Using Cooling System Restrictors to Stabilize Temperatures

[HOrnbrod]

Since I got my A/C up and running awhile back, I haven't liked the engine temps on super hot (~100*F) days. The A/C works fine, but the engine temps start to creep up while it's on, especially in traffic. Never all the way to the red zone, but close. I read THIS article on Marcus's (Gojeep) web site about the use of restrictors in the system to stabilize engine temperatures. Since his XJ cooling system is similar to mine (Hesco high flow water pump with twin electric fans) I thought I'd give it a try. If you read the whole article, you will see that Marcus found the best size restrictor for his system turned out to be the 1/2" size. I cut out three restrictors out of a nylon board exactly like his in 7/8", 3/4", and 1/2" sizes; the 1/2" and 3/4" sizes are shown below. After trying all three restrictors for a few days each, the 3/4" size gave me the best results. I've been driving around for two weeks now with the 3/4" restrictor in the radiator upper hose, and my temp gauge stays rock solid straight up. On the hottest days stuck in traffic with the A/C running, the indicator goes slightly to the right of center about two needle widths max., then quickly moves back down when I get moving again.

 

This mod really did work for me, and my engine temperatures have never been so stable. Overall it runs cooler too. It's worth a try if your engine runs hotter at times than you'd like it to. The only thing I'd add to his writeup is to use an extra hose clamp around the restrictor washer that's inside the upper hose to keep it from moving as in the pic below.

[Eagle]

Same idea as the old-time stock car racers trimming the impellers on their water pumps.

 

Does this suggest that the high-flow water pump isn't a great investment?

[HOrnbrod]

It doesn't "suggest" anything except that cooling system efficiency can be improved. Read Gojeep's article. Many manufacturers use restrictors of varying designs in their cooling systems.

[schardein]

I"ve read that article and wondered if it would help.  

 

I'm am going to repair the AC in my XJ, MJ, and Chevy.  Recently did a 1500 mile trip in the XJ with no AC and on hot afternoons and going up slight grades, the temp would rise.  Kicking on the heater would bring it back down.  Not fun running the heater with no AC and its 95 degrees out.

 

What size did you cut the outside diameter?

[HOrnbrod]

Same as Marcus used.

 

Used a 1 3/4" hole saw that left a 1 5/8" plug to use.

[sinkrun]

Very good info and I have a bar of Aluminum and a lathe would make a nice project

[HOrnbrod]

Very good info and I have a bar of Aluminum and a lathe would make a nice project

 

:thumbsup:   Please post up your results when tested. 

[Eagle]

It doesn't "suggest" anything except that cooling system efficiency can be improved. Read Gojeep's article. Many manufacturers use restrictors of varying designs in their cooling systems.

 

But the improvement in efficiency is created by slowing the flow of coolant through the radiator so there's more time for the heat to be transferred from the coolant through the tubes and fins and into the air. That's the reason the racers trimmed the impellers -- to make the system move LESS coolant at high RPMs. That's essentially what the restrictor is doing, and it seems to counteract the purpose of a high flow water pump.

[sinkrun]

 

Very good info and I have a bar of Aluminum and a lathe would make a nice project

 

:thumbsup:   Please post up your results when tested. 

 

Looks like someone already makes them I do like the tapered ID for flow. They also sell the washer type in a kit with 3 different.

 

http://www.ebay.com/itm/Allstar-Performance-1-3-4-in-Aluminum-Radiator-Hose-Restrictor-P-N-30242-/142084005752?hash=item2114dddf78:g:n8YAAOSwgZ1Xrod5&vxp=mtr

[schardein]

 

 

Very good info and I have a bar of Aluminum and a lathe would make a nice project

 

:thumbsup:   Please post up your results when tested. 

 

Looks like someone already makes them I do like the tapered ID for flow. They also sell the washer type in a kit with 3 different.

 

http://www.ebay.com/itm/Allstar-Performance-1-3-4-in-Aluminum-Radiator-Hose-Restrictor-P-N-30242-/142084005752?hash=item2114dddf78:g:n8YAAOSwgZ1Xrod5&vxp=mtr

 

Ebay ad indicates for use in the lower hose... wonder if it makes a difference?  

[HOrnbrod]

That's a generic restrictor, not specific to the Jeep 4.0 upper or lower hoses, which have different ID's. The item description doesn't even give the ID of the small-end of the taper. You'll need to find out all that info first.

[64 Cheyenne]

 

It doesn't "suggest" anything except that cooling system efficiency can be improved. Read Gojeep's article. Many manufacturers use restrictors of varying designs in their cooling systems.

 

But the improvement in efficiency is created by slowing the flow of coolant through the radiator so there's more time for the heat to be transferred from the coolant through the tubes and fins and into the air. That's the reason the racers trimmed the impellers -- to make the system move LESS coolant at high RPMs. That's essentially what the restrictor is doing, and it seems to counteract the purpose of a high flow water pump.

 

 

I've thought about this for a while now and is the reason I haven't purchased a "high flow" WP.

Gotta give the radiator time... to... transfer.... heat...insteadofgetitthroughathighflowandvolumerightnow!

[Marine1Texas]

Since I have had my 87 MJ 4.0 never had a cooling issue at all. Even when it is 110 here in Texas it has never gone over 205. When I turn the a/c on it over cools and stays right around 195 even sitting and idling for long periods of time. Even with a non vacuum line hooked to EGR it does not heat up. I think the biggest issue with temps not maintained cooling liquid. I like a 70/30 water/antifreeze in my MJ. I always thought the thermostat was a good restrictor by its self. I could see a thermostat that had a even less of a opening would slow the flow as well. that my 2 cents lol

[Ωhm]

Does this stabilize temperature or does it just stabilize the gauge in the dash? Seems like a simple fix and I hope it works well. Anyone know if the ECT is affected by this? Like I said, hope this works.

[1989 comanche mj]

I use less coolant also, 10 percent antifreeze 90 water.  It never freezes here in Florida.  When I go north I adjust coolant to the lowest temp for the area. 

[TheDude]

I'd be interested to check various spots on the engine with a Infrared Thermometer to see how it affects the temp all around compared to stock.

 

 

1989 Jeep Comanche 4.0L 5 Speed 4x4 Long Bed

1991 Jeep Comanche 2.5L 5 speed Red Short Bed

[A-man930]

This is quite interesting.  I'm with Eagle; sounds like the high-flow water pump is of little benefit if you just end up choking it with a restricter...

[DirtyComanche]

 

It doesn't "suggest" anything except that cooling system efficiency can be improved. Read Gojeep's article. Many manufacturers use restrictors of varying designs in their cooling systems.

 

But the improvement in efficiency is created by slowing the flow of coolant through the radiator so there's more time for the heat to be transferred from the coolant through the tubes and fins and into the air. That's the reason the racers trimmed the impellers -- to make the system move LESS coolant at high RPMs. That's essentially what the restrictor is doing, and it seems to counteract the purpose of a high flow water pump.

 

 

From a perspective of thermodynamics, which is law, it is always more efficient to move the coolant fast.  There is no need for a 'soak' or 'dwell' time to allow for energy transfer, as it is a closed system and the coolant is being recycled into the engine.  It's all input BTUs vs output.

 

What is happening here is the pump flows too much for the thermostat to operate satisfactorily.  Instead of it allowing a trickle flow into the radiator, and thus a trickle flow of colder coolant back into the engine, rather as the thermostat opens there is a large 'slug' of cold coolant that is transferred into the engine.  The resultant is shock cooling, and rapid shutting of the thermostat.  The system (the engine) then has to bring this coolant back up to temp before the thermostat will reopen.  Since the gauge is reading the back of the cylinder head, the area which is prone to poor flow and higher temperatures, it sees a different story than the thermostat does, since the thermostat is at the front where flow is higher, the end result is the coolant in the area of the sensor will become much hotter in the lack of flow situation caused by the thermostat shutting from the cold coolant slug.

 

I am with you, a high flow waterpump is NOT always a good idea.  This mod is effectively taking the high flow pump and turning it back into a normal one so the system is balanced correctly.

 

If there was a better thermostat and housing design (look at the GM LS series of engines for example) there would not be a need for this mod with a high flow pump, which would also allow for the high flow pump to actually have 'high flow' in the event that the cooling system neared saturation and the thermostat was operating at full open continuously.

 

If none of this made any sense it's because I got into the gin, and will explain better later...

[DirtyComanche]

To expand on the soak time comment, basically heat/energy transfer is faster as the delta-T (temperature differential) is higher.  To put it simply, if you microwave a bowl of water until it boils, and another until it hits 80*C, the boiling bowl will drop from 100* to 80* faster than the second bowl will drop from 80* to 60* (and that's while ignoring the effects of phase change from the boiling bowl).  If coolant flow is low, there is enough time for it to cool considerably as it crosses the radiator, meaning that by the time the coolant gets half way across the radiator it will have no where near as great of delta-T, and thus energy is not being transferred out of it nearly as fast.  This is inefficient, as half of your radiator is not doing nearly as much 'work' as the other half.  If you increase flow the coolant in the radiator will always be hotter, thus keeping the delta-T high, and will transfer more energy out in the same time period.  A high flow pump excels for this, and will keep a system that is nearing saturation from boiling over (or reaching a dangerous temperature) simply by moving the hot coolant fast enough that enough efficiency is picked up across the whole radiator by the higher delta-T.

 

Of course you actually need to be generating enough heat energy, and be shackled with a high enough ambient temperature, for it to matter first.  And then we're back at the whole issue of regulating it given that both those things are variables.  Racers have a lot of workarounds for this.  Restrictors are something they use, but they may change them according to ambient conditions, and often they use them without a thermostat, or a thermostat that has a hole drilled in it or a bypass installed to allow for a minimum flow.  Likewise, clipping pump blades changes flow, or filling certain water jackets to redirect flow, or changing the shape of the inlet or outlet housing.  There's whole books written on it, some by people who knew what worked based on the theory, others by people who knew what worked by trying it.

[DirtyComanche]

And I could be wrong on any or all of this.  See previous comment about gin.

[HOrnbrod]

See post #1 of this thread for reference - ignore the rest to save time. Lately in our 90*+ weather, my engine temps have increased closer and closer to the red area on my gauge than normal, especially when running at slower speeds. Did a good flush and coolant change, no help. Went back through Gojeeps writeup, see the first post, and since we have similar cooling systems using the Hesco hi-flow water pump, I decided to try the 1/2" restrictor left, below) like he is using vs. the 3/4" restrictor I had installed previously. Fabbed one up, installed, and immediate relief. I couldn't get the needle off the straight up position in the last week no matter what I did or what the weather - rock solid under all conditions. Should have used the 1'2" first, but it looked so small I didn't want to try it. Gojeep truly knows his stuff. If/when my Hesco pump craps out, I'll swap in a new Mopar stock pump and then maybe lose the restrictor. But until that happens. I'll stick with the temp stability I have. Too many $$ invested in the stroker and the peripherals to screw around..

 

[dvitha]

The setup I like to use a multi core radiator like on jeep a 3 or 4 core with normal and high flow. The more area that is allowed to exchange heat allows for better temperature exchange. Now with a larger area of heat exchange it allows the system to handle higher flowing coolant. However higher flowing does take away from heat exchange from block to coolant, but when you double, triple or more the core the area of exchange of heat you have better cooling. Now at slow flow, it allows for greater time to heat soak the coolant in the engine block.

 

In the shop my shop our we have two kind of racers. 1st the fast all out ones dragging. They like to use normal flow with very small cooling systems, because weight is key. Now they don't run them for long and don't cool well at idle. 2nd we have the all the time go long racers. There are 2 kinds slow and fast movers. The fast long track laps they like to use normal flow, with multi core 4 +. They don't have fans in their applications, so they require the movement fast air flow. Then we have the slow track mud racing. Since the dirt and the slow speed they have high flow and 2 to 3 core system with 2 fans some times 1 large one.

 

Now that's for the racers we support here near our race track. Our off-road customers, which normally are moving better than a craw but not street speeds they like the high flow multi core 3 to 4 systems with 2 to 3 electric fans.

 

We also do big trucks here that haul like diesels and large v8's. It is standard for as multi core as possible and normal flow pumps. Most the systems hold so much coolant that by the time it gets around the system a large amount of cooling has happened.

 

Since all our jeeps at the shop are highway and local speeds of 45 plus, we go with normal flow and multi core 3 or 4 core with electric fan setup. Since high speed allows for air flow better than the fans can provide, the fans shut down and less stress on the electric system.

 

So basically it all comes down to what you need. If your spending most of your time crawling, and less air flow, multiple electric fans, with a  multiple core radiator and high flow allows for best exchange. Now in a 50/50 or higher I think staying with normal flow and multiple core is the trick for most of our jeeps. Those who keep there mechanical fan with the 1 electric fan will cool at good optimal temps when slow. However a 2 or 3 fan electric setup would allow for more verse able cooling since the system can come on and shut down when not needed.

 

Here ins Texas heat is one of the biggest factors, so at least 30% of the customers we get is about radiators and cooling.  In the last 2 years many customers have gone to closed waterless cooling. It puts less stress on the system, hoses last longer, pumps last longer and I have not had a unhappy customer yet who used it.

[zomeizter]

HOrn, you speak of a high flow coolant pump and am wondering if all you need is a radiator (larger or with more cores) to complement/take advantage of this high flow to "stabilize" the cooling system? Maybe some better cooling fans that move more air while idling and at a stop with the A/C operating? If you do go with a conventional water pump and that cures the issue, then the engineers commenting previously are right, there is a happy median for coolant flow, given all other components and fluid levels are proper. This interests me lots since I've been "upgrading" the cooling fans on my fleet and have noticed that high air flow during engine idling and using A/C does nothing when the coolant flow is under par due to restrictions in the rad core tubes, holler...

[HOrnbrod]

THIS

explains coolant flow vs. heat transfer it much better than I can. I think the Hesco water pump pushes coolant through the system faster than the heat can be transferred off. The restrictor slows down the flow and stabilizes the heat transfer. The high-flow pump comes with the stroker package, so I'll run it until it breaks, then probably slide a new Mopar pump in. At that point I'll probably be able to get rid of the restrictor. I'm just happy to be able to control and stabilize the engine temps so easily.

[zomeizter]

Thanks for the link, now I understand why the restriction works ...carry on.