Engine Cooling - Master Thread

[ghetdjc320]

I thought I’d start a thread on the frequently recurring topic of engine cooling. I’d love to see some club input on the various problems/solutions to this issue. Something we can reference going forward. Obviously, there are many factors that contribute to overheating but I wanted to touch on a few common ones along with some of the common fixes. 
 

All too often we see some new cooling system “upgrade” that touts some miraculous cure for overheating. But did it actually improve something or just fix something that was broken or that was already end of life? The ones that we see a lot of are (in no particular order): 

1. High flow water pumps

2. Multi-Core radiator upgrades 

3. Triple e-fans or a variation thereof

4. Water wetters and coolant additives

5. High flow thermostat housings

6. Hood vents 

7. Heat shielding products

8. Low temp thermostats

Anything else I’m missing on this list??

 

The underlying overheating issue we see (in no particular order)

1. Clogged or dirty radiator/coolant passages 

2. Bad water pump

3. Coolant system leaks

4. Cracked block/head/blown head gasket

5. Lean running condition 

6. Incorrect coolant fill

7. Bad thermostat

8. Failed Renix temp/fan switch

Anything else I’m missing on this list?

 

 

[Eagle_SX4]

If the Renix radiator mounted temperature switch fails the e-fan won't turn on leading to overheating issues.

 

I installed a 200 degree temp switch into a H.O. thermostat housing that I ported and the fan comes on more but I don't have to worry about overheating issues now. If I recall the Renix temp switch is set at about 215 degrees, but I think that is too high. Your fans should be on before you start to overheat. I would like to get a newer e-fan with the 9 or 10 blade design but I haven't come across one in the junkyard yet.

 

The thermostat housing is restricted and can be ported to allow better flow through it. I only noticed when I swapped my 4.2 thermostat housing for a H.O. housing. The housing was closed off to prevent the thermostat from being install backwards but it severely shrank the port size. The Renix and H.O. housings are the same other than the port for the temp sensor.

[Comanche SS]

99% of the 20+ XJ/MJ's ive owned have had much better cooling performance for less than $40...

If you wash/backwash/wash the radiator, engine, and heater core (all separately/individually so you don't move contaminents) then install a new fan clutch I can almost guarantee you'll have a cool running jeep.

The amount of crud that comes out with the wash and backwashing of the system is really impressive. Then the fan clutch thats likely never been replaced makes a huge radiator efficiency difference. 

just my 2c, I do this service on every Jeep thats comes thru my possession and it almost always makes it run cooler/properly.

Edit to add: The mech fan with a proper working fan clutch or grand cherokee clutch will almost always out perform an electric fan, or two. Always run the mech fan unless you can't for some reason.

[Limeyjeeper]

Lean running is a bigger issue than people think. It can increase the operating temp of an engine dramatically. A lot of Stroker cooling issues are lean running related. I am not saying that the other issues aren't relevant but don't underestimate tuning particularity with a stroker or an LS swap.

[derf]

I will add my x2 to the proper cleaning of the cooling system, as well as having a good quality fan clutch and mechanical fan.

 

I will add that you should also wash the outside of the radiator between the fins.  And ensure that most or all of the fins are straight.  If you have debris or damage blocking air moving through the radiator, nothing else you do will keep you from overheating.

 

That's the low cost step you should take first every time.  If you're still overheating after that, then you have to do more diagnosing.

[ghetdjc320]

25 minutes ago, Limeyjeeper said:

Lean running is a bigger issue than people think. It can increase the operating temp of an engine dramatically. A lot of Stroker cooling issues are lean running related. I am not saying that the other issues aren't relevant but don't underestimate tuning particularity with a stroker or an LS swap.

Agreed. A lot of LS swaps I see don’t properly address the fuel pump. They just think that if it can hit X psi at idle than it’s good to go. They don’t seem to understand fuel demands under load. Interestingly, on my YJ stroker I built back in 2016, I installed a Holley terminator tbi setup.  It was definitely running rich. The interesting side effect is that I could not get my engine up to operating temp quickly. I had very little heat in the winter and always ran cool. Never went above thermostat temp and was very slow to even get to that point. On the other hand, a performance built 4.0 I had in my first MJ had lean running condition and every so called “upgrade” cooling component in the book did nothing to fix the issue. I ended up needing to wire in a fixed resistor into my CTS circuit to help the engine think it needed a richer mixture. After that, problem solved! Oddly enough, the hotter an engine gets, the leaner the ecu seems to adjust the fuel trim 

[ghetdjc320]

7 minutes ago, derf said:

I will add my x2 to the proper cleaning of the cooling system, as well as having a good quality fan clutch and mechanical fan.

 

I will add that you should also wash the outside of the radiator between the fins.  And ensure that most or all of the fins are straight.  If you have debris or damage blocking air moving through the radiator, nothing else you do will keep you from overheating.

 

That's the low cost step you should take first every time.  If you're still overheating after that, then you have to do more diagnosing.

 

41 minutes ago, Comanche SS said:

99% of the 20+ XJ/MJ's ive owned have had much better cooling performance for less than $40...

If you wash/backwash/wash the radiator, engine, and heater core (all separately/individually so you don't move contaminents) then install a new fan clutch I can almost guarantee you'll have a cool running jeep.

The amount of crud that comes out with the wash and backwashing of the system is really impressive. Then the fan clutch thats likely never been replaced makes a huge radiator efficiency difference. 

just my 2c, I do this service on every Jeep thats comes thru my possession and it almost always makes it run cooler/properly.

Edit to add: The mech fan with a proper working fan clutch or grand cherokee clutch will almost always out perform an electric fan, or two. Always run the mech fan unless you can't for some reason.

Very good info. I’ll add this to the list above under “Solutions that work” or something to that effect. I don’t run a mech fan at the moment but can definitely attest to how well they work. 
 

When it comes to cleaning/flushing, do either of you use any chemicals?

[ghetdjc320]

1 hour ago, Eagle_SX4 said:

If the Renix radiator mounted temperature switch fails the e-fan won't turn on leading to overheating issues.

 

I installed a 200 degree temp switch into a H.O. thermostat housing that I ported and the fan comes on more but I don't have to worry about overheating issues now. If I recall the Renix temp switch is set at about 215 degrees, but I think that is too high. Your fans should be on before you start to overheat. I would like to get a newer e-fan with the 9 or 10 blade design but I haven't come across one in the junkyard yet.

 

The thermostat housing is restricted and can be ported to allow better flow through it. I only noticed when I swapped my 4.2 thermostat housing for a H.O. housing. The housing was closed off to prevent the thermostat from being install backwards but it severely shrank the port size. The Renix and H.O. housings are the same other than the port for the temp sensor.

Added the renix temp sensor issue to the list. I’ve been curious about the ported HO mod. I’ve heard two lines of thought on this, one is that the restriction assists in cooling by slowing the coolant flow a bit out of the block to aid in heat transfer. The other is that it’s for thermostat orientation as you mentioned. I know when I swapped to a high flow pump and the high flow housing with a still stock size radiator, I felt the water was moving to fast to effectively transfer the heat. 

[89 MJ]

I'll agree with everyone that flushing the cooling system is absolutely crucial.

 

I'll throw my experience out there, what I think some of my culprits were, and how I fixed it.

For full transparency, here is my setup: 96 4.0 block, head, and exhaust manifold, stock Renix engine management, a high altitude CPS, a bored throttle body, stock fans, AX-15, 31s, and 4.10 gears. 

 

Running on the interstate (figure 72-80 mph range depending on traffic flow), my truck would overheat over time.

The first time took roughly 40 minutes. This ended up being a partially clogged radiator. 

The second time happened after about an hour and a half. I believe I have solved this with a high flow water pump, the truck stays near 195-210 now.

 

I think that there are a few things to blame here.

1. Obviously the radiator was bad (the block was spotless when it was installed)

2. High altitude CPS advances timing something like 5*. Too much timing does make an engine run warm and my truck has lived around 900 feet of elevation during my ownership.

3. The heater core was partially plugged and has since been replaced.

4. Sustained RPM. My truck turns ~2750 RPM at interstate speeds. That is a lot of RPM for a long time when I don't think that the cooling system was designed for it. Ultimately, my truck wanted a high flow water pump to deal with this.

[Limeyjeeper]

35 minutes ago, ghetdjc320 said:

Agreed. A lot of LS swaps I see don’t properly address the fuel pump. They just think that if it can hit X psi at idle than it’s good to go. They don’t seem to understand fuel demands under load. Interestingly, on my YJ stroker I built back in 2016, I installed a Holley terminator tbi setup.  It was definitely running rich. The interesting side effect is that I could not get my engine up to operating temp quickly. I had very little heat in the winter and always ran cool. Never went above thermostat temp and was very slow to even get to that point. On the other hand, a performance built 4.0 I had in my first MJ had lean running condition and every so called “upgrade” cooling component in the book did nothing to fix the issue. I ended up needing to wire in a fixed resistor into my CTS circuit to help the engine think it needed a richer mixture. After that, problem solved! Oddly enough, the hotter an engine gets, the leaner the ecu seems to adjust the fuel trim 

People don't realize how much fuel cools an engine.

[ratrapp]

 i tried the hesco high flow pump and t stat housing many years ago my old 88 and seen absolute 0 difference except a water pump that lasted no time.the water wetter i tried on different vehicles and it was a waste as well.

[Eagle_SX4]

The ultimate reason I switched to the open system was due to failing pressure tank caps. My truck nearly over heated twice because of a failed cap. It seems like the biggest reason to switch to the open system is to eliminate that tank.

[derf]

1 hour ago, ghetdjc320 said:

 

Very good info. I’ll add this to the list above under “Solutions that work” or something to that effect. I don’t run a mech fan at the moment but can definitely attest to how well they work. 
 

When it comes to cleaning/flushing, do either of you use any chemicals?

For the exterior wash, I may use soapy water.  Or just water.

 

It's important to have some pressure to blow the gunk out.  But too much pressure can fold fins over and that causes blocked airflow.  You need a Goldilocks "just right" flow when washing.

 

As far as inside the block, I haven't done a ton of research on the various options and products. Most of my block cleaning has taken place while at the machine shop for a rebuild.