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You need to get that rear seal resolved no matter what- yours is well and truly buggered just like mine was some 22 years ago. The steel is pretty thin walled and they cave in relatively easy- I thikn I used one of my wood chisels to pursuade it to give way.
The internal recirculation circuit has less resistance to flow than the radiator circuit that has the additional incumbrance of having to flow through the hoses and the radiator- and heat exchangers need a credible pressure drop across them in order to work efficiently.
Although a dodgy impeller cannot be entirely ruled out my experience with such failures [happened twice] is that once those things go south there is no mistaking it and there is no way back unless it is slipping rather than detachment like I saw. Running the engine in such condition is asking for a seizure and once that needle goes into the read one shuts the motor down without exception until one fathoms out what is going on or it has cooled down.
The fans are controlled by PWM [pulse width modulation]. This is a soid state control unit that instead of using a resistance to control fan speed switches the power on and off rapidly to simulate the effect of a lower voltage and thus is more efficient. These units are very reliable but nowadays they are falling over. These units can be rebuilt albeit I am not sure if that is what Roger does. Sounds as though there is a good chance the unit is failing given the erratic running. The alternator generally provides a good power feed above about 2500 rpms and you should see 13.5 volts even with the fans running. At idle the voltage will drop some
You also need to check that the slats in the nose are opening and staying open. Best thing to do with that system is to isolate it and wire the things open . Better still in a warm climate is to remove the slats altogether as that improves cooling air flow a bit.
What happens with the engine shutdown is largely irrelevant. For starters anything electrical running is at battery voltage which should be 12.5 volts and less if a heavy load such as the fans [about 40 amps] are running.
IMHO.. just wait until the flaps open then unplug the Slat Motor, that will keep them open. however I've found if working properly no mods or changes are really necessary under normal conditions here in the US.
EDIT: I see that Stan earlier recommended pulling the Flap Fuse, I'd go that route as it will keep the connector contacts cleaner
I confirmed the slats are open and I pulled fuse. Going after the water bridge as soon as the gaskets arrive as I cannot get that back gasket area clean with it mounted on the block. BTW: This is the thermostat that was in the car. I’m not getting a warm and fuzzy about the last owner so could you guys confirm this thermostat was place in the car properly?
thats installed correctly,
I would suggest to use DC111 on the T stat O ring.
Please consider this next statement.
I would remove the top rad hose for more access,
I would not remove the water bridge,
as you might also have to remove the oil fill tube,
that can lead into removing the intake bolts so you can lift up the intake to remove the oil fill .
That rear seal is easily removable with the WB in place,
just stuff a rag under the seal as it can drop into the hole,
(this takes it to the water pump impeller,
and with a perfect roll can drop into one of ports to the block,
then you wont be able to remove it)
Use a long flat blade screwdriver pry the edge of the seal into its center then it will fall out of its bore.\
Be careful not to bend the seating surface of the T stat.
Thanks Mrmerlin. I have tried everything to remove that rear gasket as I really don’t want to remove the bridge but there is just not enough gasket to remove. It has deteriorated to the point that the housing surface has to be scraped clean. It’s like removing tar. I can’t see any other way but to remove the bridge so I can gain access to scrape that surface clean without damaging the gasket attachment surface
Do you have the replacement part in front of you to look at?
The black stuff sits on top of a raised lip that is proud of the block surface by about 1mm- you have to push this raised lip radially inwards to cause the seal to collapse. As Stan says a chunky flat bladed screw driver will work fine - you can use a small wedge of wood to pry off- I have a feeling I used the inner wall of the thermostat housing - just be careful not to bruise it.
Thanks. I do have the new gasket to look at and think I understand how it fits over that small lip. However when trying to pry it up to collapse on itself all I can get is what is shown on the attached pic. Everything comes off in much smaller bits then the one shown
I also have to use a small vac to vacuumed up the small pieces. I do have a rag stuffed in the bottom hole to prevent pieces falling further into the system
First of all, thanks to you all for the help with that thermostat rear seal. Using your guidance I finally got the seal out and replaced. New thermostat installed and drove with no leaks. However during the test drive in Floridas 95 degree heat and average stop and go traffic the car ran cool and great until I shut it off for about 45 minutes then headed home. On the trip the needle slowly climbed to about two needle widths past the last white mark but short of the red mark. I made it home, shut it off and left the car to cool. Then as just to check I went back to the car turned the ignition on did not start it put the air conditioner and blower on and the fans did not come on. I came out later when the car was cool and did the same test and both fans came on. So I am assuming they did not come on during the trip home thus the overheating. This is the second time he fans have not come on for the second already warm leg. Is there something about the fans coming on when the engine is cool and getting warm V’s coming on with an already warm or hot engine? FYI-Fan Power amp has been replaced as well as fuses, relays and circuit board cleaned and tested.
Here is a follow up to the previous. Went out this morning. Turned on ignition then blower then Ac. Both fans ran as expected. Went for a short 5 mile drive. Temp reading mid gauge(1990 S4 Auto). Turned car off for about 30 seconds then repeated test. Results= No fans. Top radiator hose 157 degrees bottom hose 153 degrees
Temperature results are meaningless on a car with the engine not running and measuring the hoses. The hoses insulate so you get a false reading- always shoot on metal surfaces as the average metal temperature will be close to the internal temperature. When the engine is not running the temperature across the radiator will quickly even out so best shot when coming in off a run, hop out of the car and with the engine running shoot the water bridge and the thermostat housing to have a chance of a meaningful result and also calibrate the measuring device against a known similar temperature [boiling water] to get some idea of accuracy.
As to why the fans are sporadically not running for sure needs to be resolved. Sounds as though the fan control unit could be playing up given you have changed out the fan power module. Short of testing with a known working module not sure what else could be done. Hopefully someone may have a bright idea!
Yes seems the suspects now are the temp sensor and the fan control unit (the one under the passenger side sill cover). The fan control units seem very reliable and live in a protected environment - so I'd start with the cooling fan temp sensor - maybe it goes wonky when warmed up - so you'd want to be testing it hot - more difficult!
07-25-2023, 12:04 PM
