[Jerry Bransford]

I towed my pop-up tent trailer up over 8000' from San Diego to Big Bear Lake Friday night and once I hit around 7000' pushing it moderately, all of a sudden the engine lost most of its power so I started looking for a place to pull over. Then within 50' it lost ALL of its power and the Check Engine light started flashing saying Serious Problem, I could barely get pulled over on the narrow mountain road to let traffic get past me.

So I'm looking at the temperature gauge that is just barely above normal. So with that, I figure I've blown the engine.

Then I open the hood and see a small amount of steam and coolant coming out of the radiator cap. Phew, I figure it was just overheated. So after letting it cool, it starts up and runs ok so I drive another half-mile until the same thing happens again. This time I let it cool longer and turn the heater on full blast to help cool the engine. At least the COLD mountain air is helping.

So after making it all the way up and over the 8434' summit, it was fine the rest of the weekend even with lots of slow speed rock crawling.

I've never had an engine that got hot that also caused it to suddenly lose most then all of the power so dramatically without the temp gauge pointer being up near or in the red zone.

Any ideas on why it would do that without the temp gauge being way out of its normal range? At the most on the second power loss it was right in the middle between the normal 210 mark and the red mark.

I'm about to replace the water pump because it's been weaping a bit lately and flush the cooling system and replace it with Zerex G05 HOAT. But the power loss without the temp gauge being that much above normal is puzzling.

Oh, my aux tranny cooler project just got bumped up near the top after the cooling system is finished.

[turtlerace]

First thing I would do is get a second opinion on the engine temperature. Possible gauge issue???

[timberwolf0122]

It might just of been the Tranny overheating, I've experienced the bogging and loss of power going up a mountain in VT and in Canada (long windy road), I think the fluid looses it's ability to drive beyond a certain temp.

[cstevens]

Could your auto tranny have gone into limp mode from heating up? Maybe the additional heat produced by the transmission transferred to the radiator (via the factory tranny cooler) and caused the radiator to heat up which, in turn, would have aggravated/ accelerated the water pump issue....but I would think that you would have seen it via the temp gauge....just throwing out a few thoughts...

[Jerry Bransford]

Originally Posted by timberwolf0122

It might just of been the Tranny overheating, I've experienced the bogging and loss of power going up a mountain in VT and in Canada (long windy road), I think the fluid looses it's ability to drive beyond a certain temp.

I think we have a winner right there. I was thinking transmission cooling issue since the engine wasn't that hot. I'll be installing a tranny cooler asap. I probably need to step up to a fan-driven cooler this time instead of the passive finned aluminum tranny cooler like I installed in my previous TJ. Thanks Timberwolf and Chris!

[turtlerace]

That is a good point Timberwolf. The hot tranny fluid could have been boiling the water in the radiator from heat soak.

[JeffBowser]

Not much help directly, but when I warped my head on the sand dunes that year from overheating, the temp gauge never showed over 210, but man, my clutch was smoking. Ended up having to have the head machined, plus a valve job, in addition to some other things. I figure overheating the tranny baked the oil in the oil pan, too?

[chris142]

Sounds like you have 2 problems. Need to turn the key on then off 3x and read the code that is stored. Probably a trans overheat code.

The Radiator cap should not be steaming even when the engine is hot. Any steam from the cap when the cap is screwed on indicates a bad upper seal. Replace the cap.

[joe_jeep]

it probably was a trans issue as mentioned b4.

on my 97 tj i was slowly losing coolant from the radiator.
i got an air pocket in the cooling system.
my gauge would not read anything. it was like it was cold.
after driving a long time it would get warmer, but never normal.

[Lawrence]

That climb can be brutal with a camper, ask me how I know! Does the transmission fluid smell burnt?

[Night Wolf]

Automatics are awesome!

I had a '96 Lincoln Town Car with the Ford Modular 4.6 SOHC V8. One time it quit running at a stop light and never did that before. Restarting it wouldn't stay running but it was trying to. I was in a busy intersection and not in the best place to be stuck. I could get the engine running by holding the thorttle open while cranking, but then putting it into drive would stall it out - actually had to so a (slight) neutral drop to get moving, and was able to pull into a nearby parking lot.

What I later found out is that the engine did in fact overheat, quite a bit. Yet the temp gauge never went above half, which is where it always stayed. There was no damage to the engine and it continued to operate just fine. I don't remember the specific problem, but it had to do with the coolant not getting circulated. It was overheating around the cylinders, but still normal temp at the temp sensor - hence the gauge didn't change. Once the coolant started flowing, the temp gauge peaked as the hot coolant was now around it.

Temp gauges are misleading for these reasons - it only shows the temp of the coolant at the point of the sensor. No coolant flow, or very little will continue to register as normal. Also, a loss of coolant wouldn't show up (unless in the winter with loss of heat) as the gauge would continue to display what it otherwise would. IMO one of the best things for a vehicle, that oddly a lot of new vehicles lack (just now starting to get though) is a coolant LEVEL sensor. BMW has been using them since the 80s, I remember GM used them on and off too. The 80s BMW used 2 types, one that was in the upper end of the radiator (on cars with expansion tank built into radiator) and also a simple float type switch (for external coolant tank). These cars had pressurized tanks, the Jeep's expansion tank is not. I was thinking of retrofitting one of those sensors, or the low washer fluid sensor (which also uses a float but may be more easy to adapt) to trigger a light inside the Jeep when the expansion tank is very low. This would help warn me of any actual problem before it happens.

As for the '03-'06 gauges - best bet is to pretend they don't even exist. They are all greatly cushioned by the computer. The oil "pressure" gauge is already nothing more than a fancy idiot light. As a test, with the transmission in neutral, engine idling - hold the throttle wide open for two seconds. My engine will bounce off the rev limiter before the tach even reaches 5. Same when accelerating and upshifting fast. The engine will obviously be picking up RPM as you can hear it, the Jeep is acceleration and there is NO clutch slippage... yet the tach is still dropping from the upshift. May not notice it at first but it is there. Think the gauge isn't capable of moving that fast? Put the cluster into diagnostic mode - With ignition off, hold the odo button while turning the key on and watch the gauges move faster then ever.

Which also relates to the temp gauge. I don't put any faith in that thing either. For over a week I drove my Jeep around with no fan clutch, or fan (while troubleshooting the fan clutch). When moving with airflow through the radiator, all was well. Once stopped is where it would get hot after 5+ minutes. During this whole time the temp gauge only managed to move just so slightly beyond center, then out of nowhere it would spike to the red and the check gauges light would come on along with the chime. The thermostat was already open all the way, max coolant was circulating, but it is simply not a direct reading gauge. Turning the heat on high/max was enough to pull the coolant temp back down to safe levels.

In short: Just because the temp gauge stays at center doesn't mean the engine is not running hot, or even overheating. It simply means the computer thinks the engine is operating at "normal" range of temp, and the gauge will display it as such.

A true, direct reading temp gauge will fluctuate a good bit under different driving conditions as the coolant cycles through warmer/cooler periods. I had a '94 Isuzu truck, that as well as all 3 of my 80s era BMW's had/have a factory/stock direct reading temp gauge. Normal operating was around 1/3, not nicely in the center... but the big differences are when stopped or in traffic it would climb just a bit and I could hear the fan clutch engage. Once the vehicle started moving again (or RPM was increased to flow more air through radiator) the gauge would dip back down to normal. Even when shut down when hot, as the coolant/underhood temp increases for a few minutes, if the ignition was turned on - the gauge would display the higher temp, once the engine was started and coolant circulated, temp went back down.

Summary: the late model TJ gauges are worthless. About the only thing accurate (if adjusted properly) is the speedometer. Which is why I'll be installing atleast a real oil pressure gauge and maybe one or two others.

[hustler905]

^ How about a Scangauge and you can instantaneously see whatever you want (except for coolant level).

[robncar]

Originally Posted by chris142

Sounds like you have 2 problems. Need to turn the key on then off 3x and read the code that is stored. Probably a trans overheat code...

If I recall correctly that's not how the late model codes work. The powertrain codes are stored apart from other trouble codes and require a DRBIII scan tool to read. There would be a generic powertrain code that may be displayed but it's non-specific. It tells you that a powertrain code has been set but that's all.

Sent from my DROID2 using JeepForum

[Night Wolf]

I have thought about that, and probably will get one.

However it will not tell you oil pressure, as there is no actual oil pressure sender on the engine (just a switch)

I also wonder how accurate the coolant temp would be, if it would rear direct from the sensor, or (most likely) after being buffered by the computer.

I plan to add a real, direct oil pressure gauge and a vacuum gauge. I was thinking about adding oil temp, but for the intent of oil temp on the Jeep, I'll be able to tell that via the direct reading pressure gauge (one of the many benefits of having one)

[hustler905]

My coolant temp seems pretty accurate, I am basing that on seeing it warm up on very cold winter starts.

I also had a BMW with a coolant level sensor, it was great to know - especially because the cooling system in E39's blew up with alarming regularity.