I was assisted earlier today in replacing my coolant tank. (Thanks!!!)

Problem: STILL getting (intermittent) Engine Coolant Low message. It turns on and off at any given moment. Does not completely stay on... does not completely stay off during any drive, no matter how long I'm driving.

There are MANY threads on resetting the sensor but I'm not 100% clear. Some say it needs to be shorted out when replaced and this will reset it... but I don't know HOW to short it out... so my question is... HOW do I reset the engine coolant sensor. PICS or link to YouTube will be VERY appreciated, if available.

I have a 2005 XJ8 - Vanden Plas

Thank you ALL for your assistant!

 

The tank should come with a new sensor... What you want to do is unplug it, see if the light goes out, if it does good! if it doesn't put a paper clip across the terminals and should go out then, not that complicated. But beware you won't know when you coolant is low!

 

Oh, I see... thanks for the information on shorting it out as a way of "resetting" the sensor.

1. If I short out the sensor (using a paper clip, as in your example), this prevents the message "Engine Coolant Low" from displaying. However, as you pointed out, I won't be able to tell if/when my coolant is low. Is that right?

2. Also, it appears I'm no better off now with the indicator going on and off because it's telling me it's low when it isn't.

If both 1 and 2 are accurate, how will I ever know for sure if/when my vehicle is in danger of overheating?

Are there other options?
Am I overlooking something else can might be causing the false reading. (keeping in mind that the tank is new and that I have confirmed I have no leaks)

Thanks, in advance, to anyone who has time to respond. (I'm so glad I found this forum!) :-)

 

I believe daxter's suggestions were meant as a means of easily diagnosing whether your existing sensor is good or bad, or whether the problem is elsewhere. If your light stays off with the paperclip across the connector, then you need to get a new sensor, which sounds like it comes with a new tank. I would suggest diagnosing and fixing the problem in a timely manner, as until resolved, you may not know when you are truly low on coolant. Running a modern XJ on low coolant for even a short time can be far more catastrophic and costly than doing so with a less sophisticated engine of the past.

 

You have a engine temperature gauge in your dash so you'll know when is over heating. You will also hear the fan running super high like crazy (trust me you'll hear it).

Not all cars have a coolant level sensor so it's not ABSOLUTELY necessary. I mean what I said as both a way of diagnosing it and a work around because I believe you have to get the sensor with a tank, you can't just get the sensor by itself.

In conclusion, you don't need that sensor to know your engine is over heating. Also they should check your coolant every time you service the car (assuming you go to a respectable place or you do it yourself the right way).

 

My coolant level was just as high this morning as when the tank was replaced a couple of days ago and filled with coolant to the fill level.

However, when I started the car this morning, seconds later the "Engine Coolant Low" indicator came on, (thne went off again/on again).... I kept my eyes on my temperature gauge and it went up to the mid-point, as would be expected... but... I drove only 2 miles, round trip on local streets - maximum 40mph), and when I shut the car off after the 2 mile run, the fan kept running "super high like crazy"!!! just as Daxter said it might!

Does this mean I might have a problem aside from a possible bad sensor, since I have plenty of coolant?

This is so confusing. (Before going to a mechanic) is there something else I should be considering.

Daxter/rhankey: I really appreciate your help!

 

From what you have said here I would be testing the temperature sensor and also replacing the thermostat. No way should the fans come on after 2 miles at 40MPH.

Stop driving it and get it sorted before it gets very expensive.

 

I dont follow that either. I would rather know when im low on coolant that a temp gauge. You have no idea if its low and youre ok, or your empty. Those nipples on the toop break all the time and they will empty all the coolant out. And a temp guage sensor reads coolant, not air. Ive seen cooked engines that the customer said it never overheated on the gauge! Why? Because it didnt have coolant in the engine. As far as your fans running on high you may have a air lock in the engine. Did you purge all the air by removing the air bleed in the top of the reservoir by the bleed hose? Fix the car and do not paper clip the pins(sorry dex) that leads to spread pins and poor connections causing further issues

 

With the as yet unexplained intermittent low coolant light and now the fans coming on with even a short drive, you need to assume you do have cooling problem that could cost you an engine if you drive the car any further. Get your car towed to a qualified service place for diagnosis and repair. I guess it is remotely possible you have a few electrical gremlins at play that are coincidentally all giving the illusion of a cooling problem. However, it is sounding like you could have a trapped air pocket in your cooling system, your thermostat is stuck, pump is not pumping, or you have some other problem with your cooling system. Most of these issues are easy to diagnose and cheap to deal with. As Brutal points out, the temp sensor can only accurately measure the temp of coolant, not air. Air pockets do not absorb heat and the pump cannot pump air. Furthermore, the temp guage on the dash is computer managed, and by the time it moves from the mid-point "normal" to high, you may have already done some serious damage to the engine if you were low on coolant.

 

+1. You are playing Russian roulette with your engine. Have it towed to the shop and get all problems related to low coolant and temperature repaired.

 

I hear you all loud and clear and thank you for the wake up call: I will have my vehicle towed to a repair shop. "reputable" being the key word and that's going to be a challenge because I don't know to where I should take it.

Jim: I called the last repair shop I took the Jag to and told them about the fans running super crazy at only 2 miiles at 40mph and the guy said that's normal. So naturally, that shop is out of the question.

Brtual/rhankey/WhiteXKR: Thanks for shedding light on possible issues that could be happening... the last thing I want to do is continue to rely on "luck" that my short errands have not resulted in catastrophe. (so I get the "Russian roulette" statement)

I live in Tampa Florida... does anyone know of a reputable repair shop (anywhere in the Tampa Bay area) or perhaps give me some insight to determine if the shop can be trusted.

Should I get an estimate first and purchase my own parts (one shop wanted to charge me $130 for the coolant tank... I bought one brand new from an auto parts store for only $50.25/free shipping on Ebay)

I don't see the THANK YOU buttons on the end of each of your replies, but please know I am extremely grateful to each of you who have chimed in with your thoughts on the matter. Everyone's time is valuable and I appreciate that you have taken the time to assist! THANK YOU!!!

 

Just want to clarify I agree, I rather have the sensor working right. And I mean with all due respect Brutal because I know you helped a lot of people and I learned a lot from your posts! But I also hate when you go to a forum to ask a question and everybody gives their own opinion and never really answers the question As if I came here and ask how to jump the sensor and everybody said you shouldn't do it, I rather explain and AND THEN give my opinion.

Now back to the problem,

1. Since you drove it for a while I am assuming that the car has no air pockets in the system. But I still wanna ask, did you open the bleed screw to get all the air out?
   
2. Then if the coolant is still full to the top we can assume no leaks. I never changed a temperature sensor in these cars so far, 99.9% of the time it was the stuck thermostat so as somebody suggested before I would go for the thermostat.

Best of luck and Merry Christmas to you all!

 

Dexter... I'm new here but I get what you're saying, and like you, I, too, have been helped by many of the opinions provided by the members!

I'm not a mechanic and have never worked on a car... What I am is a person very willing and determined to TRY to fix anything within the scope of my capability (after plenty of research and advice).... If I feel I'm in over my head I'll seek the services of a professional.

My first and only repair was to replace the coolant tank and I could never have done it without the help from the members of this forum.

So... About that possible air pocket.... Brutal asked earlier if I had removed the air bleed and Dexter just asked if I opened the bleed screw.... Where (exactly) is that located and what/how do I do it? Pics would help tremendously, as I don't know what anything under the hood is or where it's located.... The coolant tank was rather obvious and relatively easy to replace! Is removing the air bleed something that someone with no experience (but with a great deal of determination) can do?

Thanks, again, everyone!

 

(sorry... I meant Daxter... Auto spell check failure)

 

by the way... JaggyZ639 and VZRod639 are the same people... I just noticed that when responded from my android phone, directly from my email notification, it auto-populated my login name from gmail account.

 

JagggyZ,


To be clear, the low coolant warning is less a sensor than a switch. When the warning announces, it's either (1) low coolant, (2) bad switch, or (3) not properly plugged in. Once the situation is corrected, it switches off.


If you continue to drive with the warning and there is a more severe problem (i.e. other sensor inputs out of range), an S/C car will go to restricted performance, and I would hope, eventually turn itself off before melting down. Can't speak to a non-S/C car's desire to live.


As most replacement tanks come with a new switch and you indicated that you just replaced the tank, I'd double-check the plug and then swap back in the original switch if that doesn't clear things up, assuming, of course, that the level is fine.


There is an Engine Coolant Temp code (P0128) that will illuminate the check engine lamp (MIL) that does require resetting. I tripped this one the other day when chasing a small leak. Concurrent with the ECT sensor out of range was full cooling fan operation. Once the ECT was back in range, the fans returned to normal operation, but I still needed to break out the code reader to reset the MIL circuit.


If your coolant level is fine and your fans are screaming, you still have a problem. The flat-bed is the correct response.


Just for the heck of it and because I'm at the keyboard, are you sure the system was properly toped off after the tank was replaced?


Hope this helps.

 

I was just wondering whether there is a bad earth (ground), as this would give an open circuit to the sensor, assuming it works that way.

Just my tuppence

 

The bleed screw is right on top of the tank (If I remember correctly, I'm on vacation until next year so I don't have Jags to go look really quick sorry!). I think there is another bleed screw on supercharged cars.

I attached a pic of the bleed screw on the tank.

Follow these steps:

1. Let the engine run for about 10 minutes
2. With the engine running, use a BIG screw driver and slightly and carefully loosen the bleed screw. Use a big screwdriver on to round it, this is important. Do not take it completely out, just loosen it a little bit until you see bubbles of air and collant coming out.
3. Close it as soon as ONLY COOLANT comes out

It is important that you not take it completely out as you'll make a mess and probably burn your self. All you want to do is loosen it a little bit, enough for bubbles to come out. If I remember correctly (I'm on vacation and I just quitted water for mojitos ), just like 30 seconds of bubbles is the max. Be very careful not to burn yourself.

Then shut the engine off and let it cool. Open the tank and refill. Close the tank and pour some water to clean the excess coolant that came out of the bleed screw. I hope I described this clearly.

 

RCSnyder/Fraser... Flatbed scheduled for Thursday and I'll be sure to casually mention some of your points (along with those of others on this thread) to the mechanic so that they consider the fact that I've been getting feedback from knowledgeable sources... In return, I'm hoping they will be thorough, forthright and honest in their diagnosis and assessment.

Prior to that, I will open the bleed screw in the manner described by Daxter. Thanks Daxter! I appreciate the direct response on that specific question and, yes, you explained it very clearly. I knew by your description what you were taking about but greatly appreciate the pic as confirmation!

Thank you all! -Z

 

.... PS... Enjoy your mojitos, Daxter! Have a great vacation!