Best Thermostat brand for Hemi
- Thread starter nwjones18
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Swapped the water pump today. Pretty straight forward job on the Hemi. Aisin Water pump looked good. Was made in China and its entirely possible it is another reboxed Gates or GMB, no way to tell though. Drove around for quite a while and Aisin thermostat does a good job holding the truck right at the specified 203 degrees.
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Here is a little thermostat story. I had a 2018 Jeep GJ 3.6 in the shop one day for p0128 thermostat code and a leak at the thermostat plastic housing. I replaced the thermostat housing assy with a thermostat kit (housing w/therm already installed and o ring). It was a duralast (motorad in the box) because it was late on a Saturday and the Jeep dealer was closed and the customer was leaving for a trip Sunday. Everything seemed ok didn't leak and got up to temp as it should. The customer took their trip and came back with the comment that everything went well but everytime they accelerated hard or drive up an extended mountain pass the temp gauge would climb to the 3/4 mark - high but not in the red. As soon as they let off the gas or coasted the temp gauge immediately went back down to normal. This would happen constantly but never stayed high long and never overheated. When they got back, I could duplicate the condition every time. Hard accel for a good distance gauge up 3/4 (read 245 on scan tool) then ease up and the gauge was back down to the middle in no time. Got a new Mopar assy and compared it to the motorad......the motorad was approx 1/4" narrower in the neck. I think that was what caused the overtemp. Once the Mopar was in - problem never happed again. Also - even the steady cruise temp was 5-8 degrees higher then the Mopar.
Thank you so much. I will also add that in recent times we seem to be having to add more and more parts to the OEM only list.
I'm generally in the OEM only for Thermostat's camp as well, but at this point I figured the odds of getting a Motorad in the Mopar box were decently high, and at least I know the Aisin isn't a Motorad... My factory one was working fine and I kept it, but it has a rubber seal in it that is 10 years old at this point. Its also not hard to change so if I have issues I'll spring for the Mopar one. I'd generally say OEM only for the water pump as well, but a quick google will tell you the Mopar water pumps are nothing special longeveity wise on the Hemi's. Some get long life and some die at 30k miles. Mine made it 72k. I'll post back here if I have any issues in the future.
Just to throw in another county........
Thermostats were the very first thing I learned to "always go OE".
The jiggle pins in the equalization hole seemed always to be absent on aftermarket 'stats.
An emergency run to an Advance Auto Parts got me a 'stat for a Toyota which interfered with a casting surface and caused it to stick open.
However, the real kicker was that the vehicle's owner, a neighbor for whom I did a bunch of things, had installed an OBD reader which relayed to the internet, giving her alarm messages.
Nothing like a panic message from a 90 year old. The alarm rattled her good.
Thermostats were the very first thing I learned to "always go OE".
The jiggle pins in the equalization hole seemed always to be absent on aftermarket 'stats.
An emergency run to an Advance Auto Parts got me a 'stat for a Toyota which interfered with a casting surface and caused it to stick open.
However, the real kicker was that the vehicle's owner, a neighbor for whom I did a bunch of things, had installed an OBD reader which relayed to the internet, giving her alarm messages.
Nothing like a panic message from a 90 year old. The alarm rattled her good.
This. I'd sooner try Aisin or Calorstat than risk Motorad in an OEM box
Of the hundred or so cars, ATVs, tractors i've worked on, I can think of maybe two thermostat failures at most. The brand has never concerned me, only fitment. Usually i'll proactively replace the thermostat whenever water pump work is needed, maybe thats why i've seen little to no failures.
I just faced this decision on a Pentastar for a Journey. I wasn't opposed to OEM but my dealer wanted $101 and they said it's a week out?!?!
I finally decided on a Calorstat from RA. I wasn't thrilled to see MIC
but they cast their name into the housing. I think this is a nice touch to suggest it's not just off the same assy line as everything else. That said, it could be exactly the same as Motorad with a different housing -- I have no evidence either way.
I finally decided on a Calorstat from RA. I wasn't thrilled to see MIC
but they cast their name into the housing. I think this is a nice touch to suggest it's not just off the same assy line as everything else. That said, it could be exactly the same as Motorad with a different housing -- I have no evidence either way.
With pics below...
When I was recently researching a new thermostat for my 4.7L, my initial findings was that Motorad is the OEM supplier for Mopar and NAPA brand thermostats and that Motorad seemed to be a favorite among the commenters. It wasn't until later when I found people stating the opposite saying to avoid any Motorad thermostats. Anyway, it was too late, I've purchased and installed a Motorad Ultrastat. Guess I'll find out first hand. Will it be a great choice or should I have avoided it?
Cited: 4.7L Thermostat 180*
Cited: What Thermostat have you had good luck with?
When I was recently researching a new thermostat for my 4.7L, my initial findings was that Motorad is the OEM supplier for Mopar and NAPA brand thermostats and that Motorad seemed to be a favorite among the commenters. It wasn't until later when I found people stating the opposite saying to avoid any Motorad thermostats. Anyway, it was too late, I've purchased and installed a Motorad Ultrastat. Guess I'll find out first hand. Will it be a great choice or should I have avoided it?
Cited: 4.7L Thermostat 180*
Cited: What Thermostat have you had good luck with?
Nick1994
$100 site donor 2024
A few years back I went to the dealership for a thermostat for my ‘96 Jeep Cherokee. Went to install it and it was a Motorad, went to pull out the Auto Zone thermostat (Duralast boxed) I had in the Jeep and it too was an identical Motorad.
Thanks for the comment. So it would seem to me that hundreds of thousands of Mopar vehicles on the road were originally supplied from the factory with Motorad thermostats. If there was a high failure rate and countless warranty claims, Mopar would have switched suppliers and the info would have slipped out of these high failure rates. I haven't heard of that happening. On another note, I find it refreshing my UltraStat is Made In Israel and not China. Anyway, hopefully it works out. Fingers crossed.
OE. If not, OE specified temp.
Thanks for the comment. So it would seem to me that hundreds of thousands of Mopar vehicles on the road were originally supplied from the factory with Motorad thermostats. If there was a high failure rate and countless warranty claims, Mopar would have switched suppliers and the info would have slipped out of these high failure rates. I haven't heard of that happening. On another note, I find it refreshing my UltraStat is Made In Israel and not China. Anyway, hopefully it works out. Fingers crossed.
Just because Motorad is the OE supplier doesn't mean their aftermarket thermostats are worth anything
OE Motorad thermostats are really designed by the OEM, just manufactured by the supplier (Motorad in this case).
A few people on here have gotten aftermarket Motorad thermostats in a Mopar box, and they are just as bad as the identical ones from the parts stores.
Motorad bought, then killed, Stant's aftermarket line.
Honestly, an Aisin from China is better than a Motorad from any country. For some cars, you can get a Facet from Italy.
It's been a LONG time since I had occasion to buy an aftermarket thermostat, but the Robert Shaw I put in my old diesel Ram was very, very impressive. I've never seen a larger wax motor on a thermostat.
The last stat I replaced was when I did the cooling system overhaul on my GX. I went OEM toyota.
The last stat I replaced was when I did the cooling system overhaul on my GX. I went OEM toyota.
You're probably fine there. Israel COO is promising. Pretty sure Ultrastat is old Stant terminology for their better stuff, but whether this one was built with the same tooling to the same specs is impossible to know.Thanks for the comment. So it would seem to me that hundreds of thousands of Mopar vehicles on the road were originally supplied from the factory with Motorad thermostats. If there was a high failure rate and countless warranty claims, Mopar would have switched suppliers and the info would have slipped out of these high failure rates. I haven't heard of that happening. On another note, I find it refreshing my UltraStat is Made In Israel and not China. Anyway, hopefully it works out. Fingers crossed.
I have no doubt the OEMs hold Motorad's feet to the fire, but at some point (time/age) they'll cut costs and allow the bottom end stuff into a Mopar box. Why stock high end thermostats for a discontinued, no-longer-under-warranty engine architecture when you could put a $2 thermostat in a $30 box?
FWIW Aisin thermostat is still doing fine. I thought it was acting up for a little bit but figured out the active grill shudders also control the engine temp and open/close as they see fit on the highway
Can anyone identify the thermostat pictured below? It's the one I pulled out of my 4.7L Dodge. It was installed by a local mechanic shop in 2017. Could it be an original pre-Motrad Stant?
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- Mar 4, 2026
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Get a fail/Open. They cost a bit more but are worth their weight in gold the first time you have a failure. It is a Hemi so not a huge deal since you can always deck the block and surface the heads but for anything with OHC and all aluminum with VVT and such prevent the over heat at all cost.
Now what almost no one does today is pre test the thermostat. As a young apprentice we you would not dream of this. So hot plate, beaker, water enough to cover the thermostat, thermomater(sp) and either some string to tie around the part or a pair of long needle nose pliers. Bring the water to the same temp that part should open at not much more you do not want to damage the wax slug. So if it is 195° get the water to that temp if it is made to open at 180° get the water to that. Lower the part into the water and wait to see the tiny disc in the center open out of the way. Once it opens remove it and let it cool. Now you know the part you are installing is good and opening at the correct temp. If not get another one!
Make sure you install the air bleed in the same postion as the origanal that is the tiny hole in the outer rim with what looks like a brass triangle or wand or bell striker bit sticking through that tiney hole. You can jigle it. That is there to keep air pockets from building up on the one side and getting trapped.
Now what almost no one does today is pre test the thermostat. As a young apprentice we you would not dream of this. So hot plate, beaker, water enough to cover the thermostat, thermomater(sp) and either some string to tie around the part or a pair of long needle nose pliers. Bring the water to the same temp that part should open at not much more you do not want to damage the wax slug. So if it is 195° get the water to that temp if it is made to open at 180° get the water to that. Lower the part into the water and wait to see the tiny disc in the center open out of the way. Once it opens remove it and let it cool. Now you know the part you are installing is good and opening at the correct temp. If not get another one!
Make sure you install the air bleed in the same postion as the origanal that is the tiny hole in the outer rim with what looks like a brass triangle or wand or bell striker bit sticking through that tiney hole. You can jigle it. That is there to keep air pockets from building up on the one side and getting trapped.