Cold weather mileage - discussion

[cruiser54]

Those of us who have eliminated the heater control valve. I'm assuming since it always runs through the heatercore, that we are going to experience decreased mileage?

No. Why would we?

 

[WB9YZU]

Tom, 150 is too low. Aaron tells me it's been mighty cold out there so far.

If you have over done it in the cooling dept, hard to believe in an XJ, partially block the radiator as recommended. That works for me when it gets real cold here, or on long hwy trips (note to self: add cardboard to XJ before it gets really sh8tty).

I would also revisit that T-Stat, I have had new ones fail out of box.

As far as additives, Gasohol (10%) has enough alcohol in it already to prevent water in the fuel from becoming an issue. For those who hate running Gasohol. add a bottle of Isopropyl based heat (I forget which color bottle that is).

Also, as a general rule, gas mileage tends to take a dive in the Winter. Some say it's "Winter Gas", others, excessive idling. Me? I think that the viscosity of lubricants in the drivetrain and wheels, combine with increased rolling resistance due to lower tire pressures and snow, and the engine taking longer to reach optimum temperature to put the suck on any hopes of having reasonable gas mileage.

 

[2X_01_Jeeps]

150 is too low. First question is whether the engine is really at temp and the gage is low or whether the gage is right.

IR thermometer should prove that.


If it's really running at 150 then it's probably a defective thermostat. Even if the heater core is getting full flow and running blower on full high, the 85 mph speed produces enough heat to need a little flow thru the thermostat for cooling.

Running at 150 should kill mileage and could hurt other things too with condensation in the oil and excessively rich mixture going to the cat for long periods.

Wave when you pass me! (and you probably do if you're running 85)

 

[Ecomike]

If he isn't getting heat and the temp is staying around 150 when running, the issue is in the cooling system. The Oxygen sensor is not and cannot keep the engine temp at 150. Even with a failed Oxygen sensor, my rig had no issues staying hot. Bad fuel mileage and idled poorly yes, but the heat was fine.

Fix the cooling system issue first.

My 87 Renix operating temperature increased by 45 F when I replaced the dead O2 sensor, and the gas mileage doubled, so don't give me that nonsense. I know what I am talking about. With out a working O2 sensor/closed loop operation the ECU runs the engine rich, open loop, which generates a lot less heat. Closed loop it runs leaner, and thus hotter. Also the heater core in 0 F weather acts like a radiator to cool the coolant, and if the vent door is not sealing, and outside 0 F air is being brought in to be heated, it will cool the cooling system coolant down because the heater coolant lines to the heater core BYPASS the thermostat!! SO the damper door on the inside air versus outside air vent door (what ever it is called), needs to be checked to see if it is letting in cold outside air or not!!!! It is operated by a vacuum valve near the passenger door just under the knee kick panel (dash). Third, moving at highway speeds the block gets more cooling directly with 0 F ambient temps. Add the three together and you freeze! LOL, Ask me how I know!!!:laugh:

 

[Ecomike]

I agree to fix the cooling system first.

But, I think you're misunderstanding Ecomike. He's saying it is going into closed loop even at 150* but that the oxygen sensor is the cause of the poor mileage.

I'm not sure I agree. The only way I'll find out is to hook up my DRB-II and monitor the system from start up and see what temp it goes into closed loop at.

That is not what I said. I said IF the O2 sensor / ECU package is working properly, it goes closed loop about 10 seconds after the engine starts, no matter how cold the engine is!!!!! Or at least it does for an ambient cold start up around 70 F!!!! Several of us have verified this!!!

Then what I said is the terrible mileage and cold engine together make it very likely that the O2 sensor / wiring / O2 sensor heater power ... some part of O2 circuit, is not working, and that the ECU is stuck running open loop, rich and thus the engine runs a lot cooler. Then add on the ambient 0 F, plus the heater core acting like a radiator (bypassing the thermostat) and you get what he has, 150 F coolant.

 

[Ecomike]

I agree to fix the cooling system first.

But, I think you're misunderstanding Ecomike. He's saying it is going into closed loop even at 150* but that the oxygen sensor is the cause of the poor mileage.

I'm not sure I agree. The only way I'll find out is to hook up my DRB-II and monitor the system from start up and see what temp it goes into closed loop at.

DRB-II is not needed. When it is open loop the O2 sensor reads rich, (IIRC about 4 volts steady state), when the ECU goes to closed loop, the O2 sensor voltage at idle swings rapidly back and forth from about 1.5 to about 3.5 Volts, about once per second. This can be read directly off the O2 sensor (in parallel, back probing the connecting sensor connection while the engine is running) with a high impedance analog volt meter.

 

[Ecomike]

I'm not so sure that the thermostat is that bad. I think that running the heater at full blast when it is below zero provides enough cooling to keep the temps down, even if the thermostat is pretty much closed. You would be surprised how much heat a heater core can dissapate.

The next time you are on the trail and you are overheating, turn on the heater full blast and watch the temp drop like a rock.

EXACTLY!!!!! X2!!!!

 

[MNgopher]

I'll stand by my decades of cold weather experience with this setup and others. If the engine is running freeway speeds (think I noted a reported speed of 85 mph), it will generate plenty of heat even with the heater running full blast to keep the engine coolant temp at 190ish, regardless of whether it is operating in open or closed loop, provided the thermostat is operating correctly.

 

[cruiser54]

I'll stand by my decades of cold weather experience with this setup and others. If the engine is running freeway speeds (think I noted a reported speed of 85 mph), it will generate plenty of heat even with the heater running full blast to keep the engine coolant temp at 190ish, regardless of whether it is operating in open or closed loop, provided the thermostat is operating correctly.

I agree. A thermostat has no knowledge of air fuel ratios and will hold enough heat in the engine til it reaches it's opening temp regardless of whether the heater is on or not.

 

[Ecomike]

Then why do diesel truckers block huge parts of their radiators in the coldest parts of winter on the highways?

 

[cruiser54]

I used to own big diesel trucks, a fleet of them, and we didn't block the radiators. Keep in mind that the truckers also run turbocharged engines therefore have a HUGE cooling system to handle the heat for forced induction for the hot days. Our XJs do not have that oversized cooling system. If anything we have an undersized cooling system.

 

[cruiser54]

Had a thought. Why doesn't EVERYONE, especially those with bad oxygen sensors, who lives in a cold climate have this over-cooling issue in their XJs? I don't and I see 0 to teens all through the winter. Have a good oxygen sensor now but didn't last winter.

 

[Ecomike]

I have seen them with covers over the radiators. May have been way back in the day, 60's, 70's, or on trips I made way up north in the winters, not sure, but I have seen them use them. Not sure of all the reasons why.

I had two extreme cases that had nothing to do with the thermostat. One was a 73 Ford LTD. It ran too cold. One winter night I popped the hood and the Exh manifold was cherry red. The Vacuum advance on the Dizzy was rusted, locked up, so the only thing that got hot was the Exh manifold!!!!

My 76 Dodge charger, SE, 400, 4 barrel, gas hog, "lean burn" (one year special that had no cat converter, failed experiment) ran so hot it cooked everything in the neighborhood, no mater how much I beefed up the cooling system. Cooked :flame:the Transmission as well, 7 times in 2 years! I ran the radiator(s) on it at 20 psi!!!! I finally gave up on that Chrysler experiment after just 4 years. I had replaced the fan and fan clutch on it with a HD SS DD flex fan even. The problem was it ran "TOO LEAN"!!!

 

[Ecomike]

Had a thought. Why doesn't EVERYONE, especially those with bad oxygen sensors, who lives in a cold climate have this over-cooling issue in their XJs? I don't and I see 0 to teens all through the winter. Have a good oxygen sensor now but didn't last winter.

Just because it is running rich, does not mean it will run cold. Lots of ways for it to run hot, and run rich with a bad O2 sensor. An exhaust leak blowing on the block, poor flow through the radiator, bad fan clutch, worn water pump, clogging radiator, and so on. I see hoards of posts here each winter from complaints their jeep heat is not working and the cooling system is running too cold.

In the 40 years, I have never had a bad thermostat!!!!!

 

[cruiser54]

Too lean and the difference between a working and non-working oxygen sensor are 2 different things. A working oxygen sensor does not make a Jeep run overly lean, nor does a non-working oxygen sensor make it run so rich that it runs cool.

 

[cruiser54]

I just had 2 Stant super-stats go bad on me in the same Jeep. You must be truly blessed and/or haven't replaced one in many years. I replaced the second one with a factory stat that has the "jiggle valve" and now the heater is satisfactory. I tested the hoses with my laser temp sensor before and after BTW to verify.

 

[Ecomike]

I just had 2 Stant super-stats go bad on me in the same Jeep. You must be truly blessed and/or haven't replaced one in many years. I replaced the second one with a factory stat that has the "jiggle valve" and now the heater is satisfactory. I tested the hoses with my laser temp sensor before and after BTW to verify.

I have replaced maybe 8-10 thermostats, but the old ones were not bad after all when I got them out, or I replaced them while I was doing other replacement work. I only replaced them to try and solve overheating problems, or because I was replacing a head, or water pump, etc. I do replace hoses, caps, antifreeze fan clutches, ....more frequently, but the replacement thermostats never solved any problems I had. They made no difference. None were ever failed open, and all still opened in a boiling pot of water.

 

[Ecomike]

Too lean and the difference between a working and non-working oxygen sensor are 2 different things. A working oxygen sensor does not make a Jeep run overly lean, nor does a non-working oxygen sensor make it run so rich that it runs cool.

I will say it again, I have measured a good 30 F plus difference in the operating temperature of my 87 and 89 by disconnecting the O2 sensor. Perhaps it is more noticeable in mine since I have used 160 and 180 F T-stats. I have not used anything over 180 F for a T-stat in 40 years either.

It will be real interesting to see what our OP turns up.

 

[MNgopher]

Kinda figured the diesel question would be raised. Yes, you do still see some diesels using winter fronts in cold climates, such as where I live. And yes, they do serve a purpose. Diesels, from a heat generation perspective, are more efficient at using their heat as part of the power producing process. They can also generate a ton of heat when working hard. As a result, many diesel systems are on the overcooled side of things. In addition, depending on the application, diesels typically will generate very little heat at idle, so the winter fronts help with that situation as well.

I think we can all agree the Cherokee is on the undersized side of things in the cooling realm. Of the gas vehicles I've driven, the XJ has never been accused of poor heating.

As far as bad thermostats, I've never seen so many bad ones as in recent years. For whatever reason, it seems like the ones the Jeeps take are particularly prone to it. My previous replacement took three thermostats to get one that worked right (two cheap parts store branded ones then a $15 dollar one from the dealer solved it).

 

[Ecomike]

Kinda figured the diesel question would be raised. Yes, you do still see some diesels using winter fronts in cold climates, such as where I live. And yes, they do serve a purpose. Diesels, from a heat generation perspective, are more efficient at using their heat as part of the power producing process. They can also generate a ton of heat when working hard. As a result, many diesel systems are on the overcooled side of things. In addition, depending on the application, diesels typically will generate very little heat at idle, so the winter fronts help with that situation as well.

I think we can all agree the Cherokee is on the undersized side of things in the cooling realm. Of the gas vehicles I've driven, the XJ has never been accused of poor heating.

As far as bad thermostats, I've never seen so many bad ones as in recent years. For whatever reason, it seems like the ones the Jeeps take are particularly prone to it. My previous replacement took three thermostats to get one that worked right (two cheap parts store branded ones then a $15 dollar one from the dealer solved it).

Well we have all seen a big increase in bad brand new parts lately (CPS and IAC most recently for me), that is for sure. I wonder if the winter extreme temps damage them? It never really gets below 25 F for more than a few hours here in Houston. And I am so anal about maintaining my cooling systems since I had that 76 Dodge lean burn heat engine (LOL), I have never had an engine overheat (and thus damage a T-stat) from a failed cooling system (except one recently), and that was not caused by the T-stat, it was loose clamp on a cheap disposable plastic radiator that popped off while on the freeway (lower hose, all coolant lost in seconds...), LOL.

So are the new ones failing open, or closed?