1974CJ5 Posted January 28, 2009 Share Posted January 28, 2009 This situation happened to me a couple weeks ago: I am driving to town, about a 20 min. drive and I notice my temp. light is on (seeing as that is all my truck has is a light no gauge which is just freaking sweet ::dripping with sarcasm:: .) I quickly pull into a parking lot; turn it off, pop the hood, and jump out. I am looking in the reservoir (which is full) and looking for steam and using my "skin thermometer" (my hand) to see if the engine felt or looked hot, no perceivable problems. I know the thermostat was open because I was getting heat from the heater. I am a hot coolant coward since I poured 5 gallons of water on my arm that was past it boiling point before in my life, and so far that is the most pain I have ever felt, you skin falls off over the course of a week, leaving what looks like a thin white membrane covering your muscles... gross painful not going there again! So I decided, well I will limp it home and watch for steam. Well the light would come on for a few seconds and then go out, and repeated all the way home. So I get it home and still no signs of overheating, my dad who has no fear of anything except lightening (this is not me bragging about him either, he's one of those people that has only survived this long because his guardian angel is apparently really really on top of things, and you don't want to be too close to him no matter what he is working on.) He just grabs a rag and pops the radiator cap off which its still at whatever temperature it was 2 minutes after I shut it off. I am partly expecting coolant to come out like old faithful, but it didn't it just come out under normal pressure. At which time my dad had it all over his hand, and said "Nope, I't aint hot." And ever since he took the cap off under pressure the light has never come on again, any ideas as to why this is? Link to comment Share on other sites More sharing options...
maddzz1 Posted January 28, 2009 Share Posted January 28, 2009 Maybe the temp sensor is going bad. Link to comment Share on other sites More sharing options...
Pete M Posted January 29, 2009 Share Posted January 29, 2009 Technically it's a "switch" rather than a sensor, but it definitely could be faulty either way. Or corrosion is screwing with the electrical signal. Might be time to think about upgrading the the full cluster with gauges? :brows: Link to comment Share on other sites More sharing options...
garmj Posted January 29, 2009 Share Posted January 29, 2009 Just because your heater is working doesnt mean your thermostat is working, it only controls waterflow to the radiator not the heater core. There is no substitutefor a real temp gage. Link to comment Share on other sites More sharing options...
Eagle Posted January 29, 2009 Share Posted January 29, 2009 There is no way your father, any other mortal human, or even Superman could open a radiator cap of a vehicle at operating temperature and properly filled, and not have a LOT of very hot coolant come spewing out. My guess is that your coolant level was so low that the coolant was overheated, but because of the amount of coolant (not) in the system, there was an air pocket in the head where the sensor is and it was "seeing" coolant only sporadically. What year MJ and what engine? It would help to know what kind of cooling system your truck has. Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 29, 2009 Author Share Posted January 29, 2009 There is no way your father, any other mortal human, or even Superman could open a radiator cap of a vehicle at operating temperature and properly filled, and not have a LOT of very hot coolant come spewing out. My guess is that your coolant level was so low that the coolant was overheated, but because of the amount of coolant (not) in the system, there was an air pocket in the head where the sensor is and it was "seeing" coolant only sporadically. What year MJ and what engine? It would help to know what kind of cooling system your truck has. Well holy crap I must of witnessed a miracle! Like a statue of Mary crying blood! Your guess is wrong the radiator was full even after what little bit (now when I say little bit, I mean not geyser like, but the expected amount) came spewing out. The quote "It aint hot" was his way of saying the engine wasn't hot. The coolant was quite hot, but not steaming, shooting radiator cap into orbit hot. It is a 1987 with a 2.5. Unless of course no one, not even superman, could own a truck manufactured in 1987 with a 2.5 in it. Anyways, Are there any write ups on switching to the full cluster with gauges? Also so I am assuming that the fact that the overheat light comes on when the key is turned to the on position (not after starting) is only verification that the light bulb in the dash still works, no verification on the actual switch correct? Link to comment Share on other sites More sharing options...
MJ300 Posted January 29, 2009 Share Posted January 29, 2009 The full gauges are a very easy swap to do speaking from my own experience. Its basically a plug and play operation that does not take much mechanical knowledge at all. http://www.naxja.org/forum/showthread.php?t=921205 This write up really really helped too. :cheers: Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 29, 2009 Author Share Posted January 29, 2009 That is a great write up!! Thanks man! In another post some guys where telling me how plug and play these things are, but I didn't think they were to that extent, The tach even works without modification! New project for this weekend! Link to comment Share on other sites More sharing options...
BLHTAZ Posted January 29, 2009 Share Posted January 29, 2009 You need to be sure that you get a cluster from the same era and engine size or it will not be a simple plug & play situation. If you get one from a 4.0L there will be calibrations that have to be done for it to work properly. Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 29, 2009 Author Share Posted January 29, 2009 Thanks for the heads up, on that I will begin my search... Would the rest of the drivetrain make a difference? For instance: Mine is a 1987 2.5 w/ ax4 and 3.55 gears So if I got one out of a say 88 2.5 w/ax5 (or an automatic even) and 4.10 gears would that still be compatible? Or should I wait until I find all the stuff I am going to do for my drivetrain swap? Which I will be driving it for a while before the perfect donor vehicle for the perfect price is located I am sure. :doh: Or is the only dash available for a 2.5 xj or mj of that era going to be the idiot light type like the one I already have? Link to comment Share on other sites More sharing options...
BLHTAZ Posted January 29, 2009 Share Posted January 29, 2009 The engine is the only concern as the tach will be the problem. I have been told, and have seen on here, that the calibration of the tach from a 4.0L to the 2.5L 9or vice versa) is not terribly difficult if you get the right cluster to be calibrated, but it would be a lot less headache to just get the right one and not have to worry about it. Link to comment Share on other sites More sharing options...
Eagle Posted January 29, 2009 Share Posted January 29, 2009 Well holy crap I must of witnessed a miracle! Like a statue of Mary crying blood! Your guess is wrong the radiator was full even after what little bit (now when I say little bit, I mean not geyser like, but the expected amount) came spewing out. The quote "It aint hot" was his way of saying the engine wasn't hot. The coolant was quite hot, but not steaming, shooting radiator cap into orbit hot. It is a 1987 with a 2.5. Unless of course no one, not even superman, could own a truck manufactured in 1987 with a 2.5 in it. Anyways, Are there any write ups on switching to the full cluster with gauges? Also so I am assuming that the fact that the overheat light comes on when the key is turned to the on position (not after starting) is only verification that the light bulb in the dash still works, no verification on the actual switch correct? Look, Mate. Sarcasm is not appreciated when we are trying to help you with YOUR problem. If you don't want help, stay off the computer and figure it out by yourself. If the engine / cooling system was hot enough to turn on the light, or even hot enough to be at normal operating temperature, removing the radiator cap WOULD have resulted in a geyser, the radiator cap being launched, and your father getting scalded. The temperature of the system runs around 210 degrees or so. Human skin gets scalded at temperatures over about 110 or 120 degrees. If it didn't blow up when your father removed the cap, it wasn't up to temperature, and thus definitely should not have been blinking the light on and off. If your radiator was full but not getting hot, is it possible it was frozen? What was the air temperature, and what temperature is your anti-freeze good for? Also, is it possible that your water pump isn't pumping? Or that your thermostat is stuck, either closed or partially closed? Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 29, 2009 Author Share Posted January 29, 2009 Um, okay, it's not my intention to get in a pi$$ing match with you, but don't insinuate that my post is BS! and expect me to not retaliate! If you truly are trying to help, I really appreciate it, and with the assumption that you are really only trying to help; here is the information: "If the engine / cooling system was hot enough to turn on the light, or even hot enough to be at normal operating temperature, removing the radiator cap WOULD have resulted in a geyser, the radiator cap being launched, and your father getting scalded." Well that just didn't happen. After a 40 min round trip drive with only about 10 minutes to cool down after the first 20 minutes, and then an additional maybe 2 minutes of cool down before the radiator cap was popped, I don't see much chance of cool down. Plus a thick rag does wonders on saving you from getting scalded when removing a radiator cap. "If your radiator was full but not getting hot, is it possible it was frozen?" What was the air temperature, and what temperature is your anti-freeze good for? No not frozen, the coolant tested at -40 degrees taken with a tester. The temperature that day was 10 degrees Fahrenheit (which could result in a cool down faster than average, but not enough to significantly lower pressure in that amount of time I wouldn't think. Also, is it possible that your water pump isn't pumping? Or that your thermostat is stuck, either closed or partially closed? This could be possible, but I don't think it would be very likely since I have driven it everyday since, and no overheating has occurred. Link to comment Share on other sites More sharing options...
shelbyluvv Posted January 29, 2009 Share Posted January 29, 2009 My 86 2.5 used to play games with the light all the time. It turned out to be a bad temp sender. And fellas, lets keep it nice. Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 29, 2009 Author Share Posted January 29, 2009 And fellas, lets keep it nice. :agree: I apologize for the sarcasm, the post just hit me the wrong way on a couple points. One of the things that I really like about this forum is that there isn't much back and forth trash talking, (look on a honda forum yeesh!) I don't want to be viewed as trying to be like one of those people, so I do apologize. Back to the issue, I think the possibility of the temp sender (switch or whatever you want to call it) being bad is probably very likely. I need to check that before I move on to anything else (it's not getting hot now, but I don't want it to not be working and it really get hot.) Can this be checked with an ohmmeter? Link to comment Share on other sites More sharing options...
maddzz1 Posted January 29, 2009 Share Posted January 29, 2009 And fellas, lets keep it nice. :agree: I apologize for the sarcasm, the post just hit me the wrong way on a couple points. One of the things that I really like about this forum is that there isn't much back and forth trash talking, (look on a honda forum yeesh!) I don't want to be viewed as trying to be like one of those people, so I do apologize. Back to the issue, I think the possibility of the temp sender (switch or whatever you want to call it) being bad is probably very likely. I need to check that before I move on to anything else (it's not getting hot now, but I don't want it to not be working and it really get hot.) Can this be checked with an ohmmeter? If you are seriously considering swapping your cluster to gauges then you will need to swap your temp and oil pressure sensor anyway. So rather than buy a new one (i know they arent much), I would put a post in the classifieds for a cluster and just get the new ones for the gauges. Is there a way to test the temp of the coolant in the radiator and in the block to see if they are different temps? The thermostat may be sticking and opening up later than it should allowing the coolant in the engine to reach a higher temp Link to comment Share on other sites More sharing options...
1974CJ5 Posted January 29, 2009 Author Share Posted January 29, 2009 maddzz1 that is a good idea about the classifieds section, I always freakin forget that there is even a classifieds section on this forum., I will do that if my already planned trip to pullapart this weekend turns up no results. Link to comment Share on other sites More sharing options...
Eagle Posted January 29, 2009 Share Posted January 29, 2009 Can this be checked with an ohmmeter? Nope. It's not a variable resistor, like the sender for the gauges. It's an ON-OFF switch. The only way to test it is to connect a small battery and test light to it, and suspend the sensor tip in a pan of water on the stove. Use a candy thermometor to monitor the water temp and see when the light comes on. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now