Thermostat Issues
10/17/20, 08:54 PM
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Thermostat Issues
Hey, first post on here and I'm hoping someone can help me out.
So I bought a 1998 3.8L Mustang just a few months ago from some guys who run a car shop about 2 weeks ago it gave me a check engine light and a code for a thermostat issue, after getting the light I would notice that the engine stayed cold and never got up to temp. After replacing the thermostat (which I verified is facing the right way and tested it beforehand to make sure it wasn't bad) it ran fine up until a few days ago when it would spend the first 10-15 minutes of my drive in cold, then it would slowly rise to overheating temp. I'm not sure where to go from here.
I'd also like to add that when I replaced the thermostat, there wasn't one there in the first place...there's no way it could have been there because I know for a fact I didn't see one when I removed the housing. I drove it a solid 900 or so miles before the check engine light came on and the engine heated itself just fine up until I replaced the thermostat.
Thanks
So I bought a 1998 3.8L Mustang just a few months ago from some guys who run a car shop about 2 weeks ago it gave me a check engine light and a code for a thermostat issue, after getting the light I would notice that the engine stayed cold and never got up to temp. After replacing the thermostat (which I verified is facing the right way and tested it beforehand to make sure it wasn't bad) it ran fine up until a few days ago when it would spend the first 10-15 minutes of my drive in cold, then it would slowly rise to overheating temp. I'm not sure where to go from here.
I'd also like to add that when I replaced the thermostat, there wasn't one there in the first place...there's no way it could have been there because I know for a fact I didn't see one when I removed the housing. I drove it a solid 900 or so miles before the check engine light came on and the engine heated itself just fine up until I replaced the thermostat.
Thanks
10/18/20, 12:00 PM
#2
THE RED FLASH ------ Master-Moderator
Doesn't make any sense to me that your engine wouldn't overheat without a thermostat in it, especially when a check engine light and code came up.. As for the engine overheating when you installed the thermostat, did you install the correct temp stat as in 190 or 180 degree or did you install a lower temp 160 degree stat, if in fact you installed an aftermarket/lower temp 160 degree stat? that may possibly be the reason for your engine/overheating issues. Anyhow, just a thought you may need to consider 
On a lighter note, welcome to TMS 
On a lighter note, welcome to TMS
Last edited by m05fastbackGT; 10/18/20 at 07:05 PM.
10/18/20, 03:11 PM
#4
THE RED FLASH ------ Master-Moderator
So perhaps the engine is better off without running a thermostat if it takes longer to reach operating temps and also prevents the engine from overheating
Last edited by m05fastbackGT; 10/18/20 at 03:25 PM.
10/18/20, 04:18 PM
#5
Legacy TMS Member
No, that'll mess up the fuel economy and emissions, m05. May even cause a premature catalytic converter failure. You really don't want to do that. It needs proper fixing.
OP, welcome to the forums!
Forgive if I state obvious-to-you things, your post doesn't tell me what you've done or not, know or not. Pressing onwards...
You do know about the burping of the system, right? You must do the proper burping of the system if the coolant system is opened up...
http://www.njtacc.com/tech/coolant_refill.html
I bet that fixes it. What I'm betting is happening is this: Air in the system at the intake. Which is where the thermostat and the sensor both live. They can't get proper temperatures, and due to the system having the air in there, it causes the rest of the fluid to not flow, trap heat, and overheat the engine. The coolant boils, that steams the sensor, and the car's reading hot, because it is. There *cannot* be air in the system. It must be purged. Hence the goofy procedure. It is recommended you also jack the front of the car up a little to help the air get out of the vent tube when filling. Not so much for draining, but then I'm just pulling the lower radiator hose outright, just get it over with.
The reason is thus: SN95s have lowered hoods in front for aerodynamics which cause the intake to be the highest point in the coolant system. Air will get trapped up there by filling it at the radiator as normally done. So they put a pipe with a screw in it to vent the air when filling it up. '05s and up, and previous models before the SN95s don't have this problem, their systems have a high point at the fill inlet. Either reservoir or the radiator cap. This is an interesting problem of the SN95 Mustangs, both V8 and V6. It was also a problem for the MN12 platform (TBird, Cougar) and FN10 (Mark VIII), among a few others I'm sure. Those sleek hood fronts meant low radiator tops, and so the bubbles happened unless you did it right.
Otherwise, well, I priced out a radiator, water pump and gaskets, thermostat (195 degree OEM temp) and gaskets, and heater core for only 150 bucks at rockauto.com for your car. If you were to replace all those, you'd have everything but pipes/hoses replaced and that would definitely fix it... not that I'm saying to do that, but I'm saying you might have to do that, so might as well do it all if you're doing it at all, although I'd hold off on the heater unless I absolutely had to do that... miserable job, honestly, on that car... or any Mustang... or any car, frankly, of the 80s and up...
Dang, that was a long sentence. Sorry.
But if the burping thing doesn't fix it, you're gonna need to probably just redo the whole thing, I'm thinkin'. Which is why I'm hopin' it is the burping.
The other thing that comes to mind is... are you losing coolant somewhere? Maybe in the exhaust or in the oil? Or a pipe, like at the firewall to the heater? The pipe leaking can put air in the system and cause this too. Anywhere else, like the engine... well, let's hope not, shall we? Yes, we shall.
I do hope that helps! And again, if I mentioned something you already knew/did well, darn. How was I supposed to know?
Good luck, let us know!
OP, welcome to the forums!
Forgive if I state obvious-to-you things, your post doesn't tell me what you've done or not, know or not. Pressing onwards...
You do know about the burping of the system, right? You must do the proper burping of the system if the coolant system is opened up...
http://www.njtacc.com/tech/coolant_refill.html
I bet that fixes it. What I'm betting is happening is this: Air in the system at the intake. Which is where the thermostat and the sensor both live. They can't get proper temperatures, and due to the system having the air in there, it causes the rest of the fluid to not flow, trap heat, and overheat the engine. The coolant boils, that steams the sensor, and the car's reading hot, because it is. There *cannot* be air in the system. It must be purged. Hence the goofy procedure. It is recommended you also jack the front of the car up a little to help the air get out of the vent tube when filling. Not so much for draining, but then I'm just pulling the lower radiator hose outright, just get it over with.
The reason is thus: SN95s have lowered hoods in front for aerodynamics which cause the intake to be the highest point in the coolant system. Air will get trapped up there by filling it at the radiator as normally done. So they put a pipe with a screw in it to vent the air when filling it up. '05s and up, and previous models before the SN95s don't have this problem, their systems have a high point at the fill inlet. Either reservoir or the radiator cap. This is an interesting problem of the SN95 Mustangs, both V8 and V6. It was also a problem for the MN12 platform (TBird, Cougar) and FN10 (Mark VIII), among a few others I'm sure. Those sleek hood fronts meant low radiator tops, and so the bubbles happened unless you did it right.
Otherwise, well, I priced out a radiator, water pump and gaskets, thermostat (195 degree OEM temp) and gaskets, and heater core for only 150 bucks at rockauto.com for your car. If you were to replace all those, you'd have everything but pipes/hoses replaced and that would definitely fix it... not that I'm saying to do that, but I'm saying you might have to do that, so might as well do it all if you're doing it at all, although I'd hold off on the heater unless I absolutely had to do that... miserable job, honestly, on that car... or any Mustang... or any car, frankly, of the 80s and up...
Dang, that was a long sentence. Sorry.
But if the burping thing doesn't fix it, you're gonna need to probably just redo the whole thing, I'm thinkin'. Which is why I'm hopin' it is the burping.The other thing that comes to mind is... are you losing coolant somewhere? Maybe in the exhaust or in the oil? Or a pipe, like at the firewall to the heater? The pipe leaking can put air in the system and cause this too. Anywhere else, like the engine... well, let's hope not, shall we? Yes, we shall.
I do hope that helps! And again, if I mentioned something you already knew/did well, darn. How was I supposed to know?
Good luck, let us know!
Last edited by houtex; 10/18/20 at 04:21 PM.
The following users liked this post:
m05fastbackGT (10/18/20)
10/18/20, 07:03 PM
#7
THE RED FLASH ------ Master-Moderator
10/19/20, 03:35 PM
#8
Legacy TMS Member
Yessir, just tryin' to help!
Just to flesh this out a little... the whole thing is efficiency of the cylinder's combustion. If the cylinder is cold, unburnt fuel happens, so that's where the catalytic converters come in as potential failures over long time, as well as the emissions of course. Maybe some carboning up of the valves. If the cylinder is too hot, then preignition happens and you could damage the engine (something I forgot to mention, sorry.) Then as the computer starts to try to adjust for all that, either way, your fuel economy goes in the tank straight away. Well, no it goes *out* of the tank... you know what I mean.
AND it could kill the engine trying to save it, if it goes too lean and burns the cylinder up.
Thermostat is really important, turns out. Not like the ol' carburetor days where you could just take the stupid thing out and the engine could still be tuned, 'cause not efficient anyways, and who caree about emissions back then, right? Cold engine means long lasting engine!
Not today, nosir. Good way to kill something now. Yay engineers.
Just to flesh this out a little... the whole thing is efficiency of the cylinder's combustion. If the cylinder is cold, unburnt fuel happens, so that's where the catalytic converters come in as potential failures over long time, as well as the emissions of course. Maybe some carboning up of the valves. If the cylinder is too hot, then preignition happens and you could damage the engine (something I forgot to mention, sorry.) Then as the computer starts to try to adjust for all that, either way, your fuel economy goes in the tank straight away. Well, no it goes *out* of the tank... you know what I mean.
AND it could kill the engine trying to save it, if it goes too lean and burns the cylinder up.Thermostat is really important, turns out. Not like the ol' carburetor days where you could just take the stupid thing out and the engine could still be tuned, 'cause not efficient anyways, and who caree about emissions back then, right? Cold engine means long lasting engine!
Not today, nosir. Good way to kill something now. Yay engineers.
Last edited by houtex; 10/19/20 at 03:37 PM.
The following users liked this post:
m05fastbackGT (10/19/20)
10/19/20, 06:52 PM
#9
THE RED FLASH ------ Master-Moderator
Yep! was definitely thinking of the ol' school carburetor days for sure 
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