Coolant Temps... Dazed and Confused...

[Mudderoy]

A few years back my 1998 Jeep Cherokee started having problems running hot. About every 3 months I'd notice the operating temp start to rise and I knew it was time to put some water in the radiator.

Leak right? Well I never could find it. A little later I did see some coolant around the freeze plugs. Had them checked and sure enough they were leaking. Had 5 of the 6 replaced. Seems that the one that had the block heater was made of a much better material than the other 5.

I wasn't sure if I knew there were freeze plugs on the back of the block at the time of the replacement or not.

Eventually I was able to drive without over heating issues, but the summer time on the highway I would see heat creep. I started updating the cooling system components, radiator, high flow thermostat/water pump, and heavy duty clutch fan. I even cut a big gapping hole in my hood and put a scoop over it. Still had the highway heat creep issue, but idle, off road, and low speed (below 50 mph) were exceptional even in the near 100 degree high humidity air temps!

Recently I tried an aluminum core radiator and it seems to have resolved my heat creep on the highway issue, at least to a large degree. I have yet to test it in the extreme summer temps, but it is a huge difference.

Recently I had my AW4 rebuilt. While they had the transmission out they saw a freeze plug on the block (normally covered by the transmission) leaking, or weeping. They asked if I wanted it replace. DUH!

After getting the Jeep back and getting the engine temp up to it's operating value, the temp was just a hair below the 210. That's the MAGIC spot!

Prior to this repair I was seeing well below the 210 most of the time at least in the non summer time air temps.

I've been driving around for the last few weeks and it's been sitting there. Gets to that temp pretty quick and stays.

I reasoned that the leaking freeze plug wasn't allowing the pressure to build correctly, or perhaps it was effecting the flow at the back of the block. I just wasn't sure.

Well over the last few days the temp has increase, a little above the 210. Air temps have been a little warmer, but yesterday I saw the needle was well past the 210 mark. This isn't normal.

I was concerned that this gradual climb in temp may indicate a leak. So this morning prior to leaving for work I topped off the radiator. Well that was my intent.

I stood there and stood there waiting for the radiator to fill. I bet I put a gallon of water in the radiator!

You see what I didn't mention was that the fine people at the transmission shop didn't fill up the radiator, well I should say they didn't fill up the cooling system, which included the radiator, block, hoses, etc...

So after they over heated it during the test drive, I filled it up! Since it had been running at the magic 210 number I ASSUMED I had filled it up all the way.

Apparently I had not. Here is my reasoning.

In stead of the coolant temp running at or new the 210 as it had prior to the transmission work (and freeze plug replacement) it was now running WELL BELOW the 210!!!!

Here is a picture I took after getting to work, that's 20 miles in stop and go traffic. Average speed is probably 30 mph, but I would hit 50 to 55 mph during the drive. It only rose to this temp after sitting with the engine running for 5 minutes in the parking garage.
https://lh5.googleusercontent.com/-pUeowKgA-RU/TwS4nMM4pPI/AAAAAAAABlM/djNeFa01ncE/s512/20120104_081245.jpg

While I was driving it never got more than mid way between the midway point, about a needles width lower than shown in this picture!

This is much lower than what I have seen even during the winter last year!

I either have a temp sender/gauge issue, which I do not think that is the case, or something has significantly changed with the replacement of the freeze plug.

I've been trying to wrap my head around what it could be and I'm really having a hard time understanding why a weepy freeze plug on the back of the block would have such a significant change in the cooling system.

Hmmm I guess it is possible that the transmission is now generating less heat and introducing less heat into the cooling system.

I just don't know. I do know this. The heater hasn't been working very well until I get about 1/2 way to work and even then it's a toss up!

[Carves]

Even tho the recovery bottle should sort out the levels after a few warm up/cool down cycles ...................

- The temp sensor is in the heater hose gallery of the thermostat housing.

- The temp sensor needs to be "wet" to function properly ... and the heater core needs hot coolant to function properly ....

So just guessing ... but I'd double check your fluid level in the engine and rad.
12qts is the factory spec ... and a minimum.


The leaking welch plug should ... have caused a slight pressure loss - resulting in a lower boiling point of the 50/50 ... with the end result normally being slightly raised - rather than slightly lower, running temps.

When I got this XJ ... 3 or 4 welch plugs like in the pic had running temps up about 240* and boiling.

http://i1143.photobucket.com/albums/n629/carves-oz/Vehicle%20Bits/Cooling%20Bits/welchplug02front.jpg

A pinhole leak/pressure loss in my rad, caused a 5*f rise in temps a while back .... but I wouldnt have noticed relying on the factory dash gauge ... but the scangauge picked it up.

Have you got a proper temp gauge in addition to that useless dash gauge ???


Given that a dirty/loose CTS connector plug caused me some grief a while back ... a clean of that might be worthwhile too ...


.... and then there is always a sticky or failing thermostat to consider .... especially if its a fail safe thermostat - thats done its job after an overheating incident ... and failed open as intended.

[Mudderoy]

Even tho the recovery bottle should sort out the levels after a few warm up/cool down cycles ...................

- The temp sensor is in the heater hose gallery of the thermostat housing.

- The temp sensor needs to be "wet" to function properly ... and the heater core needs hot coolant to function properly ....

So just guessing ... but I'd double check your fluid level in the engine and rad.
12qts is the factory spec ... and a minimum.


The leaking welch plug should ... have caused a slight pressure loss - resulting in a lower boiling point of the 50/50 ... with the end result normally being slightly raised - rather than slightly lower, running temps.

When I got this XJ ... 3 or 4 welch plugs like in the pic had running temps up about 240* and boiling.

http://i1143.photobucket.com/albums/n629/carves-oz/Vehicle%20Bits/Cooling%20Bits/welchplug02front.jpg

A pinhole leak/pressure loss in my rad, caused a 5*f rise in temps a while back .... but I wouldnt have noticed relying on the factory dash gauge ... but the scangauge picked it up.

Have you got a proper temp gauge in addition to that useless dash gauge ???


Given that a dirty/loose CTS connector plug caused me some grief a while back ... a clean of that might be worthwhile too ...


.... and then there is always a sticky or failing thermostat to consider .... especially if its a fail safe thermostat - thats done its job after an overheating incident ... and failed open as intended.

I have an OBD II scanner that tells me the temp, and the gauge lies. It's about a notch up from and idiot light. Hmmm I have a high flow thermostat in there for a couple of years now. I think I'll order a new one and change it out anyway, just to be safe.

Just ordered a 195 degree Robert Shaw

http://upload.wikimedia.org/wikipedia/en/thumb/e/e4/Robert_Shaw_headshot.jpg/215px-Robert_Shaw_headshot.jpg

Hi-Flow thermostat (2 actually)

[cantab27]

reds jeeps = temp problems.......

[LizardRunner]

You need a VDO temp gauge and sender, they have always been spot on for me (I hear AutoMeter are good gauges too, just no experience with them). Any leak will not allow the pressures to build as intended by the coolant engineers and that will also keep the thermo from operating correctly. It is possible that your new thermo will correct the problem. Lizard runs at a pretty steady 205, takes only 7 minutes to get up to that temp at idle when started at an ambient temp of 27-35 degrees, faster if the ambient is higher than 35. A high flow thermo will cool the block down faster than a standard thermo, but it should also shut off sooner. Also, tonight we got stuck in traffic for around 45 minutes, my temp rose to 210-212 but no higher that whole time.

[bigjim350]

You need a VDO temp gauge and sender, they have always been spot on for me (I hear AutoMeter are good gauges too, just no experience with them). Any leak will not allow the pressures to build as intended by the coolant engineers and that will also keep the thermo from operating correctly. It is possible that your new thermo will correct the problem. Lizard runs at a pretty steady 205, takes only 7 minutes to get up to that temp at idle when started at an ambient temp of 27-35 degrees, faster if the ambient is higher than 35. A high flow thermo will cool the block down faster than a standard thermo, but it should also shut off sooner. Also, tonight we got stuck in traffic for around 45 minutes, my temp rose to 210-212 but no higher that whole time.

In my opinon the autometer guages are just as accurate as the VDO guages at a fraction of the cost. And yes I have used both.

[BlueXJ]

Autometer is a great gauge and can be relied upon to be accurate.

[4.3LXJ]

I have had Autometer and had no complaints.

[Mudderoy]

So going home the running temp was nearly up to the 210 mark, a little more normal. But I guess normal is as normal does. It the morning it's lower. I'm sure it has to do with air temps. It was in the 70's yesterday afternoon.

I see a problem with using multiple measuring devices. It's great if your measuring device is just wrong. When you're building anything you should use one ruler to make all the measurements, failing to do that you may not have things square. The assumption there is all tape measures are the same, sometimes they are not.

I learned the hard way that in my attempt to correct my running hot problem on the highway I changed out the coolant temp sensor. The NEW one read more accurately, however it read higher than the stock one. So my information that I had gathered for the last 9 years (at the time) was now wrong. I thought the changes I was making had made the cooling system run hotter! It wasn't until I put the original OEM temp sensor back in that I started seeing temp values that I was USED to seeing.

[Carves]

So going home the running temp was nearly up to the 210 mark, a little more normal. But I guess normal is as normal does. It the morning it's lower. I'm sure it has to do with air temps. It was in the 70's yesterday afternoon.

Despite windchill being denied by many as a factor ... it is relevant.


I see a problem with using multiple measuring devices. It's great if your measuring device is just wrong. When you're building anything you should use one ruler to make all the measurements, failing to do that you may not have things square. The assumption there is all tape measures are the same, sometimes they are not.

Spirit levels are another ... I always take my good one with me when I go to buy extras/replacements ... as a comparison ... On the presumption my original is correct ... :D

In regards to vehicle temps ... one of the main reasons I like the blingy electronic gauges with the thermo coupling, bolt on probes ... is coz they are so easy to swap around for comparisons/verification.


I learned the hard way that in my attempt to correct my running hot problem on the highway I changed out the coolant temp sensor. The NEW one read more accurately, however it read higher than the stock one. So my information that I had gathered for the last 9 years (at the time) was now wrong. I thought the changes I was making had made the cooling system run hotter! It wasn't until I put the original OEM temp sensor back in that I started seeing temp values that I was USED to seeing.

Yep dodgy CTS resistances ... Still could be worse ...

Heres my 2 years of different driving scenarios / different cooling components - comparison temps of:
coolant, radiator, engine, tranny, underhood, intake air, etc ... in various ambient temps.

Most of which was recorded at 5min intervals ... during minimum, hourly test periods .. and I aint doing all that again ... :bang:

http://i1143.photobucket.com/albums/n629/carves-oz/Tools%20and%20Test/BustedUSBb.jpg

Stooooopid, mongrel, busted USB memory stick .... :mad:

So you'se blokes will have to forgive me if theres a degree or two discrepancy in my comments in various posts ....

Coz Im relying on moments of clarity ... in between bouts of alzheimers ... :rotfl2::rotfl2:

[4.3LXJ]

He was just wanting to digest the data Tony :D

[88on38s]

Here's a ? For yal thay im not sure about at operating temp should my resivoir bottle have so much pressure the it blows coolant out if u barely twist the cap

[Mikentucky72]

So Roy,
How dificult was the replacement of your freeze plugs? I am having to add a gallon a week to my radiator and cannot find the leak! I wonder if I am having the same problem you did. Did you also pull your motor or just the tranny?
Thanky

[Mudderoy]

So Roy,
How dificult was the replacement of your freeze plugs? I am having to add a gallon a week to my radiator and cannot find the leak! I wonder if I am having the same problem you did. Did you also pull your motor or just the tranny?
Thanky

My AW4 was rebuilt. They found the leaking freeze plug when they took out the transmission. So it wasn't difficult for me to replace at all, I just had to pay. :rotfl2: