Overheating and already replaced all the usual suspects

So I was overheating a bit on the way back from a mojave trip. I went to work learning and replacing everything to fix the problem.

The list of new parts as follows:

radiator - champion 2 row aluminum (comes with new radiator cap)
lower radiator hose - from dealer and has the spring inside
tstat - napa, higher end 195 (i think stanton)
water pump - napa
fan clutch - napa
b&m trans cooler in front of the mechanical fan side, bypassing the radiator.

I cleaned the ac condenser grill, picked out every rock, used a grinded down hacksaw blade and fixed every fin then used some engine degreaser and hosed down from the engine side out.
I verified the electric fan was working (turned on ac and fan was spinning)

I tested it going to work. Everything looked fine then I overheated on the way back, it was hot outside and I had the ac on and I was going about 65mph. I don't overheat around city speeds.

I have 31s with 3.55 ratio if that makes a difference.

I'm not sure what tests to do next and could use some suggestions.

Thanks,
Eric

First few things I would do, is one, ohm test the temperature sensor. I'm guessing we are talking about your 98, I don't have an ohm temperature chart for that year, you may have to go google. I don't trust senders or gauges. Clean the temperature sender plug with very hot water, dry it, then spray it out with contact spray.

Does the aux fan come on when the motor overheats?

Second thing I'd do is use a marker and mark the coolant level in the coolant recovery bottle with the motor stone cold, early morning is best. Then keep a close eye on it. Check it often, when the motor is cold.

Third thing is, on a cold motor, put a catch pan under the front, remove the radiator cap and start the engine. It will likely overflow a bit. While working the throttle from the front, rev it slowly (it will likely spew a bit), the technique is to let it spew but not so much and so quickly, that the moving parts spread it all over the place. Coolant isn't good for electrical connectors or even alternators (that is why you cleaned the temperature sender connector ). As the motor heats up to operating temperature look for bubbles coming to the top of the open radiator filler neck. A constant 1500-2000 RPM's works better than blipping the throttle, it keeps the coolant in the radiator filler neck at a constant level and makes the bubbles, if there are any, easier to see. It may take awhile for any bubbles to make it to the top, at least ten minutes.

When you are finished, let the motor cool some, then pour some clean water over the area covered with coolant.

Yeah, like 8Mud said...is the sensor sending accurate info? What indications do you have of overheating besides a temp gauge reading that is high?

In another thread a guy did everything and finally put a stock radiator back in and that solved his problem.

LOFL. Can you link to that thread? It would be advantageous for members to know what freaking aftermarket crap that was.

Thanks for the suggestion, your right that I need another method to verify the temperature. I am only going off the temperature gauge and indicator light.

I did replace the sender with an autozone one before I ever had any overheating issues and its pretty new, maybe i should get another one. I've been preferring napa parts lately anyways. When you say checking the ohms and a temperature chart. Are you talking about bypassing the temperature gauge and reading the temperature by monitoring the resistance of the sender. If that's the case then is it safe to assume the temperature sender is a thermistor and not a thermocouple so I can just wire in a multimeter and watch it as I drive? That sounds reasonable and easy.

Are there any suggestions for another good way to directly monitor temperature as I drive that would be independent of the temp sender and gauge? That way I can use 2 readings to compare.

When I put everything back together I had ordered a serpentine belt gauge as I definitely can't calibrate by feel regardless of twisting the belt 90 degrees or measuring deflection and this was proved yesterday when I got the gauge. I found that I was previously way below 100lbs which is the min that the gauge can read, I'll guess I was somewhere around 60lbs. so I got it up to spec at 140-150lbs. I went for a test drive and it didn't overheat but that was at night, though the temperature according to gauge reaching about 220. Is it at all possible the pulley of the water pump was slipping and that It didn't make any screeching noise?

Also interestingly enough, my heater isn't putting out very much heat like before. This had previously happened and a heater core backflush fixed it, but why now? again and especially with all the parts having just been replaced, it just seems a little too coincidental.

My next step is to bleed the system again, I have one of those cool funnels that attaches to the radiator.

Also I'm going to change the trans cooler plumbing, right now it's just like: http://jeepin.com/features/trannycooler
however, b&m recommends the inlet at the bottom of the cooler which is opposite of what the jeepin writeup has.

I'm also going to be trying to figure out a better way to verify temperature more accurately and I'll draw a line on the cooler bottle after I bleed and have a couple of cold heat cycles to purge air.

If those don't help I think my next test will be some fsm troubleshooting advice of removing the tstat and upper radiator hose, serpentine belt off the water pump, fill with coolant up to 1/4 inch the top of tstate housing and watch for bubble as I rev to 3k rpms 3 times.

Thanks for all the help everyone! I really have been reading other threads and trying to save us all from another overheating thread but I'm hitting the frustration point of self diagnosing and learning on this subject and need some "hand holding" haha =) On the bright side, when I started all this I didn't even know how the cooling system worked. I really hope this isn't a cracked/warped head blown head gasket or worse. My skill level isn't up to those problems yet.

Thanks,
Eric

I replaced a temp sender once, before I knew there were two possibilities. The kids at Autozone didn't even ask which I needed, so they just gave me one. Turns out they gave me the one for the gauges and this caused my temp light to glow and made me think I was running hot. I even ended up paying $80 to have Christian Bros look at it, and they found nothing wrong. Once I found out there was more than one sensor I switched them and everything was fine.

What year is your Jeep? 97+, there is only one sensor, and the PCM drives the gauge based on that sensor reading. I use a multimeter and an IR thermometer with the Jeep warmed up, but turned off. As the temp falls, the resistance of the sensor should increase. It takes a while, but unplugging the CTS and driving (again, on a late model) will run the aux fan constantly, throw a CEL, and probably cause the Jeep to run poorly.

Here's the chart to test the CTS.

http://s266.photobucket.com/user/AHhub/media/forum stuff/Resistancetable.png.html

I bought an aftermarket CTS a while back; it was off by close to 30*. I would buy Mopar or the best that NAPA had, assuming it wasn't an SMP or BWD brand, but only if I could confirm my issue was a sensor.

If you unplug the CTS the engine will probably not even idle without manually pressing the throttle.

I seen the the start of your list of parts and stopped reading it. Have you talked to or been to a radiator shop? How much crap came out of the motor when you did the back flush on it?

scottmcneal said:

I seen the the start of your list of parts and stopped reading it. Have you talked to or been to a radiator shop? How much crap came out of the motor when you did the back flush on it?

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It's a 98 btw.

I had done a backflush about a month prior to the new cooling parts. Alot of brown came out, I emptied many 5 gallon buckets, with about the first 5 of the buckets filled were very brown. This is a used 100k vehicle I bought with a neglected cooling system. It was also in a front collision that had been "fixed" but when I replaced the radiator I noticed the one I pulled out was actually bent a bit, so I don't mind starting with new cooling components.

What about my list made you stop reading?

Sounded like you was just throwing parts at it. But if you get did a lot of thick crap out of it, you should take it in to be flushed at a shop.Had to do this to mine.The water jacks was plugged i guess, because when they gave it back to me it ran at 190 while the AC was on.I live in the desert, we hit above 100 every day during the summer. Rust kills everything in a cooling system i think.

Sorry for not reading your complete write up.

Yeah for sure I threw parts at it. Every time I did a search for how to test a fan clutch or water pump I read "there's no good way". Also the original radiator hose when I got the jeep didn't have a spring and was pretty squishy so I thought it could have been a crappy aftermarket hose sucking close. But my initial overheating problems sounded like radiator because the overheating was only at highway speeds. The tstat was only $5 and if I'm going to do that I might as well change the waterpump which was like $40.

I expected everything to be just perfect afterwards and oh well, I was wrong =) Now I'll start following this threads recommendations. Right now I'm researching and trying to figure out how to do a leakdown test as that seems to be a good direction to go in.

Is it safe to assume that there's only an engine issue if I lose coolant from the recovery bottle?

That or the heater core has a small leak in it.

First things first. Make sure you really have a problem before you fix it. With the money you've already thrown at it, an infrared thermometer would be a cheap toy to have. You didn't even say that it was boiling over. If it doesn't boil over, you don't really have a problem. Except maybe the temp gage.

winterbeater said:

First things first. Make sure you really have a problem before you fix it. With the money you've already thrown at it, an infrared thermometer would be a cheap toy to have. You didn't even say that it was boiling over. If it doesn't boil over, you don't really have a problem. Except maybe the temp gage.

Click to expand...

Your right, thanks. I'll get back when I get some more info

Yeah man I almost did what you did. I even started spending money, only to find out the indication that I was hot was a lie. Seriously, go get a new sensor that is specific to your gauge and see what happens before you do anything else.

There is not a separate sender for the gauge for 97+. The PCM handles engine management, fan operation, and driving the gauge based on the reading from the CTS in the thermostat housing.

Oh my bad. Wait..someone said that already too, didn't they? Soooorrry!!!