Engine temp and towing

Let's talk cooling. How hot is too hot when towing?

Current Jeep setup: New aluminum radiator, new water pump, new 195* t-stat, heater core bypassed, new fan clutch, 30" tires, 3.73 gears. Ambient temps between 70*F and 80*F. To run 70mph on the interstate I'm turning 3100 rpm (5200rpm redline) with the OD off.

With the AC on max and maintaining 70-75 mph I was seeing the temp hit 224*F on long shallow hills, might have continued to creep up but I chickened out. Turning the AC off dropped it about 10*.  I backed down to 65mph and it dropped to a steady 200, even with the AC turned on. 

Off the interstate and running 55 it runs 196-199 with the AC blasting, which seems pretty good with a 195 t-stat.

It currently has the (somewhat leaky) factory trans cooler in front of the AC condenser, which is partially coated with dirt and trans fluid from the leaky cooler. I've pressure washed it, but there's still some fins blocked down low. Whenever I pull the front end apart to replace grill structure and headlights, I'll have access to scrub up the condenser. I'll also be installing a larger trans cooler that I have sitting in the shop.

What do you think? Is this running in what you'd consider a normal range? I'm a little concerned about towing for 3 hours at 65 this summer in 95*+ ambient temps with the AC honking.

I'm reposting this as a new thread since no one reads my ZJ thread anymore.

My XJ runs 200-220 towing at 70 with the A/C on. The ECU doesn't turn the electric fan on until around 215 degrees. 

Larger trans cooler is going to block more direct airflow to the radiator. Wouldn't be surprised to see engine temps climb higher as a result.    Is there room to mount two smaller units outside of the main grille area like in front of the tires,  with protective ductwork to avoid debris from off roading?Improving engine radiator flow, while still improving trans cooling.  Does  your jeep have a stock oil to water (internal radiator) trans cooler? If so, are you planning to bypass that with the install of larger aux trans coolers?  That would reduce the load on the engine radiator to keep the engine cool, but I suspect you'd have a harder time keeping the trans cool. 

  Like you mentioned, the easy answer is to slow down a bit, 65-70 is about the max speed you should be cruising with a trailer anyway. 

On an engine with iron block / heads, I'd say anything up to 220 - 225 is fine for continuous use.  Short runs up to 230 shouldn't hurt anything, but I wouldn't really want to see it hotter.  

It sounds like you've got the same issue as my Jeep.  Once you bring the speed above 55 or so, engine bay airflow starts to get worse, not better.  Cruising at 50 with 5k lbs of trailer behind my Jeep and the A/C on or just driving around town, it'll sit around 200 - 210.  Get on the highway and cruise at 65, it'll run 215 on flat ground.  Point it uphill and the temp will just slowly climb all the way up the hill and then drop down to 195 coasting down the other side.  It's just an issue of not enough radiator and not enough airflow.  

Does the XJ run electric AND mechanical fan, or just the electric? 

ultraclyde said:

Does the XJ run electric AND mechanical fan, or just the electric? 

 

XJ has both (side by side, as the radiator is very short and wide).  I'm e-fan only in my ZJ (5.9).  I'm planning to try one of the thicker radiators for it from eBay this summer, so we'll see how that helps.  Others have had luck by cutting big vents into the ZJ hood to get heat out.  FWIW, I have a trans cooler about the size of the upper grille, but mine behaved the same as it does now when I had a smaller cooler.  

In reply to rslifkin :

That's exactly the behavior I was seeing on the hills. I suspect having the heater core bypassed was costing me a couple degrees, just from lack of additional radiating surface area even with the interior heat off.

So your 5.9 has the factory hood vents, right? I know that those aren't the biggest actual vent holes, but do you think adding some aftermarket heat extractors would be worthwhile?

Yeah, I've got the factory 5.9 vents.  Cutting up the drip trays for more airflow helped a bit.  I'm planning to cut the hood holes larger at some point and see if that helps more.  If that and the thicker radiator isn't enough to make me happy with the cooling performance, it might get something like a GT500 vent cut into the hood to pull more air through.  

SO I've been reading up on hood venting. My first thought was just to lift the rear edge of the hood, but that seems to work better at slow speeds because of the high pressure area created there at speed. Plus you are dumping hot air into your HVAC intake vent, which could be problematic.

I'm not a fan of the look of the 5.9 vents, plus they're starting to get pricey. I'm thinking I may tape some yarn to the hood and try to identify the l;ow pressure spots at highway speeds, then come up with a venting solution based on where they are. 

It occurs to me that I modified the lower bumper cover and removed some plastic pieces below the sway bar that probably did a lot to manage airflow at speed. I suspect I'll have to mod something to make up for it, but with the aftermarket radiator support it was a necessity.

I haven't had that plastic piece under the sway bar in years either.  I don't remember it looking like it would affect airflow much though.  I might have to experiment a bit with trying to manage airflow down there on mine.  

Is this a V8 thing?  I don't remember ever seeing any temps climbing when I'm towing with my AMC-motored ZJ.  Or it could be 'cause I don't tow things that exceed about 2 tons.

The 4.0s likely cool a bit better due to more open space in the engine bay for air to flow through.  Different fan setups make a difference too (the clutch fans on the 4.0 and 5.2 will do a little better against pressure buildup in the engine bay than the 5.9 e-fan).  

On top of that, it's a speed dependent issue.  Up to 50 mph or so, I can beat on mine as hard as I want with a trailer and it cools fine.  It's only once you get above 50 that it starts to get warmer (the faster you go, the worse the cooling problems get).  

I do also need to test restricting the coolant bypass hose on my Jeep.  The 5.2 / 5.9 can bypass quite a bit of coolant between the bypass hose and the heater loop (the only bypass on a 4.0 is the heater loop).  

Do you think it's worth throwing a block off valve in the heater line since I've bypassed the core? I'm sure the core gives you some kind of resistance in the system, thereby decreasing the flow on that circuit.

EDIT: or something like a ball valve that I could vary the restriction with, anyway.

You may get some benefit depending on the cooling system layout...it can't hurt at least. But from experience I should warn you that anything made of rubber involved in blocking coolant flow completely will fail much faster than usual.

I'm thinking of leaving the heater circuit as-is on mine and gluing a washer (1" OD, probably with a 1/4" or so hole in it) onto the water pump nipple for the bypass hose to restrict flow through there.  

In reply to ultraclyde :

two blocks of wood and a c-clamp....BTDT on the side of the road.

I checked when I got home and i still have the lower radiator trim. Pretty sure this would help create a low pressure spot or at least direct air under the truck. Looks like it will fit and just needs a minor fairing to meet up with the aftermarket radiator support.

If anything, I'd seal off those openings where the lower bumper slots are letting air pass under the radiator support.  That'll probably do more than the small plastic shroud will (as it doesn't hang much below the bumper, IIRC). 

Has it overheated or the transmission overheat light come on ?

 Drive on.

iceracer said:

Has it overheated or the transmission overheat light come on ?

 Drive on.

There is no trans overheat light.  Only indication is that it'll disable OD and force the converter locked in 3rd once the fluid hits 250, but if OD is already off, you'd never notice.  And if it gets to 250+, the trans is almost certainly going to need a rebuild. 

Yeah, a trans temp gauge is on my short list, although I haven't decided if it will be in the pan or on the output line to the cooler. There are arguments for both choices.

It's hard to tell in the photo, but I cut the lower portion of my bumper cover up to the fog light molding. Evn at this cut length, though, the bottom edge is even with the brace under the radiator and there's not really space to lose air flow there. But, because the bumper is trimmed, that black plastic lower piece does hang down enough to be in the airflow. I'll try putting it back on and sealing the leading edge to radiator support, possible extending the fairing up to the bumper cover for good measure. Doesn't look like it will hurt my approach angle off road either. I've got an old sheet metal dryer surround out back for the metal (weren't we just talking about that in another thread?)

it makes sense that a serious off-roading SUV like the Jeep (and my disco) have problems keeping cool at speed. Their hoods are sealed tighter than most to keep the ingress of water into the bay from above to a minimum. Between the sealing of the hood and the raised suspension that 4x4s have, air flow UNDER the truck keeps the air from flowing freely through the radiator and out of the engine compartment. At lower speeds this is not an issue, but once you get going faster, it rears it's ugly head.

I run a "desert spec" thermostat of 75c. Around town, she sits about 81c. Up on the highway, above 70mph, I have seen it creep up to close to 100c, drop back to 65mph, it cools back into the low 90s

^^Thermostats have basically no bearing on the actual running temp. They really only set the minimum temperature of the coolant. You could put in a 195 stat in and you'd still get the same temps on the highway. But you'd also keep a more consistent temp overall.

A lot of engine management systems will significantly richen the air/fuel mix when running below the designed operating temp.

In reply to freetors :

Only ones that are old. Pretty much everything after 1995 will be stoich between 5 and 30 seconds from a start. 

220 would not bother me, as that is the temp the high speed fan turns on. 

freetors said:

^^Thermostats have basically no bearing on the actual running temp. They really only set the minimum temperature of the coolant. You could put in a 195 stat in and you'd still get the same temps on the highway. But you'd also keep a more consistent temp overall.

A lot of engine management systems will significantly richen the air/fuel mix when running below the designed operating temp.

yes and no. I did see a 10 degree drop in running engine temps between the standard thermostat and the "desert spec". I can only assume it is because the radiator on the disco is oversized for it's needs due to the large market area it was distributed to. I think they also used the same radiator in gas and diesel versions