trippled
NAXJA Forum User
- Location
- colorado springs, co
Good deal! Although it sounds like you need fans anyways, keep in mind they do very little if anything at higher speeds. I'm not sure how fast you're going though.
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Overheating only on a load, heavy mods
- Thread starter 1989AMCXJ
- Start date
- Location
- Torrance, CA
Get rid of the fans, they don't help at all. No electric fan that will fit in the space will pull as much as an OEM electric fan. Search for the ZJ fan clutch and use that plus the OEM fan and an OEM electric fan.
- Location
- Golden, CO
What is your compression ratio, what grade fuel?
- Location
- Rainy side of Washington
Agreed.
Also, are you sure your trans isn't slipping a bit? I saw no mention of that. I had bad overheating problems in my 96 XJ just before the transmission blew, and they were gone afterward when I installed the new trans. Don't underestimate how much heat a slipping trans can dump into your radiator.
I am leery of the "coolant flowing too fast for effective cooling" argument as an engineer because it doesn't make logical sense to me, but I haven't done the test I need to on my 88 MJ yet so I will not argue that... yet. Pretty sure its thermostat is currently stuck open, so I am going to remove it and see what happens, then put in a stant 195 and compare.
Not necessarily. I replaced the mech fan in my jeep with a 14" spal fan. it worked great going slow/crawling wouldn't even get off 195. Going down the highway was a different story. Flat ground 65mpg 80 degrees out. 215 with the fans running. 225 with out and would probably climb higher that's just where I backed off and let it cool down. Any grade and it would instantly climb even with the fans running.
Swapped back to the mech fan and runs 195-200 every where except climbing grades where it will get up to 210-215.
The mech fan DOES pull air at highway speeds.
OP put the mech back on with a new clutch
The coolant flowing too fast to transfer heat is completely false.
The t-stat back pressure may prevent pump cavitation but nothing is needed in addition to a the factory t-stat as proven by millions of xj's.
I'm sure I can find 100 more sources like this. Too fast to transfer doesn't make any sense. It's a continuous flow, faster will just max out the transfer ability of the rad or the engine until you're actually generating more heat with molecules but that's a long way off to be causing trouble.
http://stewartcomponents.com/index.php?route=information/information&information_id=11
http://stewartcomponents.com/index.php?route=information/information&information_id=11
Green XJ Jeep
NAXJA Forum User
- Location
- Spanaway Wa
Is the afr measured at an idle or under a load?
You never mention if you did anything with the injectors and with the mods it sounds like a case of to much air going in and not enough fuel.
clydefrog
NAXJA Forum User
- Location
- Northern California
Hows your a/c condenser look? Assuming your running one, overheat under load most commonly could be from lack of airflow. I had a condenser that was full of bugs (didn't even look super bad) and I had the exact problem you are experiencing....surprised it hasn't been mentioned yet. I changed mine out (after pulling out my hair and changing EVERYTHING else and problem was solved). If your condenser looks good or if you don't even have one then ignore this post, otherwise definitely something to look into.
TRCM
NAXJA Forum User
- Location
- Newport News,VA
It's not as much of 'flowing too fast to transfer heat', as it is flowing to fast to transfer enough heat.
Like I said a few posts up.........what cools you off more when you are hot......running quickly thru an air conditioned room, or walking slowly thru it ??
And I'm not sure, but the restriction thing is in place of a t-stat normally....at least on the race engines I have dealt with. And they were mainly to keep the pump from cavitating at the high rpm the engines see.
I agree, in a non race engine, a stock style t-stat should be all ya need.
However you want to reword it the answer is the same it's a myth.
The transfer of heat at the radiator will be maxed out by increased flow rate. Whether all of the heat leaves is irrelevant the max amount the radiator can sink will continue to flow out of the cooling system/engine
Your analogy doesn't apply, our bodies generate a massive mount of heat for movement compared to a pump generating little heat.
So yeah an air conditioned room with wind blowing 20mph by you will cool you alot faster than idle air, See Windchill.
The pump cavitation has been misrepresented as "flowing too fast to transfer heat" by mechanics that didn't know any better when they pulled the tstat expecting better results.
Corelation is not causation
The transfer of heat at the radiator will be maxed out by increased flow rate. Whether all of the heat leaves is irrelevant the max amount the radiator can sink will continue to flow out of the cooling system/engine
Your analogy doesn't apply, our bodies generate a massive mount of heat for movement compared to a pump generating little heat.
So yeah an air conditioned room with wind blowing 20mph by you will cool you alot faster than idle air, See Windchill.
The pump cavitation has been misrepresented as "flowing too fast to transfer heat" by mechanics that didn't know any better when they pulled the tstat expecting better results.
Corelation is not causation
I just wanna point out something about fans. Just because you're moving fast, doesn't mean your fans don't matter. A fan that is turned off, or just windmilling creates a HUGE amount of drag. I fly small planes, and anyone else who has could tell you just how much drag a windmilling prop has. There's a reason twin engine planes have feathering props, it's because a prop that is stopped creates far less drag than one that is spinning. When you pull the throttle back from 1/4 to fully closed you can feel the plane slow down due to this drag. They say it's almost as bad as having a flat plate the diameter of the prop out there. In the case of a radiator cooling fan if you're driving 65mph through the air with the fan turned off, there's every possibility that your fan is creating so much drag that it's actually blocking flow, and if your fan can't push enough air through when it's turned on you're also still losing flow. This is why the 3 electric fan setup sucks.
If your 3 fans make 2000cfm each (and it's doubtful that any 10" fan does) you will basically never get more than 6000cfm through your radiator regardless of speed. The fans are the limiting factor thanks to drag. The stock clutch fan pulls quite a bit more than that, plus the addition of the stock electric. This is why sometimes you can cool a motor with the electrics going slow or with a light load, but not when moving fast with a higher load, even though simple logic says that moving fast should give enough air flow. In reality you'd need to have NO fans or shroud on the back side to make use of that speed induced airflow, but then you'd have problems at slow speeds.
If your 3 fans make 2000cfm each (and it's doubtful that any 10" fan does) you will basically never get more than 6000cfm through your radiator regardless of speed. The fans are the limiting factor thanks to drag. The stock clutch fan pulls quite a bit more than that, plus the addition of the stock electric. This is why sometimes you can cool a motor with the electrics going slow or with a light load, but not when moving fast with a higher load, even though simple logic says that moving fast should give enough air flow. In reality you'd need to have NO fans or shroud on the back side to make use of that speed induced airflow, but then you'd have problems at slow speeds.
- Location
- Hammertown, USA
I hate seeing these threads come up over and over again.
I have thrown somewhere around $4000 in the trash over the last 5 years playing with cooling system upgrades and getting somewhat scientific about it at times.
At the end of the day, I ended up with an upgraded radiator and stock everything else for the best cooling.
Maybe I'm just not hard enough on my jeep to justify more?
I have thrown somewhere around $4000 in the trash over the last 5 years playing with cooling system upgrades and getting somewhat scientific about it at times.
At the end of the day, I ended up with an upgraded radiator and stock everything else for the best cooling.
Maybe I'm just not hard enough on my jeep to justify more?
- Location
- REDLANDS, CA. (SoCal)
TRCM
NAXJA Forum User
- Location
- Newport News,VA
Myth or not...I have proven it to be so several times in real life in my vehicles. It's not the 'flow is too fast to cool' it's the 'flow is too fast to cool enough'....under the current conditions...which means flow thru the radiator on both sides of the tubes.
Real life story:
I once put a dual pass radiator on an old dodge truck I had along with a high flow rate pump....worked ok, but not great. Put the stock single pass radiator back on as a test to see what happened, & it worked much better. With the dual pass, a given volume of water had to pass thru twice the length of tubing in the radiator as it did in the single pass one....and 2x the distance in the same amount of time means twice as fast. The single pass radiator with the lower flowrate cooled better to the tune of 10-12 degrees lower engine temps @ 60 mph...all other components stayed the same, and the temp outside went up, not down.
1) the flow rate of the coolant will never max out the heat transfer rate....you can always flow faster
2) the heat transfer rate from the coolant to the radiator material is limited by the specific heat capacity of the metal or plastic the radiator is made of and the temperature difference, not how fast the fluid is moving thru it
3) no matter how fast or how much the coolant transfers to the material of the radiator, the heat transferred will be limited by the flow rate of the cooling medium thru the radiator, the temperature difference of the cooling medium & radiator materials, as well as the specific heat capacity of the material the radiator is made of.....(can't add heat if it's already as hot as it's gonna get.....must take it away first)
4) My analogy works just fine........never mentioned 20 mph or idle air....just said if you walk thru vs run thru....one makes you feel colder/cooler, and it is not windchill, it is the simple fact that you spent more time in a cool environment, so more time for heat to transfer.
You can also change words how you want, but in doing so, you changed what I said.
Yes, our bodies do produce a lot of heat (relatively) to move, but the point was, you are hot from being outside and being exposed to the radiating heat from the sun......the amount of heat produced when moving is negligible to the heat that makes you feel hot....unless you've been running a marathon. Did you forget to counter that you are also cooler cuz you ain't in the sun no more ??
5) pump cavitation...I never said any of that crap....I simply mentioned cavitation ......which is something that occurs when the pressure at the pump eye/suction drops low enough for air/vapor pockets/bubbles to form......and we all know air bubbles in the coolant don't cool worth a darn in 99% of the situations out there. With no restriction, there is no back pressure, and with no back pressure, the suction pressure of the pump drops, and can lead to cavitation.
If it gets bad enough, those air bubbles/vapor pockets can also implode/collapse later on in the system when pressure goes back up, and the sudden pressure surge from this can severely damage components...even cast iron blocks.
As has been said many times now......the best working system is one that uses stock components and a stock or high capacity radiator. Almost every time I have read a post on here about cooling issues, it's from someone trying to make it work better with fancy aftermarket parts, but they are failing at it cuz they are still getting too hot or overheating.
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TRCM
NAXJA Forum User
- Location
- Newport News,VA
No comment on my real life example.......................
I'll use my original post, not your shortened versions.......
1) the flow rate of the coolant will never max out the heat transfer rate....you can always flow faster (missing smiley for humor effect..sorry)
2) the heat transfer rate from the coolant to the radiator material is limited by the specific heat capacity of the metal or plastic the radiator is made of and the temperature difference, not how fast the fluid is moving thru it
Well, they aren't contradictory, the flow rate of the coolant will not max out the heat transfer rate....the temp difference between the inner & outer wall of the material heat is being transferred across and the thickness of that material, combined with the specific heat capacity of the material is what determines the max heat transfer rate...flow doesn't..which is exactly what I said. Now, flow does have a bearing on how much heat is transferred
3) no matter how fast or how much the coolant transfers to the material of the radiator, the heat transferred will be limited by the flow rate of the cooling medium thru the radiator, the temperature difference of the cooling medium & radiator materials, as well as the specific heat capacity of the material the radiator is made of.....(can't add heat if it's already as hot as it's gonna get.....must take it away first)
not so sure why you 'lol''d this one, as it is spot one......
cooling medium is the airflow, not coolant flow
the temp difference between the radiator materials & the air, as well as airflow, determine how fast the heat transfers
I say materials, as the coolant isn't in contact with the air, and the materials will insulate to a small degree
4) My analogy works just fine........never mentioned 20 mph or idle air....just said if you walk thru vs run thru....one makes you feel colder/cooler, and it is not windchill, it is the simple fact that you spent more time in a cool environment, so more time for heat to transfer.
Ok, not sure where the continous flow of water thing came from, as the problem here is how to cool the water off using the air flow thru the radiator...not how to cool the block off using water flow...apparently that is already figured out since the water is hot.
And the person would be the heat carrying item, and the room temp or cool air in the room would be the cooling medium. No one said anything about air flow......I said you walk thru vs run thru...no airflow mentioned, just a cool air conditioned room
Yes, our bodies do produce a lot of heat (relatively) to move, but the point was, you are hot from being outside and being exposed to the radiating heat from the sun......the amount of heat produced when moving is negligible to the heat that makes you feel hot....unless you've been running a marathon. Did you forget to counter that you are also cooler cuz you ain't in the sun no more ??
Been there, done that...every day in fact. In my analogy, I said walk or run thru a room, and if you develop enough heat in your body running thru a normal sized room, then you must be fatter than me, and I ain't little. Anyway....the heat from the sun you feel on your person is much more than the heat produced from you moving, because that heat is small, but if you continually produce it (like in a marathon), it builds up faster than you can get rid of it, especially if you are out in the heat from the sun. It is just easier to get out of the heat from the sun and cool off quickly as compared to cooling off from exertion.
But hey, you don't like my analogy, so again, who cares ?
5) pump cavitation...I never said any of that crap
You didn't no, but I did. It's the real reason behind increased temps at faster speeds miss attributed as too fast to transfer "enough" heat.
Corelation is not causation.
Well, it IS one of the causes of increased temps at faster speeds, but not the only one.
By your logic, the speed of the hot fluid is irrelevant to the heat transfer rate when it passes thru a radiator....since there is no such thing as too fast right ?? The same amount of cooling will be seen at 5 gpm as 50 gpm ??
If you start welding your frame...does the whole frame heat up at once ?? no, it takes time......same with anything else...it takes time to transfer the heat....so, more time = more heat transferred. A lower flow rate will give the radiator more time to transfer the maximum amount of heat to the air and thus cool things off better.
I can agree...Correlation is not Causation.
:worship:
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Because anecdotes are anecdotal.
- Location
- Rainy side of Washington
TRCM, your huge missed point in your assertion that "it flows faster and doesn't have as much time to cool off in the radiator" is that it also flows faster in the engine and doesn't have as much time (per coolant "lap") to pick up heat there. It just does more laps in the same time to make up for that, because that's how physics works. Sorry.
Some engines have external thermostat housings with a bypass hose back to the WP from the hot side of the stat so that there is still coolant flow over it when it is closed to keep the thermostat at the same temp as the water jackets so it can do its job. Good examples include the BMW M10 and the GM 2.2L OHV in the Cavalier. If the system is set up this way, removing the stat can in certain cases result in increased flow through the bypass and less through the radiator, resulting in overheating. However this does NOT apply to the 4.0 and a 4.0 will not overheat if you remove the stat, sorry.
External thermostats with bypass hoses and coolant cavitation caused by extremely high flow can cause overheating. Mere high flow from a removed thermostat will not unless it results in cavitation.
Like I said, I will be testing this soon. Feel free to argue all you want, I've said my piece, I agree with AIBandit, and will be happy to eat my words if my test proves me wrong.
Edit: also, your example of walking vs running is spurious for two reasons. It is an open system not a closed one (you are passing through air you will never see again, thus its exit temperature is irrelevant) and you expend energy increasing the flowrate. Both affect the results.
Some engines have external thermostat housings with a bypass hose back to the WP from the hot side of the stat so that there is still coolant flow over it when it is closed to keep the thermostat at the same temp as the water jackets so it can do its job. Good examples include the BMW M10 and the GM 2.2L OHV in the Cavalier. If the system is set up this way, removing the stat can in certain cases result in increased flow through the bypass and less through the radiator, resulting in overheating. However this does NOT apply to the 4.0 and a 4.0 will not overheat if you remove the stat, sorry.
External thermostats with bypass hoses and coolant cavitation caused by extremely high flow can cause overheating. Mere high flow from a removed thermostat will not unless it results in cavitation.
Like I said, I will be testing this soon. Feel free to argue all you want, I've said my piece, I agree with AIBandit, and will be happy to eat my words if my test proves me wrong.
Edit: also, your example of walking vs running is spurious for two reasons. It is an open system not a closed one (you are passing through air you will never see again, thus its exit temperature is irrelevant) and you expend energy increasing the flowrate. Both affect the results.