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Yo basically I got a 98 z28 6 speed. Full stock rebuilt at 94k miles. My issue is my car is over cooling when I go past maybe 40mph. It’s got manual fans using Casper electronics 109068 fan module. It’s also got an aluminum radiator and new thermostat and thermostat housing.. at 60mph with fans off I’d go from 210 f to like 180 and below after only 5min… the longer I drive at high speeds the colder the car gets.. I’ve tried to remove the manual fan switch module but then my fans never kicked in… and now to top it all off after replugging the fan module only the high setting works and the low setting doesn’t work lol. Anyways I’d appericate any ideas as to why my car isn’t heating properly. I also forgot to mention it takes forever to warm up.. I’ve had this problem every since I got it and I thought the new thermostat would fix it but it didn’t… thx
What thermostat are you running. OEM stat shouldn’t let the engine get any cooler than 184 degrees I think.
Factory t-stat for these engines was an 86°C (187°F) unit. So no matter how fast the fans blow or how early they cut on, the engine won't run cooler than that unless it's being operated in very cold conditions, or the t-stat is stuck open, or it has been replaced with a colder unit, or it has been removed completely. I see you mentioned having a new t-stat & housing, but you didn't mention what temp it was rated for.
If it's very cold outside, and the engine bay is well vented, and/or you have the heater running (HVAC fan blowing), then the engine could cool below the rated t-stat temp even if everything with the t-stat itself is working fine. But it sounds like your condition occurs pretty much at all times during sustained speed cruise, though we still don't know if that suggests a problem without knowing the rated temp of your new t-stat.
Factory t-stat for these engines was an 86°C (187°F) unit. So no matter how fast the fans blow or how early they cut on, the engine won't run cooler than that unless it's being operated in very cold conditions, or the t-stat is stuck open, or it has been replaced with a colder unit, or it has been removed completely. I see you mentioned having a new t-stat & housing, but you didn't mention what temp it was rated for.
If it's very cold outside, and the engine bay is well vented, and/or you have the heater running (HVAC fan blowing), then the engine could cool below the rated t-stat temp even if everything with the t-stat itself is working fine. But it sounds like your condition occurs pretty much at all times during sustained speed cruise, though we still don't know if that suggests a problem without knowing the rated temp of your new t-stat.
sheesh you’re right, I thought I got a “stock” thermostat but once I check autozone I realized I most likely got a 160f… I’m probably gonna switch it out for a 187 assuming it’s better for my motor considering I’m fully stock and fresh rebuild. My only other question is any idea how I could go back to stock fans. When I unplugged the Casper fan switch and replugged the harness without it. The fans never kicked on.. I’m only asking because for some reason after replugging my fan switch only the high setting works.. I installed my engine myself but I’m not very electrical savvy to know how to diagnose wires… the fan switch worked fine before I just unplugged and replugged it smh. Also really appreciate the help
My only other question is any idea how I could go back to stock fans. When I unplugged the Casper fan switch and replugged the harness without it. The fans never kicked on.. I’m only asking because for some reason after replugging my fan switch only the high setting works.. I installed my engine myself but I’m not very electrical savvy to know how to diagnose wires… the fan switch worked fine before I just unplugged and replugged it smh. Also really appreciate the help
Not sure what to say about the fan switch. Perhaps something failed during the process of removing/reinstalling, maybe a marginal solder joint inside the switch or brittle wire in the switch harness was jarred just enough to cause a contact issue, etc.
As for the stock fan settings though, assuming nobody ever reprogrammed them (which is quite possible, since they were using the fan switch), the stock settings are as follows:
Low speed on at 227°F/off at 218°F
High speed on at 235°F/off at 228°F
As you can see, those numbers are quite high. It would take some time for the fans to automatically engage with the stock settings, so it's very possible that they still work fine without the switch and that you just didn't let it get warm enough to see them come on.
The 1998 temp gauge is more functional than the '99+ version, but it's still not 100% accurate. So you would need a scanner or aftermarket gauge to really know the exact temp (and whether or not the fans are working per stock programming).
Not sure what to say about the fan switch. Perhaps something failed during the process of removing/reinstalling, maybe a marginal solder joint inside the switch or brittle wire in the switch harness was jarred just enough to cause a contact issue, etc.
As for the stock fan settings though, assuming nobody ever reprogrammed them (which is quite possible, since they were using the fan switch), the stock settings are as follows:
Low speed on at 227°F/off at 218°F
High speed on at 235°F/off at 228°F
As you can see, those numbers are quite high. It would take some time for the fans to automatically engage with the stock settings, so it's very possible that they still work fine without the switch and that you just didn't let it get warm enough to see them come on.
The 1998 temp gauge is more functional than the '99+ version, but it's still not 100% accurate. So you would need a scanner or aftermarket gauge to really know the exact temp (and whether or not the fans are working per stock programming).
really appreciate the help, ya naw i let the car get pretty hot, maybe 230 but i guess it is possible i didnt let it get that high, and might i jus say sheesh on at 227??? wow def gonna stick to manual fan switch lmao. and ya i used a expensive obd2 scanner to monitor my temps once and the stock gauge was pretty accurate. Once again thx for the help defiantly helped a lot!
really appreciate the help, ya naw i let the car get pretty hot, maybe 230 but i guess it is possible i didnt let it get that high, and might i jus say sheesh on at 227??? wow def gonna stick to manual fan switch lmao. and ya i used a expensive obd2 scanner to monitor my temps once and the stock gauge was pretty accurate. Once again thx for the help defiantly helped a lot!
Glad to help.
Just an FYI, but you have options other than just a fan switch if you want cooler settings. Custom tuning (such as HP Tuners software, or even handheld devices) can allow you to change the factory fan setting to something more to your liking. Then you wouldn't need to worry about the switch failing or operating incorrectly, everything would function just as it did stock, except at the (new) lower settings. If you don't want to buy the software just for this, most performance shops (or mail order tuning specialists) offer a basic tune option to cover things such as cooling fan changes (at a much cheaper rate than a full dyno tune or buying the program yourself).
Just an FYI, but you have options other than just a fan switch if you want cooler settings. Custom tuning (such as HP Tuners software, or even handheld devices) can allow you to change the factory fan setting to something more to your liking. Then you wouldn't need to worry about the switch failing or operating incorrectly, everything would function just as it did stock, except at the (new) lower settings. If you don't want to buy the software just for this, most performance shops (or mail order tuning specialists) offer a basic tune option to cover things such as cooling fan changes (at a much cheaper rate than a full dyno tune or buying the program yourself).
this sounds great, but i have terrible news lol, i just took apart the thermostat and found out i already had a 187f thermostat which was new… so now i’m confused as to why i was running below 187f at faster speeds. any ideas what could cause that?
03-05-2023, 07:10 PM
Manual fan switch/over cooling 
