95 GT Running very hot

Discussion in '1994 - 1995 Specific Tech' started by JesusOnIceSkate, Nov 12, 2007.

  1. Gentlemen please help!

    I've posted about this problem on other forums and received great help..almost narrowed down the cause:

    My stock 95 GT is running very hot: Radiator and thermostat are new. No problems with heater core, or water pump...hardware is OK and coolant is circulating as it should. The problem was narrowed down to the cooling fan not turning on:

    Cooling fan runs on low speed when temp is very high (208F+).
    Cooling fan DOES NOT run when Max A/C is turned on...as it should.

    Further diag of CCRM revealed that EDF and HEDF relays appear to be fine since when ground / voltage are applied to control side of both relays the fan DOES RUN at right speeds as was done in this test:


    When ground is applied to pin 17 (Light Green) high speed fan truns on OK...to me this indicated that High-Speed HEDF relay is fine

    When car is very hot (past L of NORMAL) pin 14 (Dark Blue) has current and low speed fan runs OK..to me this indicated that Low Speed EDF relay is fine.

    So...since the relays are ok...are these assumptions correct:

    1. In the above circuit Powertrain Control Module (PCM) decision-making-steps are not grounding 14 (Dark BLue) when Max A/C is truned on (because fan should run at high speed

    when Max A/C is on...which it does not)

    2. Powertrain Control Module (PCM) is supplying 12V only when car is very hot to turn low speed fan (this may be by design per earlier post---low speed fan turn on 208*F+ )

    3. If Powertrain Control Module (PCM) thinks that for whatever reason the fan should not be on.....is it correct for me to assume that a sensor of some sort or other is

    feeding PCM wrong info thats involved info PCM's decision making process as to wether or not to turn the fan on? .. in which case I can troubleshoot the sensors involved.

    4. Is it possible that it's the A/C High pressure Cutout / Fan swithc in the above diagram?

    Any pointers would me much appreciated....this puzzle is almost solved

    Attached Files:

  2. My fan comes on with any of the A/C settings... normal, Hi, Bi-level and defrost.

    If that's any help...
  3. Thanks! I was told that turning Max A/C on with engine of and key in running position forces high speed fan to run...it's a way to diagnose oddities in CCRM etc.
  4. As noted, you should have low coming on at 208*F. High comes on with Max AC or at ~226*F.

    So you NEVER see high speed coming on?

    If your LS fan comes on at 208*F naturally, one might infer the ECT is calibrated. The ECT tells the puter what your engine temps are.

    I'd be thinking more that your HEDF driver in the PCM took a dump. This would keep CCRM Pin 17 from ever having continuity to ground naturally (you saw it works fine when you manually ground it).

    The AC works normally, correct? I ask to rule out an issue with the WOT relay.

    If needed, there are a couple of ways to rewire the circuit. It doesnt sound like you're interested in doing this but it is an option. I lost the HEDF driver and went to an aftermarket controller after some rather exhaustive testing.

    You've probably seen it but here are a couple of tech notes about the cooling system and CCRM. You have to pick and choose what applies to you.

    Tech note 1

    Tech note 2.

    Good luck.
  5. Pull up the codes, temp sensor may be bad? :shrug:

    My gf's 95 GT had the same problem and it was the sensor.
  6. Theres a write up on sn95forums.com about how to get manual control of your fan in case its something you cant fix right away.
  7. The SN95 forum write-up has some inaccurate parts.
  8. Yeah it's supposed to be 226*F but my high speed fan doesn't come on until the gauge needle is at the end of the NORMAL zone and almost creeping into the red. That's way too late for the high speed fan to be much use.
  9. No fault codes but test does run fan at both speeds

    Thank you all for help...I really appreaciate this. HISSIN50...thank you for the details:

    You are right AC Works normally...no problems at all.

    I never see HIGH speed come on possibly b/c when temp reaches 208-ish..low speed kicks in for about 30 seconds and knocks temp down slightly...so temp never really reaches 226*F...I'm positive that it doesn't go on after temp needle is past last white line towards red, which I'm assuming is approx temp of 226*F+, and it certainly doesnt kick in with car hot and Max AC on and key in run / engine off.

    BUT :bang:...not sure if this helps: When I ran the codes last night (everything clean..no faults reported) the KOEO test DID TURN ON THE FAN AT BOTH SPEEDS .. high and low as part of the test. Does this in any way help pinpoint or exclude HEDF driver in the PCM?

    Also, is there a way to test Temp sensor / sender units .. or is this something that would show up on the ODB1 scanner duriang diag?
  10. In my case, the puter was also able to cycle both speeds during codes. It just never ran high speed with the AC on (on mine, when the AC was on, low speed stayed engaged instead of switching to high speed).

    WIth the ECT testing, it can be out of calibration but not out of absolute spec (hence no code). That's why I surmised that if the low speed comes on right at 208*F, then the ECT is probably calibrated (it would be weird to be calibrated at 210* but not at 225*).

    For ECT checking, look for ~0.50 volts at 210*F and 0.36 volts at 230*F.

    If you pull the sensor and put it in water:
    215*F = ~2.05K Ohms.
    230* = ~1.55K Ohms.

    You might notice the voltage and resistance readings are of the same trend (going up and down together). There's a thermistor in the ECT.

    Good luck.
  11. Nooooo!!!!! it's not just electic anymore...

    I disconnected the ECT connector and checked resistance on the ECT after running the car for about a minute or two (luke-warm) and very hot as indicated in this test:


    The ohm meter (when set to 20K) read 13.85 at lukewarm
    It then read 2.66 at overheating temperature.

    Since resistance drops with temperature increase...and (per article at about.com) should be between 700 and 1000 at normal operating temp....does resistance of 2.66 (which scaled I assume means 2660) means that the ECT is telling the PCM that car is cooler than it actually is?

    Also, the ECT was changed by dealer not too long ago to fix fan not-turning-on problem did they put in a wrong one or :bang: ?? Here are photos:


    I tried running the car with ECT disconnected...I get check engine light but the fan does run on high speed the moment you start the car...I guess this is a fail-safe.

    I am afraid that there are bigger problems here however. Last week I took the car out on the freeways....it ran hot on streets at about 20-30 mph average as I was expecting, but on the freeway it cooled down to MA of NORMAL.

    Last night I decided to take it for a drive (I love this car since my daily driver is a sluggish SUV) on freeways expecting it to run cool....no luck it's overheating on freeways now as well :shrug:! This is with new radiator and thermostat. When I came back the temp needle was in red...and the fan was blowing...but apparently not helping much. I checked upper hose to see if there was any appreciable pressure...it was hot but pressure-wise not much different from when engine is cold..does this mean anything? I know this is a loaded post and I appreciate you guys reading this. I guess my questions are:

    1. Does high-temp (Temp gauge reading past L of normal) resistance of 2660 (normal is 700-1000) indicate that sensor is bad?

    2. Am I looking at a bad waterpump? I'm assuming that at freeway speeds, fan or no-fan the circulation should be adequate to cool the car. Since there is no pressure at upper rad-hose (as there was b4 I changed radiator) I'm assuming water is not circulating due to bad pump.

    3. I plan to remove remove thermostat and disconnect the ECT and take the car on freeways again this weekend (this insures that fan is blowing and new 180* balanced mr.gasket thermostat is not restricting flow). If the car is overheating am I correct to assume the waterpump is a gonner?

    4. When the needle on temp gauge is on MA of normal...what temp is this approximately? And when it's border-line red what is the temp then?

    Thank you again for all your help
  12. As far as the factory gauge is concerned you have to take the readings with a grain of salt. They are notorious for being inaccurate.

    I've been having the exact same issue for over a year now. Just like you describe, low speed cuts on fine at 208* but the high speed would never come on (AC or no). I ended up disconnecting the CCRM from the fan completely and hardwiring a manual switch to the high side of the fan. I would have liked to keep everything factory but the programmed temp settings are way too high.

    I looked into some of the stuff at delta control but it seemed their models only had a single output, and our fans have separate inputs for the two speeds. I've been toying with trying a little more elaborate relay setup to control the fan but it has been a long time since I worked with this stuff so it might be way off. Finding a solid 2 speed controller would probably be the best route, but I think these would work for those that don't want to mess with temp sensors.

    On a side note...Hissin which controller did you end up going with?

    This setup turns the low speed on with the ignition. When you activate the manual switch it kills the low speed relay and activates the high speed.
    View attachment 347863

    Here is the same setup with an added 1/2 sec delay on the high speed.
    View attachment 347865
  13. I think your resistances are ok (where they should be).

    ECT Disco'd indeed failsafe's the fan being on. THe default is for the fan to be on and the PCM shuts it off. Part of this is due to the EDF controller (which I've never found any great info about, in terms of internal workings BTW).

    Ensure the system holds pressure. And if you have doubts about the cap (and it has some time on it), replace it. Each PSI in the system raises the effective boiling point about 2.6*F. 16 PSI = ~45* increase in the boiling point.

    I really doubt the water pump took a dump. I'd get the fan going on high (one way or another) and then see what it does. If it can cool fine at low speeds and while stationary (but still runs hot at speed), I'd be looking at something else (non pump) as the cause (since you can cool ok while slowed).

    94' Five.0, I went with the Delta Controller. It takes our fan from being two speeds to infinite speeds (it uses PWM). I LOVE the unit (that's why I included it in the cooling system synopsis in my first post).

    You drew up some nice schematics. I like the RC portion.
    Another option for your relay-driven controller would be to use a thermo-switch (for low speed) and a third relay to shut off low as high engages. This might get you some extra run-time out of your fan (so it's not running when the t-stat is closed).
  14. Nice suggestion with the thermo switch, I'll have to play around with that. Which delta piece are you using? FK-35? Sorry I'm not following PWM.

    Sorry, I'm not trying to hijack this thread.
  15. Yep, the FK-35. I used it with the stock fan and now use it with a Taurus fan.

    PWM: Pulse Width modulation (like how our IAC's work). The Delta unit has a target-temp which you choose (mine's 188*F, centered around a balanced 180*F t-stat for instance). The controller spools the fan as much or little as needed to maintain the target temp.
    The controller soft-starts (removing the big shock on the electrical system) and with its variable nature, unless it's hot (over 95*) out, the fan seems to run at 25-75% of its capability to maintain temps.
  16. Wow, I wasn't aware thats how it worked. That is very very cool. So the single leads coming from the FK-35 connect to only the high side of the fan? After browsing through the install notes I noticed the temp sensor just slides in between the radiator fins. How difficult was the overall install? Any modifications or extra accessories from their site required?
  17. You got it. You connect it to the high-speed terminal so the fan is capable of running at 100% of it's ability. You could connect it to low speed but 100% of low speed is the highest the fan would run.

    The probe Brian uses is very nice IMHO. I have an alum radiator and had no problems installing the thing. It's kinda neat - when the probe heats up, the resin in it gets gooey and conforms to the surrounds, helping it to have a good contact interface with the fins.

    There's a lot of engineering in the controller. A neat side effect is that since the probe goes on the radiator outlet, when you're cruising down the highway, the fan can actually shut off on it's own. With probes that mount at the radiator inlet (as most others on the market), that can almost never happen.

    Note that if you have dual fans, talk to Brian (or I can try to help). Some need a filter (which he sells for cheap) because the controller sees a huge start-up draw in a fan motor (or the inconsistant start-up draw in dual motors) as a short and the controller shuts off to save itself. Neat feature. You also use a filter if you have a battery far from the controller (in the trunk, etc).

    The install is easier than any other fan controller I've ever seen. Brian supplies all the wiring and connectors - you really need to add nothing (sans wire loom or custom stuff like that). You connect the power and ground wires to the controller, run a power wire to the high-speed fan terminal (from the controller), ground the fan's neg terminal and that's really all you *need*. You also hook up an ignition lead if you want the fan to shut off with the key (or you can have it continue to cool the car after you shut it off. If so, the ignition wire is connected to constant power. Your choice). And there's an input for AC. The fan defaults to running at about 50% at all times with the AC on, and then as you hit the target temp, it ramps up accordingly.

    If you have underdrives, Brian has a jumper to run the fan at 10% at all times to help accomodate the loss of efficiency with the UD's.

    And you can always change your target temp by changing the jumpers (there are many preset target temps you can choose).

    Things I think are must have's: get the rheostat. It replaces the above-mentioned target-temp jumper. You now have a knob in your cockpit that allows you to raise or lower your target temp. I really like this. In the winter I run my target up to around 195*. And when it's 115* outside, I keep it at 185-188* because I need to get things cooling as fast as possible (but while still avoiding hysteresis with regard to the t-stat). That's what's neat about having PWM and a target temp - you dont need to have the lag of the fan coming on at 195, off at 187 (as an example). The controller just does what it can to keep you at your target (plus or minus 3*F as I recall).

    And get the LED. It changes colors as the fan ramps up, so you have a good idea of how hard the fan is running (a rough idea of the duty cycle of the controller). I really like that, especially since the fan runs so quiet at times that I have a hard time hearing it (and would wonder if it was on).

    Anyhow, that's what I can think of. I've had nothing but great customer service from Brian - he did very well by me (and continues to do well by me. I have bugged him a time or two after the install. He even took the time to make me a custom schematic for something I was working on). :nice:

    His ordering procedure has changed recently but you can still backdoor his site and look at his products and read his tech links too.

    I'm happy to answer anything I can.
  18. Still need help ... ran the temp stats...

    Hey guys...I had the cooling system flushed and oil changed yesterday..was hoping this would help slightly but no luck. I picked up an infrared temperature scanner to see if I can get more accurate readings than the stock temperature gauge... these are the results. It looks like the fans are coming on as they should after the flush, but the GT still runs super hot (according to temp gauge in the car) even with fan set on high. I think 180* Mr.Gasket may be restricting flow too much. I also tried 2 different radiator caps...didnt help, also with fan-always-on-high didn't help


    Do these temperature seem reasonable? I was pulling over and taking readings..so there's minor latency, but the trend is pretty obvious. I'm going to take out Mr.Gasket tonight and map the results as I did above to see if there is an improvement :Track:
  19. Wow, you must be an engineer. :rlaugh: Cool chart. :nice:

    As far as interpolating your fan (only) data, it seems fairly ok, does it not? You have that anomaly where while idling, you lost the low speed (at 205 ECT*)

    In the driving portion, it seems ok (though there was quite a spread from where high was not on until it was on). When it's real hot out and the AC is on, I would continue to heat up with only low speed working. That's not an issue for you though.

    One aside: I've done similar testing of in and out radiator temps and you have a ton of heat-rejection occurring. There are myriad variables (to which it can likely be chalked up to) but seeing your numbers was interesting.

    I really like your idea to remove/swap the t-stat. I dont like how little heat rejection you had (until 200-214*F).

    Given how hot it's running, I'd still want to pressure test the system if you have doubts. You've seen that even the fan on full bore doesnt help.

    Two thoughts on the gauge movement with electrical loads:
    1. A bad ground can cause gauge movement with respect to loads.
    2. In theory, the diversion of current to the new load could slow down the fan, but if the gauge moves even when the engine is cold (t-stat is closed, fan is not needed or doing anything even if it's on), then I'd still think gauge and gauge grounding.

    I would really recommend grabbing an aftemarket mech gauge. Even a parts store version (they work fine IMHO) for 15 bucks will really help narrow this down. All the IR stuff is cool but since there is an apparent issue, simply having a real gauge till this is sorted out would be something I'd want. Not to mention that I've had variances in the IR readings for no known reason (that I could decipher).

    You can hide the gauge under the dash or in the glovebox if you wanna' keep it out of sight.

    This really is interesting.
    Good luck.
  20. I really appreciate all the info Hissin. It's time to throw out all my random relay sketches and pick up the delta unit. It sounds like the perfect solution to what has been a very frustrating fan issue.