New cooling system overheating on the highway

The original radiator was was due for replacement. Many collapsed fins, corrosion, etc so I opted to replace. Considering I was going to be relocating to a much hotter area I went with the Flexalite with the three e-fans.

Motor is stock with the exception of the Hesco hi flow water pump.

Ambient temp averages about 103' during the day.

At idle the XJ does great. It will sit between 198' & 202'
At speeds up to about 35MPH it runs at 209'-211'
Above speeds of 35MPH the temp rockets upwards of 225'. I imagine it would go higher but when it reaches the mid 220s I take action to cool it down such as reducing speed down to <15MPH or stopping completely and letting it just idle. This is all without running A/C.

Coolant mix has been played with 70/30 & 50/50. I didnt see the bottom hose collapsing from the Hesco pump but I swapped to a reinforced hose anyways. Plugs are new with proper gap. No know vacuum leaks. Air burped with drivers side elevated.

There is a winch however, it sits pretty low leaving the upper 2/3 of the grill exposed. I also have hinge blocks installed so the rear of the hood is elevated about 1.5" allowing for air pass through.

Rad install was strictly by the book.

It really seems backwards to all overheating problems I have ever experienced. I don't know if it is load related or airflow related.

Any ideas?

Thanks in advance for any input!

What kind of radiator did you buy?

Cracked head?

Nope,head is good. Its a new mfg. Casting was nice and clean... Not much slag to be cleaned up.

Flexalite with their 3 e-fan set up specifically for the XJ.

How many rows is the radiator? What is the gear/trans/tire size?

Picture of grill- I don't think it's too obstructed

I think its a three row

Gearing is stock

Tires are 32"

With stock gearing on 32's is it possible with a three row radiator that you aren't pushing the coolant thru fast enough? If you hold 2nd gear at 35mph will it stay cool? I could be way off, just a thought.

From what you are describing it SOUNDS like there is no thermostat in there and coolant does not have time to actually cool in the rad...flowing too fast.I am sure you do have one installed.The only thing I could sugest is to have a scanner installed to monitor actual temp and compare to gauge.OR the e-fan controller needs to be re-set or it's sensor is bad.I do not know how the e-fans come on/controlled.

Raising the rear of the hood is the wrong thing to do - that is a high pressure area when you are on the highway. You are basically pushing air back into the engine compartment and not allowing air to flow through the radiator. Pull the spacers out and go for a test drive.

I will try holding a higher RPM at about 35MPH and see what happens.

I do have a t-stat in place. I had a 195' and just to see what would happen I swapped it with a 180'. I do see a difference. It simply starts cooling sooner. I tested a couple 195s and both didnt start opening until about 203'. The 180' opens at about 183'. I left it in there as it seems to keep it closer to 210 during the 25-35MPH range without spiking higher before returning to the 207-210 range.

Just to see what would happen under load I found a road with a slight incline and held a smooth 35 MPH. The temp rose quickly.

So the load on the engine has a direct influence on the temp. A slight incline, A/C pump, or solid acceleration raises the temp almost immediately. Pulling over and letting it idle for a few minutes drops it right back down to 198'-202' within 2-3 minutes. The dropping of the temp within that short of time tells me the cooling system works great.

The temp rising while under load is what leads me back to a collapsing lower hose or something along that line. I was told by the guy at NAPA that the hose that they sold me would not collapse. However, it doesn't seem firm enough for me to full heartedly believe it. I have another hose with an interior wire structure but my concern is that it is not formed with all the correct bends, etc and I would hate to place to much stress on the aluminum neck coming out of the radiator.

Thank you all for your thoughts. I'm trying each of them.

DieselSJ said:

Raising the rear of the hood is the wrong thing to do - that is a high pressure area when you are on the highway. You are basically pushing air back into the engine compartment and not allowing air to flow through the radiator. Pull the spacers out and go for a test drive.

Click to expand...

I was told the exact opposite. I was told it would allow air to flow through the radiator easier by allowing it to pass through the radiator and having a place to exit the engine compartment other than down, much like louvers.


I will try that next. It only takes a few minutes to remove those blocks.

I have the lower radiator hose with coil in it and it fits perfectly. $20 from the dealer. Your temps should rise when the engine is under load. Mine runs just above the thermostat temp of 195, but if I'm climbing a steep grade on the highway in summer heat while carrying a lot of gear the temp will hit 210-215. Raising the rear of the hood lets hot air out at idle or low speeds but doesn't do anything at speed.

32's and stock gears generates massive amounts of heat in an AW-4. You are using 3rd and not OverDrive (OD) on the highways, right ? You are saving for new gears, right ? 16 lbs radiator cap ? The base of the windshield is low pressure, IDK if the raised hood helps or hurts on the highway. Hood vents end up in a low pressure zone, pulling hot air out.

Do you have any power issues? Almost sounds like cat is clogged up.

When did you last mess with the cooling system? Could be the thermostat is backwards, it will do what you describe

Also, let it warm up and then try holding 2k rpm in your driveway for a minute and see if it heats up the same way.

Drop an OEM tow package rad in there. you can get them for 160 dollars. A lot of the aftermarket rads especially 3 row rads don't work as well as the OEM ones.

HWK9USA said:

I was told the exact opposite. I was told it would allow air to flow through the radiator easier by allowing it to pass through the radiator and having a place to exit the engine compartment other than down, much like louvers.


I will try that next. It only takes a few minutes to remove those blocks.

Click to expand...

Again, it is a high pressure area when you are at speed. That would work on the trail, but not on the freeway. That is the same reason why you want louvers as close to the front of the hood as possible, or off to the edges. Have you ever watched the water on your hood when you go down the freeway in a rainstorm?

Tim_MN said:

The base of the windshield is low pressure

Click to expand...

This is incorrect.

Read: http://www.gmecca.com/byorc/dtipsaerodynamics.html

It is not full time 4x. I do have a 16 lb cap

I pulled the blocks from the hood hinges. It didnt seem to make a difference either way with cooling so I will probably keep them off.

This is really becoming frustrating. I drove about ten miles this morning on a flat road doing about 50 MPH. Results were completely opposite of previous experiences.

After accelerating, stopping , etc I reached the last turn before the flat 10 mile stretch. Approaching the light I was at 217'. When the light turned green I was down to 207'. Expecting to see a steady climb in temp once I started heading down the road I was surprised to see a steady DROP in temp while doing a solid and stable 50 MPH. 205', 202'.. Down to 197'. The remainder of the road kept me bouncing between 197' and about 202' This was the first time ever since the install. I reached the parking lot of my final destination and prior to parking I had reached 222'. This is completely opposite of previous experiences. Normally it would be dropping in temp any time I am at an idle with relatively no load.

Returning home down the same 10 mile road things were back to normal where at 50 MPH temp was gradually rising. It almost made me wonder if there wasn't possibly something in the reservoir blocking coolant flow through one or more of the veins and during higher RPMs it gets pulled into the higher flow area and blocks flow.

I'm going to try to idle at 2000 rpm as mentioned by the poster as something to try.

I spoke with Flexalite whom suggested I double check that the fans are pulling through the rad rather than blowing which would create a stagnate pocket of air while at highway speed. Fans are pulling air from in front into the engine compartment.

Regarding the hose from the dealer- That was my first choice. However when I called for availability the person said it would have to be ordered. I asked about a spring being with it to which he stated that there is a note on the page however when he clicks on it nothing is there. He had no way to verify if a spring came with it. He also stated that they only use the spring on OEM at time of MFG stating that during assembly when filling the system with coolant it is done under vacuum so that they dont have to burp it and because of this is the only reason the spring is needed. So unless I am filling coolant under vacuum he sated I dont need it. Ive read too much to the contrary to fully believe that.

HWK9USA said:

It is not full time 4x. I do have a 16 lb cap

I pulled the blocks from the hood hinges. It didnt seem to make a difference either way with cooling so I will probably keep them off.

Click to expand...

This is really becoming frustrating. I drove about ten miles this morning on a flat road doing about 50 MPH. Results were completely opposite of previous experiences.

Click to expand...

Those statements are contradictory.

My mistake. I didnt add the part about the blocks in chronological order. It was added as I was trying to remember the help and advice given from each of you. and make sure I replied regarding each.

The blocks were taken out after I got home. I didnt notice any difference with them out while idling in the driveway or during the short trip around the neighborhood.