Thank you for your help here: '97 and has been sitting for about 10 months. Never a problem with the fans. Started the car to warm up and to check the oil. Within a few minutes the engine overheated and overflow of about a gallon of coolant by the time I collected myself and moved the car out of the shop. Up to this point, fans would always cycle, but I was not paying attention at the time of this issue. What has been done thus far: Check all connections (the ones I could see) and made sure there was no corrosion. Everything looked great. ID the fuses for both fans #6 @30a, #8 @25a. Both good but replaced them anyway.... ID the fan relays (H) for water, (I) for oil. Both relays are identical and tested across the coil @ pin #s 85 & 86 with readings of ~73 Ohms. Think these are considered good as test range suggests 50-120 Ohms. Refilled the colling system with more AF & distilled H2O to about 3/4" from top of reservoir. Added a couple of Qts oil. Restart and engine runs fine, heats up what is thought to be a bit fast, fans kick on @~190F run for maybe 10-15 seconds and lower indicated temp a little, shut off and do not restart with water temp rising well past where start point should be for the fans. ID the temperature sender for water, but not tested. ID (what I'm calling the power sending regulator) for the fans located at bottom of radiator where 4 wires enter this unit and seem to feed each fan. Oil temp sender has not been identified. Pictures for reference: Image Unavailable, Please Login The "so called" power regulator for fans: Image Unavailable, Please Login Water temperature sender: Image Unavailable, Please Login Will greatly appreciate help diagnosing and obtaining the parts needed to remedy this situation. Thank you.
Is it possible that your thermostat is not opening all the way up and not letting enough hot engine coolant reach the radiators (and the temperature switch on the radiator)? Unfortunately, no one on FChat seems to have access to 456GT/GTA wiring diagram, and the WSM doesn't go into enough detail to enable a proper diagnosis of the electrics involved in heat management. As you have a 97 model (with a 5.2 engine management system), however, it may be close enough to the 456M (5.2) to draw a comparison. I'm not sure if the M car has power regulators... and I can't explain why they have 4 wires. Experts??? To eliminate one confusion factor, was the A/C turned off during your tests? On the 456M, an AC pressure switch is activated if the demand is high, turning on the RH fan. The HVAC ECU is also sent a temperature signal from one of the engine ECUs (which have a coolant temperature sensor input). This may be another way that the A/C turns on the RH fan. By the way, when you had your overheat/overflow incident, was the AC running?
Thanks for your post, Ian. Pretty sure AC was off. In reference to the T-Stat, when restart, felt both large lines from engine to rad for heat. Right line would heat first then the left (with T-Stat housing) would heat up followed by subsequent cooling. From that, concluded the T-Stat is working...... Further, looked in reservoir to see if coolant was moving and it appeared to have motion. Will start the car tomorrow and turn on AC to see if the RH fan fires. Thank you for your time and help. Greatly appreciated!
The gas pressure switch associated with the RH fan is activated at 15 bar, so it will take a large demand on the AC to trigger the fan. You may have to heatsoak the cabin, then turn up the A/C to max cool. Bear in mind, of course, the potential to overheat the cooling system. I'm not sure what logic is required for the HVAC ECU to turn on the fan. I might have to re-read the WSM again.
I don’t believe there is a ‘power regulator’ for the fans, that's the accelerometer and unrelated to fan operation. Besides pulling the fuses and relays, did you remove the blue and yellow plug on your fuse board and check for burned plastic and pins? other than refilling the system did you also bleed it? If it boiled over like you said there is also likely air in the system now. As well as the condition or replacement of your coolant cap to allow it to pressurize. Post or search over on the 456/550/575 forum, we have lots of good info on the cooling systems of our cars, maintaining, upgrading and thoughts on the (alleged) shortcomings of the design.
Since the last time, here is what was done: Attempt to make sure the cooling system was blead by raising the nose of the car (top of radiator) to a bit higher than the Surge Tank by the battery. Turned on the AC and the cooling fans came on almost instantly and cycled keeping the engine at or just above 190+F. Ran the car for 30 minutes in this configuration. Noticed a little drop in volume in surg tank when the 30 minutes elapsed. Played with the HVAC controls: The STOP button did just that.... stopped the cooling fans. Stopped any cooling/heat entering the cabin. Turn OFF the STOP button and engine cooling fans resumed running and cool/heat for the cabin also resumed. Thought this was a bit weird: When the cabin fan was turned off, independent of the STOP button, the engine cooling fans would ALSO TURN OFF. With the cabin fan turned on, and any temp. selected, the engine cooling fans worked just fine..... So, is something screwed up? Have to have the HVAC ON to keep the engine from overheating while parked? Very interesting. At least, the car can be driven as long as the HVAC fan is selected to ON. Thoughts/diagnosis or any WAGs would be appreciated. My Best, DJ. BTW, that larger relay/module/switch (whatever) looks like it runs directly to the oil cool fan. Picture #2 above.
Not sure what triggered the RH fan stop. It could have been an electrical signal directly from the HVAC control panel/ECU or the loss of gas pressure (with the AC compressor turned off). With the loss of gas pressure, the 15 bar switch (on the receiver/dryer) is opened and the RH fan relay coil loses its earth (ground). Again, the 15 bar switch should only be active with relatively high demand for cooling. I assume the AC compressor turns off when you turn off the blower fan. What's the point of having the AC compressor running if there is no airflow into the cabin? Can you or someone else confirm (or refute) this? This may help us understand the logic a little more.
The sensor in the lower right corner of the radiator is what should turn on the Right side fan when water temp rises above 197* That should happen independently of the A/C running or stop switch selected. Part number 158655. Easy to access and remove, but will need to drain and refill/bleed coolant. I suppose you could trouble shoot by connecting a new sensor and inserting into hot water and see if fan turns on with only the key on. The sensor under the manifold has integrated function with both water temperature and HVAC and ECU function. Part 125769 You should have fan operation of the right (and left) without needing to run the HVAC system. I would still inspect the connecting the plugs in the fuse box for burned connections. Since you have a 97 with 5.2 Motronic, you should have an OBD2 port and can pull coolant temp. That may alert you to any faulty readings for the one under the manifold. See this thread for what sounds like a similar issue another user was having. https://www.ferrarichat.com/forum/threads/coolant-temperature-and-intake-air-temperature.696740/
I could be wrong but I do not think that the input from the coolant temp sensor dedicated to HVAC operation can be retrieved with an OBD scanner which connects to either ECUs only, thus will only get information from engine-related sensors.
Just be aware that on some V12's, you may have to have the engine running to get a reading on both banks for the temperature sensor Image Unavailable, Please Login
Thank you again for your time and help. Have tested the cooling system again with the HVAC system not engaged. Fans worked well for several cycles but then, they did not reengage well past 197 F. At this point turned on the cabin fan and the engine cooling fans came on soon after. Tried to determine if AC Pump continued to run on subsequent engine run and noted when the temp switch was moved from cool, and with engine cooling fans not running, believe the relay for the AC pump engaged with the classic thump. Assuming the AC Pump did shut off with the command for high heat. Removed the AC Pump relay and tested across #85 & 86 and ohms were ~78. Concluded the relay is good. As per your request, removed all of the wire connection plugs and inspected for overheat damage. All pins showed no sign of overheat nor did the pin blocks show any signs of deformation due to heat and there were no signs of corrosion. Greatly appreciate your help and links to other information. DJ
Sorry, missed your message. It looks like you are correct. I could find no wiring from the ECU to the HVAC ECU even on the 456M. The engine sensor is only used on the 550 ... and the ECUs have no access to the data from that sensor. I see the 456 (HVAC) radiator fan control test is done with the engine at 2000rpm. Perhaps that makes a difference to compressor output. Running the tests at idle may not provide the consistency required. Image Unavailable, Please Login We really need a diagram for fan control on the 456 (5.2). On the 456M, the HVAC ECU receives inputs from: Sun radiation sensor Outside air temperature on the driver's mirror Sensors in the cabin and aircon ducting Since the HVAC ECU can turn on the RH fan, it may be working with some or all of these sensors to control the RH (radiator) fan (and A/C compressor, blower fan, etc). This I really don't understand. Why is it working sometimes, then not. Also, with the HVAC system not engaged, why should there be any change to coolant temperature or gas pressure. Does cabin heating work on the 456 with the AC OFF (blower fan on)? On some Ferraris, turning off the AC closes the hot water valve. Don't rely on the WSM or owner's manual. These have been known to be wrong about this.
The only way the big fan gets powered is still thru relay H. Despite the different issues turning on it all runs thru that and out to the fan Either your thermostat isn't opening and the temp reading for the fans is low or the temp sensor is your radiator is suspect. Do you at least have a heat gun Per your second post, there may still be coolant circulating when looking into the reservoir. Did you bleed the coolant thru the bleeder screw on the T-stat housing or only raise the front end? The indicated temperature is from the third sensor under the manifold.
Thank you for your post. Only raised the front end of car. I'll look for instructions on using the bleed screw/nut @ T-Stat housing. Thanks again for your help. DJ
We know the thermostat and the pump are working, but are they working well enough. On the subject of air in coolant systems in general, how is circulation suddenly stopped by trapped air? There was hot water circulating before. What, precisely, changed? Did the hot air take up more volume in the system, leading to loss of pump action? We know that liquids are hard to compress, so is the conversion of coolant to another form (steam) creating less fluid and more “gas”? Is less water (and heat) getting to the thermostat and it is reclosing? Are the radiators actually getting colder, so no fan action? Is this why the 550 HVAC ECU gets coolant temperature, so it can control the radiator fan. Note also that the 550 also has emergency/backup control of both fans using the sensor on the manifold. Good point. Perhaps cars should have two temp gauges. One for the manifolds and one for the radiators. We don’t know if the temperature at the radiators is rising as fast as the heads.
“Played with the HVAC controls: The STOP button did just that.... stopped the cooling fans. Stopped any cooling/heat entering the cabin. Turn OFF the STOP button and engine cooling fansresumed running and cool/heat for the cabin also resumed.” Seems to me your ac pressure switch is working great, but your radiator temp switch is failing. Both start the large fan. Replace radiator temp switch. Fairly cheap and likely a common part so check the cross reference thread. My guess is that fixes your large fan problem. I am not certain you have a small fan problem. Consider doing the fan relay retrofit. This is an easy hack and you can get a kit from Ricambi or make your own. I made my own and run a second 10 second delay relay for the small fan that triggers off the large fan. I don’t worry about my fans coming on or overheating the relay board.
The radiator fan switch closes around 190 to 200 and the manifold warning light turns on around 215-220. Assuming those are working properly we do have some feedback.
I agree, I don't think the problem is that deep. Change the fan temp switch, possibly swap out the Tstat, bleed properly and consider getting a new radiator cap. I'm the one making these. I'm still a bit modest about pushing then myself, but once you do sort out the actual problem, it would be a good idea to add one. But my fan kit won't fix other problems that exist. A bad temp sensors or air in the system is still an upstream problem from the fan bypass advantages. It's hotter than that. Even the manual says up to 239* is considered within range. Idling along on hot weather you can easily see 220, but it does seem to plateau there on my car. I think another perception issue on the original GT cars, is the gauges aren't angled toward the driver, so temps actually look hotter than they are until you look them perpendicular.
From the 456 manual for filling... It's assumed you know where and how to open a bleeder screw. It is on top of the T-stat housing.
IIRC specs I found for the warning light was 215 +\- 5. It’s an odd French unit and not Bosch on the 1995 456 GT. NLA too. Perhaps the later years have a higher threshold. Maybe that is how Ferrari solved this problem
Thank you. finally found these instructions in the owner's manual. Actually, think I'm good on this now. Can get the cooling fans to work and keep the engine at normal operating temps while driving and at idle as long as the cabin fan is turned on. Going to send the car to an independent for service over the winter months and he will get my 355 first for belts this October. Will get back to everyone here on what is found and for now. leaning towards the sender in the lower right of radiator as the culprit. Again, my thanks to everyone that gave up their time and knowledge to help me out. My best, DJ Image Unavailable, Please Login
It’s not the cabin fan that is keeping your radiator fans on. It’s the AC pressure switch. Keep the AC on while you are driving it there. Turning the temp up while in auto mode may cause the ac to turn off and thus shut your fans off.
Yesterday, drove the car for an hour and at various speeds... Interior temp set to higher temps but not max. Cabin fan set at #3. Engine cooling fans ran at this setting and water/oil temps were normal. To have pressure at the AC switch, is the AC Compressor engaged? Hope to have as much information on this issue so that when the car is turned over to the independent, he won't have to chase the issue as much. Again, my thanks to you Sir!
Yes, but as said earlier, it’s a 15 bar switch. The demand for cooling has to be relatively high. In Auto, the compressor may turn off when the cabin temperature reaches the set target temperature and the gas pressure switch will be deactivated.
