Best part number/item for thermostat gasket?

potshotscott

Registered User
So I've bought two different thermostat gaskets locally here at AZ and O'Reilly's and they just don't match the Tstat housing openings like they're supposed to. The holes "sort of" line up. Does anyone have a good source for thermostat gaskets that work/fit correctly?
 
I prefer Fel-Pro #35459 ...light blue so you can't miss it. https://www.autozone.com/cooling-he...l-pro-thermostat-gasket-35459/225119_199430_0 - Bolt holes and bypass hole line up correctly, but the hole for the thermostat overlaps/is smaller, helps to hold it in the housing during assembly.

I coat it and the thermostat housing flange with blue RTV, let it sit for a few minutes, then assemble, waiting overnite before refilling w/coolant and run testing.

If you're having issues sealing, be sure the flange is flat, including around the bolt holes. Don't overtorque when assembling, I use 22 ft. lbs.
 
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I'd always been a fan of using the gaskets, but that's changed. Twice (once with my SC) the thermostat housing I had just installed weeks earlier started leaking. In both cases, the RTV did not fail. The gasket was actually saturated and wicking the coolant out. The one I had installed in the SC was Felpro. I've since started using RTV only, snugging the bolts just enough for the RTV to spread evenly, and then tightening the bolts hours later or the next day. That keeps the RTV from squeezing out so it can become a nice gasket before being compressed. I've never had a failure since, even with warped housings.
Side note: every time I got a thermostat gasket for my SC from the part stores, it was the wrong shape. They gave me the right part number but the gasket was clearly for a different car.
 
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Since I tried just RTV twice I went the FelPro route. I put a film of RTV on the gasket and mated it to the thermostat housing. I let it set for 2 hours and then put a thin coat on the gasket/housing and mated it to the car. Waited 24 hours to fill and all is well. I really like the drain cock on the radiator since its easy to put a flex-tube on the spigot and drain into a clean milk jug. Take out about 1 liter of fluid and the thermostat housing and intake are dry. Easy stuff there. I used a coffee filter to make sure I wasn't putting anything nasty back in.

Thanks for the advice guys.
 
I hope everything works out for you, but keep an eye on it. It took weeks before my Felpro gasket absorbed enough to complete the coolant's escape path and start dripping very slowly. When I fixed it for the last time, the housing came off easily as the coolant drenched gasket separated all the way around, still perfectly adhered to the RTV on the intake and the housing. I will say, the Felpro gasket took much longer to fail than the other brand we used at work. Otherwise, Felpro does make great stuff.
 
I hope everything works out for you

Done right, I'm sure it will.

Heck, I knew an old salt that hated gaskets, adhesives -and- fasteners...he'd just weld things shut and dare them to leak ;)

Thankfully, gaskets and adhesives have advanced over the ages. Any trouble sealing things up these days, you've got bigger issues.
 
Thanks - oddly enough my code 118 is back - brand new sensor too. From here I need to check Voltages and resistance of the sensor. I still have all your notes from a few weeks ago. The sensor keeps the car from starting on occasion - quite annoying but it's cheating the computer to flood the engine with fuel... very odd indeed.
 
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Code 118. The Coolant Temp Sensor is sending (or the PCM is receiving) the wrong Voltage. It really affects the mixture of the car when starting warm. I have the EVTM so I should be able to solve this one in a weekend.
 
I did see this thread and recall seeing another one where you might have referenced your actual Voltage drops. I need to go back in the EVTM to what the source Voltage should be. I'm on a new (refurb) PCM. Perhaps the old PCM was fine and I have corrosion as you suggest. Either way I should be able to dig in later today. Thanks KMT.
 
Ref. voltage is 4.00v ~ 5.00v - use caution when testing.

I eventually found my issue by checking at the ECT...was low there, and I was ready to break out my backup PCM, then I checked at the main connector back on the harness. Was good going in, low coming out. I had already checked the signal out of the ECT, and since it didn't jive with engine temp, I replaced it, but when nothing changed, I finally sniffed ref. volts. and started backtracking. Next time I'll start by verifying ref. volts at different sensors/components first.

I like to think that since the ref. voltage is shared across different sensors/components, that if it is the PCM's base fault, they will all complain/throw codes, but again, in my case, no codes, just late fan turn-on.

The corrosion in the main harness was affecting more than just the ECT, I think - guess I put too much faith in no codes, but I have to wonder what else was marginalized, from MAF to injectors to ACT, etc. In any case, I've corrected the issue and verified ref. volts at the rest of the affected circuits.

And don't forget all the grounds, too.
 
Does the 5V come directly from the PCM? I appears to in the EVTM. Wondering if it goes through the IRCM first... tearing it down now.
 
Strictly via the PCM as i understand it. I don't recall any direct connection between the ECT and IRCM, otherwise.

AFAIK, the PCM sends out the ref. voltage which the ECT uses to send a signal that varies based on coolant temp, back to the PCM, which then (among other things based on engine temp) executes strategy/triggers the IRCM, which then lights the fan, based on.
 
Well if that's the case then the ECT is a crucial part of the system. I did find my problem. I must have bent a pin probing it with my VOM several months ago when i was looking at my supposed PCM issue. I didn't have 5V and my continuity was fine between that connector block and the sensor itself. I bent the pin closed slightly and got the circuit working. Funny thing - the check engine light was still on. I let it warm up in the driveway and then took it for a short drive. For some unknown reason I paused, shut down the car and it would not start back up - exact same symptoms I've been fighting all summer. Left the car and walked home (not far). Went back just now and it fired right up. CEL code cleared too. Odd as heck if you ask me.

At this rate I've worked on it more than I've driven it. I'm really considering listing it for sale. I'm done tinkering - I'd like something fun to drive that requires less maintenance. The "cool" appeal of keeping this car on the road has lots its luster.

Thanks for the help again Ken

Anyone near Denver want a rust free 94 SC Auto?
 
...must have bent a pin probing it with my VOM several months ago when i was looking at my supposed PCM issue.

Feel your pain. I had a fresh one that sunk a pin when the connector was in place. It would barely make contact...sometimes - it was new so i kept looking elsewhere. These days, if there is any question surrounding the ECT I just warranty it for a new one and move on. I've got a 1/2 dozen old ones pulled from wrecks and none of them bench test the same.

Interesting discussion here, I think: https://www.underhoodservice.com/diagnostic-solutions-engine-coolant-temperature-sensors/
 
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Sorry to dig this old thread up but my problem persists. Ken, you've been very helpful with this. Here's my problem - quite frankly these wiring diagrams are too simple. Meaning they're not descriptive enough. Aircraft manuals in the Navy go into full detail on what is expected on each pin of a connector. In the example attached all that is mentioned is Signal Return (PCM Pin 46) and ECT Signal (PCM Pin 7). I have the EVTM and can chase all of that no problem. I guess the crazy question I have is this; Is the signal return the 5VDC line while the ECT Signal is the thermistor adjusted Voltage heading back to the PCM? I have to believe it is. Although what's odd is that with the connector disconnected from the sensor I read about 5V on EACH PIN. That quite simply can't be correct in my mind unless I'm crazy. Starting to think I have another issue but I have to wait until the weekend to dig in.

Again - sorry to beat this thread up again but does anyone have an accurate account for what Ford means when they use the term "Signal Return"? In the EVTM it's common to a BUNCH of sensors - I highly doubt its anything other than a 5V feed into each sensor.

Thanks in advance.View attachment 94SC Schematic_Block Diagram.pdf
 
In the example attached all that is mentioned is Signal Return (PCM Pin 46) and ECT Signal (PCM Pin 7). I have the EVTM and can chase all of that no problem. I guess the crazy question I have is this; Is the signal return the 5VDC line while the ECT Signal is the thermistor adjusted Voltage heading back to the PCM? I have to believe it is. Although what's odd is that with the connector disconnected from the sensor I read about 5V on EACH PIN. That quite simply can't be correct in my mind unless I'm crazy. Starting to think I have another issue but I have to wait until the weekend to dig in.

Again - sorry to beat this thread up again but does anyone have an accurate account for what Ford means when they use the term "Signal Return"? In the EVTM it's common to a BUNCH of sensors - I highly doubt its anything other than a 5V feed into each sensor.

Correct, simply a low voltage baseline. That's the 5v DC ref. out of the PCM/EEC and the input to several sensors.

Just to be sure we're on the same page, the 'signal'* is the output from the sensor, fed into the PCM/EEC. DO NOT ATTEMPT TO READ ref. voltages with the related connector(s) unplugged from their sensors. They -must- be read with the system live, connected and with sensor loads in place Trying to check reference voltage by unplugging the connector is a no-go.

Always backprobe, then check key on. DVOM recommended so you know it's value and not just that it's hot. This can be critical so you don't get fooled into relying on an out-of-spec reference voltage.

I read the output off the ECT via backprobing as well. After confirming 5v ref. in (might be as low as 4.5v actual), you would expect to see a voltage drop coming out from 3.51v at 50°, to 0.46 at 212°

LG/Y is signal out at ECT. This goes to the EEC. Backprobe it to check when engine runs and heats up. Ground black lead off meter to complete circuit to test. If meter does not auto range, be sure to use lower scale to read DC 5v and less. Have to admit I've never paid much attention to ref. voltage in the past. Been trying to adopt better elect. troubleshooting skills, including using a an o'scope for testing. The more you learn about sophisticated auto circuitry, the better chance you have of keeping cars like the SC going, I guess. A test light will get you only so far these days.

About your diagram... 46 should be the 5v ref. (again, used by several circuits) ...beyond me why that diagram calls it SIG RTN (return), tho. I'm calling radishes on that...

7 is the (adjusted) output from the sensor/thermistor. What are 46 & 7 named in the PCM's/EEC's connector face/pinout in the EVTM?

*Note my habit is to refer to sensor output as a 'signal' (variable), and ref. voltage as a 'feed' (constant), but that's just me, so don't be confused. The factory diagrams call 7 'feed', opposite my habit. No matter, we both agree/consider 7 as the ECT's adjusted output that the EEC uses (among other inputs) to decide fuel strategy.

Sorry if I'm repeating myself here.

Ken
 
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