sorry

Don't sell it just because of this...get it fixed and be a proud FSJer!!!
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Old 06-11-2002, 06:15 PM
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#1 put a thermostat back in it (factory temp one) I think they were 195 degress,that will let the water sit in the rad long enough to cool off and let the clutch fan work proprly.
#2 tf727's don't have vac mods they use a cable to the carb for shift points.
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  #4  
Old 06-11-2002, 08:21 PM
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How are your other shift points? If 1st & 2nd still shift at the previous points then you may have an internal problem with your tranny. What about manually shifting from 2nd to 3rd? Any probs there? If all of the shift points are now at higher mph/rpm, then you can adjust the shift linkage (looks like a Chebby kick-down linkage below your throttle linkage on the carb.). Tech section has a write-up on that procedure. Very important to set this shift linkage correctly or else you get much tranny clutch wear and much excess heat produced due to an over-revved motor.
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Old 06-12-2002, 12:03 AM
River Beast River Beast is offline
 
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OOOPS!! I thought you meant you 'changed' out the the thermostat....yeah you need one for city driving for sure...
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  #6  
Old 06-12-2002, 02:40 AM
J20fan J20fan is offline
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I change out to 165* thermostat for the summer months. This keeps my engine temp at an excellent level in higher ambient temperatures. I also flush the system with a cooling system flush that removes scale etc. from the block.
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  #7  
Old 06-13-2002, 10:57 AM
Dan G Dan G is offline
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"Very important to set this shift linkage correctly or else you get much tranny clutch wear and much excess heat produced due to an over-revved motor."

Thanks Monster Mash!! Will do!

Also, will reinstall t-stat, though I might make a slight mod to it. Recently have been reading about adding a 1/8" hole to the flange of the t-stat to allow bypass if t-stat ever gets stuck.

Any thoughts??
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  #8  
Old 06-14-2002, 12:12 PM
1BADJP 1BADJP is offline
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Are you running a trans cooler or just the one in the radiator??
Install a HD trans cooler and run it through the radiator also.
try changing your trans fluid and filter--probably cooked fluid when overheated engine.
definitly check your fan clutch
You may need to install electric fan when plow is on to help cool radiator.
200,000 miles shouldn't be a problem if engine flow is good, look at flow in radiator while engine is running to see if it is flowing at all.
Do you know anyone with a laser temp gun??? they work real well and can pinpoint alot of system problems.
I wouldn't drill any holes in housing---if Jeep wanted one they would have put one!!!
GOOD LUCK
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  #9  
Old 08-28-2002, 03:10 PM
Dan G Dan G is offline
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Ok, reviving my old topic here...

1. I lubricated the TV linkage and readjusted it, tranny still operating poorly, won't go into 3rd until 60 and goes back in to 2nd shortly below 60.

2. 1BADJP, not drill hole in t-stat housing, drill hole in t-stat flange to allow a bit of bypass if element gets stuck. Has anyone done this?

3. 1BADJP, been looking for a reason to buy one of those laser temp guns. HVAC engineer by trade, maybe I can write it off as a 'work tool'!?!

4. Will changing out the valve body, fluid and filter cure my problem or am I in for a complete tranny rebuild.

5. If complete tranny rebuild, what's the going rate for a rebuild with the B&M manual shift valve body (2nd means 2nd and 1st means 1st) and HD clutches??
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  #10  
Old 08-28-2002, 04:24 PM
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as for the trans shift point problem on the 727 there is a spring at the back of the intake that keeps tension on the linkage if the spring is gone/broken it will make the 3rd gear shift real late also the bushing in the kick down linkage at the bellhousing that holds the linkage cross shaft crack and fall out with age as for the over heat problem i would look at the fan clutch the lazer temp guns are cool as for the b&m man shift body and kevlar clutches and viton seals it runs about $600.00 for their kit
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  #11  
Old 08-28-2002, 04:31 PM
ibnfe ibnfe is offline
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In my experiences on trannies, usually changing out the valve body with new will usually reveal all the other pending problems in the tranny. If you change the valve body and don't rebuild the tranny, you will probably need to within a short time. My 727 made it 'til 230,000 miles before everything started going south. As far as the rebuild goes, you can get all the consumable stuff for less than $250.00, and that includes a new converter. I do all of my own maintenance, so I can't help on how much it would cost to have someone else do it. Here's what the 727 tech manual says are probable causes for your delayed upshift: throttle linkage needs adjustment, kickdown band out of adjustment/worn/broke, worn seal rings, reaction shaft support rings worn, worn front clutch, governor problem. The first two are what I would concentate on first since they are easy and will avoid the rebuild if they work. Check/adjust your throttle linkage and the front band. If those and a fluid/filter change don't fix your problem, then it is internal somewhere.
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  #12  
Old 08-28-2002, 05:28 PM
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Steven79 brought up the theory that:

[#1 put a thermostat back in it (factory temp one) I think they were 195 degress, that will let the water sit in the rad long enough to cool off and let the clutch fan work properly.]

*****************************************

There was a post a while back on the LT1edit list regarding the issue of flow rate through the radiator and I thought some on this list might be interested:

----------------------

According to Newton's law of forced convection, the amount of heat transferred can be represented as this:

Q=hA(Tw-Tr)

Where:
Q is the amount of heat in calories or BTM's or whatever unit you like.
h is the heat transfer coefficient for the system
A is the area of the surface where the heat transfer takes place and (Tw-Tr) is the difference in temperature between the coolant and the radiator (or the engine), i.e. delta T.

Nowhere does it mention the speed of convection. Because we're talking about identical setups except for flow, all the variables will be identical except for coolant temp. ***All that matters in determining how much heat is transferred is delta T, the difference in temperature between the coolant and the radiator.***

Let's look at two scenarios:

Scenario 1: 10 GPM coolant flow
Coolant temp coming out of the engine: 180 degrees
Ambient air temp: 100 degrees
Coolant temp as it comes out of the radiator: 120 degrees
Average delta T across radiator: 50 degrees

Scenario 2: 30 GPM coolant flow. Three times the flow, so the coolant is in the radiator 1/3 as long and loses only 1/3 as much temp per gallon:
Coolant temp coming out of the engine: 180 degrees
Ambient air temp: 100 degrees
Coolant temp as it comes out of the radiator: 160 degrees
Average delta T across radiator: 70 degrees

An average 70 degree difference vs. a 50 degree difference works out to 40% better heat transfer for the 30 gpm system, even though the drop in temp across the radiator is three times less than the 10 gpm system. Since the engine is going to be producing the same amount of waste heat in both cases, the delta T's for both systems must be the same. Therefore, for the second system, the coolant values would have to be 160 coming out of the engine and 140 coming out of the radiator. I realize it won't be exactly those values, but I'm not up to differential equations right now.

So despite the fact that the temperature drop across the radiator is less in the faster flowing system, you have 40% greater heat capacity for racing and on average your coolant temps will be lower. An added bonus is that because the coolant temp inside the engine is lower, you will be less prone to pinging and the computer will run more timing.

Now, why do you have to put a restrictor in the cooling system of an older smallblock to run without a thermostat? Well, it actually has nothing to do with thermodynamics, at least not directly. You can reference the faq at www.stewartcomponents.com if you want to verify what I'm saying, but the short of it is this: The restrictor isn't there to regulate flow, it's there to regulate pressure. The radiator is on the high side of the pump on older systems, and as the pump pressure climbs with increased flow, it will eventually push the safety cap open, even though it's not boiling over, causing a gradual loss of coolant and eventual overheating when the pump starts cavitating. That's all. The LT1's system has been re-designed so the radiator is on the low side of the system and not subject to high pressure. The only reason you even need a restrictor is to hold the gasket in place for the water neck.

Sorry if I rubbed anyone the wrong way, but you've got to nip disinformation in the bud before it becomes an urban legend.

Stonebreaker
-------------------------------------

What's this mean as far as FSJ's are concerned? It appears the thermostat not only regulates the engine temp, it also helps regulate the pressure the radiator see at higher rpms. It's not there to slow down the flow through the radiator although the stock thermostat certainly is a significant restriction. I use a high flow style thermostat that is available at most speed shops and through PAW. It is available in 160, 180 and 195 temperatures. They all have a couple of small bypass holes drilled in the housing to allow a small amount of heated coolant to flow through the thermostat so it will open sooner as the engine reaches the setpoint temp. When they are fully open they allow a significantly larger volume of coolant to flow through the system to the radiator than the stock thermostat. This type thermostat is also of a higher quality and less prone to failure than the stock ones. Hope this was of value to the list.

[ August 28, 2002, 11:29 PM: Message edited by: Wesdog ]
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  #13  
Old 08-29-2002, 02:03 AM
Al Johnson Al Johnson is offline
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Wesdog, I just love it when the math confirms my gut feeling on how stuff works. Never made sense to me to slow the flow of coolant to make it cool better.
Thanks for showing us the facts!
Al
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Old 08-29-2002, 02:44 AM
krob725 krob725 is offline
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You don't need to drill a bypass hole because it has a bypass hose already there.

krob725
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  #15  
Old 08-29-2002, 04:13 AM
fredws fredws is offline
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Quote:
Scenario 1: 10 GPM coolant flow
Coolant temp coming out of the engine: 180 degrees
Ambient air temp: 100 degrees
Coolant temp as it comes out of the radiator: 120 degrees
Average delta T across radiator: 50 degrees

Scenario 2: 30 GPM coolant flow. Three times the flow, so the coolant is in the radiator 1/3 as long and loses only 1/3 as much temp per gallon:
Coolant temp coming out of the engine: 180 degrees
Ambient air temp: 100 degrees
Coolant temp as it comes out of the radiator: 160 degrees
Average delta T across radiator: 70 degrees

An average 70 degree difference vs. a 50 degree difference works out to 40% better heat transfer for the 30 gpm system, even though the drop in temp across the radiator is three times less than the 10 gpm system. Since the engine is going to be producing the same amount of waste heat in both cases, the delta T's for both systems must be the same. Therefore, for the second system, the coolant values would have to be 160 coming out of the engine and 140 coming out of the radiator. I realize it won't be exactly those values, but I'm not up to differential equations right now.
Well, hate to bust Stonebreakers bubble, but. . . .

The heat transfer given in BTU/hr would be:

Q=M*Cp*deltaT

where Q is the heat transfer in BTU/hr
M is the flowrate, in GPM
Cp is 500 for water, of course with antifreeze it will be a bit different, but won't matter here as we are just compairing the two.
and of course deltaT is the difference in the entering and leaving fluild temp.

anyway, if you plug all that in for each case:

10*500*(180-120)=300,000 BTU/hr

30*500*(180-160)=300,000 BTU/hr

No difference.
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  #16  
Old 08-29-2002, 05:47 AM
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Fredws, interesting info. I see that you list your occupation as a research engineer so I assume you have the background to know what you are talking about. I am not a degreed engineer but I read a lot and know a little about a lot of different fields. The bottom line appears the same to me regarding the need to slow down the flow through the system - it is not a valid concern at the flow rates involved. There is a problem of having to low of a flowrate and I assume there are upper flowrate limits that are constrained by allowable system pressure and the restriction to flow. The fluid used and its ability to absorb and release thermal energy as you pointed out is part of the equation. Thanks for taking the time to respond, I may have some fun with the data you provided. Where is the formula from? The guy who wrote that post I included knows his stuff. I know there is always more than one way to analyze this sort of situation and there are a lot of variables but my intuition tells me that the higher flow would have a higher efficiency and provide better heat transfer. I believe the pressure drop in the radiator also has a significant cooling effect so a high flow system needs a highflow/low restriction radiator to work properly. Ok enough of this for now. I'm going to do some brushing up on this to clear up some questions I have.
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  #17  
Old 08-29-2002, 06:34 AM
fredws fredws is offline
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Wesdog, the equation is derived from the Bernoulli equation, of course modified to gpm instead of velocity, simple conservation of energy. But this of course is measuring the amount of energy removed from the fluid by the radiator. It is not the job of the thermostat to control the amount of heat rejected in the radiator, but instead to maintain a desired operating temperature in the engine.

but . . . back to the problem, no pun intended [img]smile.gif[/img] , I would guess that he is not getting flow, since the radiator is new and there is no thermostat, I would think that there must be a hose collapsing somewhere or like RB said, block needs to be backflushed. The backflushing is a good idea either way, I do mine once a year just for good measure!
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  #18  
Old 08-29-2002, 06:34 AM
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Quote:
Originally posted by Wesdog:
I believe the pressure drop in the radiator also has a significant cooling effect so a high flow system needs a highflow/low restriction radiator to work properly.
If you are suggesting that the pressure drop helps cooling in the same way an A/C unit cools by dropping the pressure of the coolant in the condensor, then you believe incorrectly...the pressure in a automotive cooling system is there for one purpose...to keep the coolant from boiling...

BTW, on a separate note, let me throw out a little more A/C tech on here that may help to explain why a faster flowing coolant can cool more efficiently than a slower flowing one....
In a residential a/c system (for example) if the temperature difference (known as Delta T) between the incoming air and the outgoing air at the compressor unit is too high (ie, the air is getting heated up a lot) you would think at first that the unit was performing well and that it was really transferring a lot of heat to the air. This thought is incorrect, a high delta T means only one thing...the air flow is restricted....the reason an air flow restriction raises the delta T is because what little air that is going through the fins is moving slower and hence, is getting hotter. The problem is that, operating in this manner, the system is inefficient and will not provide enough cooling. Why? Because a little air that is super heated is not as effective as a lot of air that is only slightly heated...
its the same concept in the coolant system of a jeep...a little bit of super heated coolant passing through the fins will not take away as much heat from the engine as a higher volume of fluid that moves faster (and hence carries less heat per gallon)

So it all makes sense in my mind...did I explain that well enough that it makes sense in yours? [img]tongue.gif[/img]
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Old 08-29-2002, 06:46 AM
fredws fredws is offline
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Jode, you got it! You have to look at the energy, not the temperature, there is a difference. So, it either does not have enough air flow across, or not enough coolant flow through.
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Old 08-29-2002, 10:14 AM
Dan G Dan G is offline
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ok, enough of heat transfer

Fredws, you prove correctly that the BTUs removed is identical with different flows, but what everyone seems to be ignoring is the upper limit of the delta T.

Obviously, if I was at 260 deg F (assuming Jeep gauge and interpolation are correct), then I'm concerned about my returning water temperature almost more than I am about the heat rejected, because at too high a temp, the engine and tranny cook
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