 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / May 2006Request for help with overheating issue on 1990 Mazda MX-6
Hi folks, Appreciate any suggestions the board might have to help keep my 1990 Mazda MX-6 4cy NA on the road. The issue is that in the hot Texas weather, the car will overheat but only in a strange set of circumstances: -- if i drive stop/go around town, under 55mph from the start, the car will run all day without overheating, even at lights, in 100+ weather -- If i drive on the highway, it will go all day without overheating. -- ONLY when i drive on the highway, then exit and return to around town driving, does the car overheat. If i find a road where I can reach higher sustained speeds it will cool back down again. The water pump, timing belt, and radiator are all about 1.5 years old. The car isn't loosing any oil or coolant. I removed the radiator cap and there is no sign of bubbling or oil in the coolant. I have not seen any white smoke at all. To troubleshoot, I've flushed and filled the coolant, replaced the thermostat, replaeced a relay that controls the radiator fan so I know that it works correctly, and replaced both temperature sensors on the thermostat housing (one had broken at the wire connector). The thermostat is in correctly and not reversed. HELP?? I appreciate any further advise!! I'm a poor student and I'm dreading bringing this 16 year old (225,000 mile) car to a mechanic...... THANK YOU > Hi folks, > [quoted text clipped - 10 lines] > town driving, does the car overheat. If i find a road where I can > reach higher sustained speeds it will cool back down again. I believe you have a somewhat marginal airflow through the radiator (or air conditioning condensor and radiator), or perhaps a slightly restricted water flow through the radiator. (1) Restricted Airflow ? Your around town driving indicates that heat generated at low speed is pretty well removed by the fan/radiator etc. Maybe not great, but adequate. At highway speed, the extra heat generated (by the higher rate of fuel consumption) is pretty much removed by the air passing through the heat exchangers (radiator). But, when you slow down suddenly from high speed driving, the extra heat is not dissipated immediately and it shows up as an overheat until the fans, radiator, etc can cool it. Check to see if there is a little trash, grass, bugs, etc in your AC condensor or between the AC condensor and the radiator. Make sure the airflow is not impeded with trash, bent fins, etc. Also check to make sure any shrouding (the manufacture may have used to direct airflow from the fans through the radiator) is in place and functioning. (2) Restricted water flow ? - Sometimes a collapsing radiator hose on the suction side of the cooling system will cause the symptoms you are seeing. A new rigid hose will correct this if it is a factor. -Although you may have flushed your radiator, it is still possible that there is something slightly blocking the water flow. This can be some blocked tubes, mineral scale, whatever. Silicate scale from antifreeze decomposition products has had this effect in some cases. If the radiator is in poor shape, you may have to take it to a radiator shop for cleaning and repair, or may even have to replace it if it is 'rotten'. > > Hi folks, > > [quoted text clipped - 57 lines] > replace it if > it is 'rotten'. HLS offers the most plausible explanations for your symptoms. I would mention one other possibility that I have experienced on your particular model. The ground connection for the cooling fan may develop resistance due to corrosion and as it gets hotter it finally reaches enough resistance to lower the cooling fan circuit current. This causes the fan to run at a much lower speed than it should and does present cooling problems at slow speeds. It is very difficult to visually tell that the fan is running slower, so the best way to diagnose it is to monitor the cooling fan current flow with an ammeter. If the current is less than specs (About 10 amps if I remember correctly) then you need to find the unwanted resistance in the circuit. Another way to check for excessive resistance is to feel the ground wire and it's connections. Any resistance will act as a heater and cause the location to be physically warmer than the rest of the circuit. Sometimes the resistance can get high enough to keep the fan from running at all when it is hot, so you might consider pulling over when the temperature gage is indicating overheating, and take a look at the fan to see if it is indeed running or not. BTW, you did not say if you had a manual or automatic transmission. On the automatic transmission equipped vehicles there are two fan relays to used to make the fan a two speed fan. The slow speed relay is controlled directly by the temperature switch on the front of the engine and uses a dropping resistor in the fan motor circuit to provide slow speed for normal operation. The other relay is used to provide high speed when the A/C is turned on or during overheating conditions. That relay is controlled by the ECM as well as a second temperature switch on the engine. You said you replaced the relay, but did you check both of them? If either low or high speed control circuits are not operating correctly then you might experience the type of symptoms you described.  SignatureKevin Mouton Automotive Technology Instructor "If women don't find you handsome, they should at least find you handy" Red Green Wow, thank you both so much - your help is very much appreciated!! I am going to spend some time working on it tomorrow and tracing down both of your suggestions. I have a few short questions first if I can bother you more... 1. It's a 5 speed car. Are there still two relays/two speeds? Originally, the fan was not coming on at all, and this was fixed by replacing the relay that is under the battery tray. I know the fan is spinning, but I guess I need to check the resistance to as you suggested, Kevin. Do you know where the ground (will cleaning it help?) and the second relay are-- the haynes manual for this car is worthless in this respect as there are so many minor differences between mx-6, 626, manul, auto, na, turbo, etc, i'm sorry to have to ask.... I wonder, I don't use the a/c becuase it needs a charge (leaking dryer), but if iI turn on the system i get a check engine. I need to pull the code tomorrow, but could that be related to an issue with the same relay? 2. Which side of the cooling system is suction? i can feel water flow if i pinch off the top hose into the thermostat, though it's not as much pressure as I expected. Is there a specific hose i can test? Again, thank you so much for your amazing help and time spent. I'll be working on the car tomorrow and will be sure to give you a full report. Wish me luck~! Zac > Wow, thank you both so much - your help is very much appreciated!! > [quoted text clipped - 3 lines] > > 1. It's a 5 speed car. Are there still two relays/two speeds? Not according to the repair manual from Mitchell. The manual transmission equipped vehicles only show one relay and a single speed fan, but I never worked on one with a manual transmission, only the automatic with two relays. It may be that there are two relays and a two speed fan even with a manual transmission, if it also has air conditioning. > Originally, the fan was not coming on at all, and this was fixed by > replacing the relay that is under the battery tray. I know the fan is > spinning, but I guess I need to check the resistance to as you > suggested, Kevin. Do you know where the ground (will cleaning it > help?) There is a connector (front of left front fender). Try following the ground wire from the fan motor. The ground connector is one that can be unplugged and that is where the high resistance would most likely be. It might feel hot to the touch after the fan has run for a while if it has a poor connection. and the second relay are-- the haynes manual for this car is > worthless in this respect as there are so many minor differences > between mx-6, 626, manul, auto, na, turbo, etc, i'm sorry to have to > ask.... I wonder, I don't use the a/c becuase it needs a charge > (leaking dryer), but if iI turn on the system i get a check engine. I > need to pull the code tomorrow, but could that be related to an issue > with the same relay? Possibly, the ECM is involved in turning on the High speed relay when the A/C is turned on. The ECM grounds the relay control circuit in response to a signal from the A/C switch. > 2. Which side of the cooling system is suction? i can feel water flow > if i pinch off the top hose into the thermostat, though it's not as > much pressure as I expected. Is there a specific hose i can test? Lower hose sucks into engine, upper hose flows out to the radiator. Squeaze the upper hose to test for flow and pressure when reving the engine. Observe the lower hose to make sure it is not collapsing. > Again, thank you so much for your amazing help and time spent. I'll be > working on the car tomorrow and will be sure to give you a full report. > Wish me luck~! > > Zac good luck, SignatureKevin Mouton Automotive Technology Instructor "If women don't find you handsome, they should at least find you handy" Red Green Sorry, one more question: Will one of those Quick lube radiator services with the power extraction pump help if the issue is with a slight clog to the radiator? I don't usually trust those places, but if the machine flush will help over my drain/hose flush/fill I'm game... Zac ======= ======= > Hi folks, > [quoted text clipped - 27 lines] > > THANK YOU ======= ======= Not to detract from HLS and Kevin.......... but........ define "overheating". Let's be clear on gurgling noises, hissing, or if you're just going by what you're seeing on the gauge. As to your Q on letting the quicklube flush out your radiator, I would suggest you consinder doing that yourself. You can buy the kit to hook up to your hoses at any parts store. You can use one of the commercially available flushing agents, or do what I do, use Ajax as the abrasive flushing agent. It works. any whooo.... The info on what you're going by to determine that it's overheating would be helpfull. ~:~ Marsh Monster ~sips his mushroom tea~ ~:~ Marsh, Overheating -- temp guage creeps up slowly and there seems to be lots of heat under hood. I haven't let it boil coolant or steam because i've not let it get into the red.....but it would get there easily based on how quickly it rises. I haven't seen the cooland boil in the tank, that would be a sign of head gasket right? Kevin, thanks again for your help. I traced the ground today (it grounds out on the back of the transmission), and cleaned it up really well. I also found that the wire itself was frayed and the connector to the fan was corroded, so I patched all that up as best I could. The electrics under the hood, relays, wires, sensors on this car are a continued handfull -- so I'm hoping your suggestion works!! Tomorrow it's supposed to be 95-98F here, so we'll see how it goes~! I also was told by a friend to try the Mazda oem thermostat, instead of the ones from Autozone. Depending on how the ground wire cleanup works, I'll probably try that next. Thanks guys~~ Willl let you know! Zac ====== ====== > Marsh, > [quoted text clipped - 20 lines] > > Zac ======= ======= Zac, here's what I would suggest based on the facts you've posted so far. First, hotwire the fan so it runs continuously while the engine is running. Then drive this thing for a day and see if the symptom is still there. Secondly, take the t-stat out completely and drive it for a day and see if the symptom is still there. Third, and probably should be first, make sure the radiator cap is holding pressure and isn't weak. The above are simple diagnostic steps you can take to narrow down the area of concern. Lastly, and again based on the facts you've posted, If the above steps don't drop the running temp down to where it needs to be under the circumstances that you've listed, then you should consider having the system checked for exhaust gases using the chemical detector method. let us know, ~:~ Marsh ~:~ |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.