QuestionQUESTION: HI Roland. I saw a couple posts that at first seemed related...but not the same exact symptoms... so here goes. 2002 Intrepid 3.5L, 104k miles. Brand new radiator, water pump (which the previous one also looked new), thermostat, all radiator hoses and belts, fans run well, a/c runs well, it's been bled thoroughly, no air coming out of bleeder valve. We're about out of options, thinking maybe fan relays?? So here is the story. Hot temperatures outside (Texas 100 deg), a/c running full blast and cold, car runs at normal temperatures. Cooler temperatures outside (whether winter or summer 80 deg), whether with a/c running or without, it will run normal anywhere from 15-30 minutes, temperature quickly starts creeping up, if you're in drive, drop it to 3rd where the RPM's go up, and the temp starts falling (or rev it, and it drops down). More apparent around town, but it does creep a bit in highway speeds. Apparently there are two fan relays, one low and one high. We're thinking that one may be bad, since when the temps are really hot and the a/c has to work hard, the high relay works well. When there isn't much load on it, the low may be struggling. We would love to hear your thoughts on this... The car never technically overheats if you keep an eye on it, but this is for a teenager and I don't want her driving it like this. My husband used to be a mechanic and I'm pretty car savvy myself. If not the relays, what else would you try? If we replace the relays and still same issue, any other suggestions? Thanks for any input you can provide.
ANSWER: Hi Ana,
There may be a misunderstanding of what you believe is normal temperatures and what the Chrysler engineers consider normal temperatures, and how you define 'overheat'. Typically needle readings any where from 1/4 to 3/4 of full scale is considered a normal operating range. In the absence of readings consistently about 3/4 scale the system is operating safely. The accuracy of the gauge is another possible factor to consider. So if you find that you are running consistently above 3/4 scale then it would be appropriate to measure the actual temperature of the coolant via an infra-red gauge and compare that to the boiling point of the coolant (which depends upon the ratio of anti-freeze to water in the system). That would give you an idea of how close you are running to the point where you would have boil over and loss of coolant.
As to evaluating the functioning of the fan relays you would want to stop from time to time and evaluate the fans' speeds in comparison to the needle reading, and ideally with some knowledge of the actual temperature associated with a particular needle position. The control of the fans is based upon about 5 factors (coolant temp, ambient temp,speed, ac in use, transmission coolant temp) and it is slightly different depending upon which engine you have in the vehicle. As I read the manual, if fans are called for both fans should always be operating, but either at low or high speed. So you could observe at least that both fans are operating.
I have the '98 and '04 Chrysler service manuals that spell out the programing of the fan control system as a function of temperature of the system, ambient temperature, a/c operation, etc. They differ from one another, so to determine which you have in your '02 you could take a look in the power distribution box under the hood and notice whether fuse B (next to the in-board-most fuse in the back row) was 30 amp or 40 amp in size. Another clue would be whether there were secondary relays, one for each fan, mounted close to each fan on the module proper or not.
Once that is determined I can xerox copy and postal mail you the protocol for fan operation which can be related to the various operating conditions but to make use of it you would want to have some basis for relating the needle positions to actual coolant temperature via the reader that I mentioned earlier.
At that point you can draw conclusions about whether you need to do anything or not. Absent any real sign of overheating, that is a conservative approach to evaluating your situation. It may very well be that there is no issue and that nothing needs to be done.
Roland
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QUESTION: HI Roland...
So a follow up. We replaced the fan relays on the PDC, but it still didn't fix the issue. We also replaced the fan assembly because we had a bent shaft that started to make noise. We sent it to a dealer and it's been there for the last week, but all they have been trying to do is throw new parts at it and not actually diagnose anything. I don't even think they have put it on the computer. Needless to say, we told them forget it and we're just going to get the car back. I downloaded the service manual last night and noticed the 3.5L does show 2 fan relays on the fan assembly, though we didn't notice them when we replaced the fan assembly. We have since also gotten a code reader, as the engine soon light was dinging though we can't see it on the dash. Either way, it's tripping a cylinder misfire code. After doing a bit more research last night, we found someone had the a cylinder misfire code and they replaced the PCM and it fixed it. I guess the question here is.. Could the PCM cause both the cooling issue and the cylinder misfire? The dealer was able to tell us that they were able to see that the fan were slowing down (assuming the PCM is sending that signal to the fan relays)... I thought I would see what you thought about my theory... could a bad PCM be causing both issues? Thanks in advance for all your help!
Ana Weaver
ANSWER: Hi Ana,
It is possible that the pcm is the issue, but for either issue I would do a lot of diagnostics before going that route. There are about a dozen reasons other that the pcm for a multiple cylinder misfire that I would want to look into (at least the more likely ones) and similarly as I suggested to you earlier I would want to follow the behavior of the fans with regard to the protocol for their coming on/off as a function of temperature (as described in section 7 of the manual) and verify whether or not they are behaving as designed before changing the pcm. Again, how about the question of the accuracy of the gauge? Absent actual coolant discharging I would be reluctant to accept the diagnosis that it is truly overheating.
Roland
PS: Here is a recent reply I sent to another owner with an 0300 code:
The manual gives the following possibilities, in addition to the wires which were replaced:
fuel pump or filter (unlikely as regards the filter), injector harness connectors, ignition coil circuit, spark plug, mechanical problem (but compression test would probably have shown that), contaminated fuel, water in fuel. pcm power ground connections, injectors, restricted exhaust, intake restriction, the pcm itself, the evap emission control system, the exhaust gas recirc valve system (this is something I would certainly recommend that he check, as if the valve sticks ajar it will definitely cause misfiring. So suggest that he lube the valve stem with WD-40 and move it back and forth with the tip of a screwdriver in the slot to be sure it is moving to a dead-stop via internal spring-action), air gap at high rpm's, other mechanical (?), and damaged trigger wheel (something to do with one of the engine postion sensor (?)). The parenthetical items are my remarks.
Many of these also might set a separate code so he might not need to concern himself with them. But the egr valve would be high on my list.
Let me know how this progresses, please.
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---------- FOLLOW-UP ----------
QUESTION: HI Roland.
More detail..the coolant does discharge, so we know it is trully overheating. We are still running diagnostics on both issues, but I needed clarification. The service manual states that the 3.5L should have two additional fan relays located between the fans in addition to the ones we've replaced on the PDC, however both the fan assembly that we pulled off the car that was working before and the new OEM replacement don't have that. It looks like all OEM parts only list one part number as a replacement for the fan assembly, regardless of whether it's a 2.7L or 3.5L, and it doesn't have the two additional fan relays. The car was manufactured in 05/2002. I'll be calling a dealer to see what they can find as well...A bit more insight on our history of the car. We bought this car used in Oct/Nov 2009 for our daughter. It did not overheat when we bought it, however, once temps got a bit colder here in Texas, we noticed the heat wasn't working, so we decided to look at the thermostat. It didn't have one at all, so then we put a new thermostat, and that's when this debacle all started. The thermostat opens up and we tested the flow (working with accurate temps).
Thanks for all your help!
AnswerHi Ana,
I don't have an '02 manual, but rather the '04 which does show the additional relays at the fan module for the 3.5L (but not the 2.7L).
If the '02 manual shows them, that is the same. Again, what are the fans doing as a function of the coolant temperature is the 'bottom line'. If the fans are coming on when the temp is rising, then that is all you need. So here is another possibility:
Because it ran well, although cold, when you got it, and the problems then began in the summer after a thermostat was put in, may I suggest that you consider the temperature 'set' of the thermostat that was installed? Thermostats can be purchased with a 'set' of around 180F or of around 195F and so you may just have a thermostat with two high of a setting for the fans that you have there.
Is there any chance that the original fan/housing/relay is available from the place that took it off? I am not clear why the double relays are needed (unless it has to do with gauge requirements for the wiring; it takes thinner wires to control a secondary relay then to send the current all the way from the PDC to the fan motors) but it would be better to have the original wiring set-up if you can re-create it economically.
Roland
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