Overheating and already replaced all the usual suspects

I think I'll flush once more and put a factory tstat back in just to be on the safe side. The water flow concern seems reasonable although obviously not the cause of any harm. It has to go in at some point anyways, I'll just give it the stove top hot water test.

By the way, has anyone had good luck with a champion radiator? I got in touch with radiator express and my impression thus far is that they are not a decent company to work with. And before anyone says it, I know... I know... It's my fault. My point isn't to bitch or cry about it. I'm just saying
 
Qban said:
I think I'll flush once more and put a factory tstat back in just to be on the safe side. The water flow concern seems reasonable although obviously not the cause of any harm. It has to go in at some point anyways, I'll just give it the stove top hot water test.

By the way, has anyone had good luck with a champion radiator? I got in touch with radiator express and my impression thus far is that they are not a decent company to work with. And before anyone says it, I know... I know... It's my fault. My point isn't to bitch or cry about it. I'm just saying
Click to expand...

Stant makes a premium thermostat, which will also fail open as opposed to closed. The 195 degree one I use is part number 45359. Rock Auto sells them for $4. Also, I've heard that drilling a 1/8" hole in the housing and orienting the hole to the top of thermostat when installing can help in bleeding the air out of the system.

As far as running without a thermostat, and whether the water flows too fast or not, all I can say in my personal experience, with recorded temperature readings at T-stat, upper and lower hose, and side and middle radiator measurements, vs. having a thermostat installed, I found without a thermostat significantly less temperature drop across the radiator. This also resulted in a higher overall temperature throughout the system. To each their own.

David Bricker / SYR
 
David_Bricker said:
.......I've heard that drilling a 1/8" hole in the housing and orienting the hole to the top of thermostat when installing can help in bleeding the air out of the system........
Click to expand...
I have done this for years, on all my vehicles.
Some thermostats come with this hole already
drilled, but if not I drill it...
 
x2.
I've also heard of people using a restrictor in the cooling system to increase radiator dwell time - or the time that the coolant is in the radiator shedding heat - with positive results. Which seems to contradict the "can't flow too fast" thing.
 
Also the difference as I understand between the Jeep closed and open loop cooling systems has to do with handling the pressure and fluid overflow including reservoirs. How does that affect flow?

There is definitely a coolant flow speed that is optimal for a given setup. A variable speed electric pump and 2 thermocouples could show at what gpm the radiator has the largest temperature drop.
 
Ok. I read the article you referenced, looked it up in my Thermo text book, and did a little online research regarding the cooling coefficient alpha.

My response is for the geeks. For the rest of the population, just go with the higher flow rate is always better in a vehicle application.

The reason this is mostly true is because the faster the coolant moves through the radiator, the more the area consisting of a relatively high temperature difference (delta T) is spread across the physical area of the radiator. As a function of time, this larger spread of higher delta T will transfer much more heat energy to the system surroundings.

I disagree with the use of the term "impossible", however in the spirit of speaking in applications and not absolutes, I can pretty much agree with it. Absolutely speaking, coolant could travel so fast through the heat exchanger that there just wasn't any time for the fluid molecules to really dissipate much heat. As far as applications in an automobile go, you will never have to worry about it, since the pumps used are not capable of flowing the coolant that fast.

I did NOT like the use of the quenched rod analogy as applied to a radiator. It does illustrate the relationship of heat loss to delta T well, however.

If any other geeks wanted to explore this further, I suggest picking up a Thermo textbook. :) Here is an excerpt from mine.



Thanks for the accurate post, Rockclimber. Please excuse my need for quantification and detailed understanding. I find it very difficult to take anything at face value anymore. You understand. :)
 
Tony_SS said:
So the whole 'the coolant's moving too fast' is purely a myth.
Click to expand...


Here is where I disagree with that statement.

My previous career in the Virgin Islands was a power boat mechanic trained in Mercury and MerCruiser products. There have been countless times when an otherwise perfectly running inboard or stern drive engine would over heat even though it have more than enough water supplied by the raw (sea) water pump. The solution were to install restrictors in the cooling system to reduce the amount of water being pumped over board via the exhaust manifold. This type of fix worked vey good in a certain RPM range i:e, from idle up to say 3/4 of the RPM range. Beyond that and the engine will over heat again because the water is moving too slow (remaining in the block too long) to take the heat away.

Many large stationary engines of the past as well a marine engine that were installed in a manned engine room had valves to control the flow of the coolant. It was necessary to regulate the flow in order to maintain optimum engine temperature.

Fast forward to our NAXJA forum. There are /were a few XJ enthusiast on here that installed a free flowing thermostat, a free flowing thermostat housing and a high volume water pump. There result? The 4.0L was plagued with over heating. These persons installed restrictors of one sort or another to reduce the flow of the coolant which as they claimed accomplished the desired results. This is exactly what I used to do back in the islands with some margin of success.

So the question is, Why does my XJ over heat? Maintaining a good working cooling system have been discussed many times on this forum. I will not get into that topic. A little searching will yield more info that one can digest in a lifetime.

In closing, I must say this,.... the design of the XJ 4.0L cooling system however marginal it is, in my opinion have adequate coolant flow. High volume water pump, thermostat and thermostat housing are not needed. The OEM thermostat, thermostat housing and water pump in good condition are quite capable of flowing more coolant than is necessary. A good quality thermostat is the automatic flow regulator. Nothing more is needed.
 
From my education and experience thus far I have always eventually been able to reconcile instances where real-world experience SEEMED contradictory to the science. This specifically happened with traction about a year ago, where the general consensus was "wider tires increase friction with the road" which in fact they do not. The formula for friction does not include surface area anywhere in it. Long story short, I studied it and discovered that it actually had to do with shear...and people freely switching between the words traction and friction...which we cannot do. Do wider tires increase TRACTION? Yes. Do they increase friction? NO. I am 100% confident that this is a similar situation and if no one beats me too it, I will eventually understand and share what is happening and why we perceive the cooling results the way we do. The difficulty with analyzing real-world examples is that they are always fraught with many unknown variables. I'll revisit this when I get to my Heat Transfer, Fluids, and Thermal and Fluid Systems classes. :)
 
yossarian19 said:
So, Qban - any news?
Click to expand...

The news is that I just got back from a week in Maui =)
The weather and surf was excellent. There were some large sea turtles, eagle rays, and a ton of tropical fish and coral to view while snorkeling. I got car sick on the road to Hana but at the end was an amazing hike through a bamboo forest and a view of a 400ft waterfall. Zip lining was fun and my friends wedding was a great and touching end to the trip.

Now its time for me to get the jeep working again. I just finished reading the last couple of posts. The discussion on water flow was interesting as I'm a computer engineer who hasn't had much mechanical experience. I have a ton of catchup to do at work, so hopefully this weekend I'll have time to actually fix this.

Thanks
 
I also have a 97 with a heating problem. I have replaced the radiator with a flex-a-lite aluminum radiator with three fans a new Alabama head new hoses new water pump new thermostat and I drilled a weep hole in it for air .040. and it still ran warm. So today I replaced the sensor and it lowered the temp to a good level by the gage. So I drove down to the valley on the way home up the 14 it got warm. The next step is pressure test to see if it holds. I am going to find out what the problem is and I will post it to try and help others with this problem.
 
So here's my latest after the weekend.

I had a friend who's more of a backyard mechanic than me come over. We pulled the valve cover and inspected everything then put it back on. From under the jeep looking up on the drivers side of the block we found what looked like some seepage from the head.

I put everything back together with the new radiator, changed out all the factory spring clamps for worm gear clamps. I cleaned the top rad hose, the bottom one is new, replaced the heater hoses (which the heater is currently bypassed). I put 2 holes in the thermostat 12 and 6 oclock. Put everything together and pressure tested the coolant system, It held at 16psi just fine. I bleed the system and filled back with 50/50 and some some redline water wetter.

I took it for a drive and thought everything was pretty good, it was a lot better than with my old oem radiator and a lot better than without the tstat and without the leak I found previously.

I thought everything was going great till after about 10min at 65mph, then overheat again.

Because of the "leak"/seepage we found around the back of the head, I'm taking it to a mechanic at my work and I'm going to have him take a look at it and do whatever test he thinks.

Thanks everyone! I'll keep up to date with what happens cause I'm sure everyone is dying to find out =) haha...
 
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