Thermostat - 170/180/192

[Aonghus]

I did a search but didn't see any reference to the 192° thermostat from Motorad, link below.

 

I've gathered these vg30e engines like to run a bit on the hot side and there's quite a few examples of the 170° thermostat causing some issues with running . It seems the 180° is preferred.

 

But is 192° even better? Anyone have experience with it?

 

Once it's open at full operating temp it shouldn't make any difference which one you have. I would expect better warm up with the 192° or better for short trips around town or better on cold winter days...

 

All input welcome!

 

https://motorad.com/part/268-192/

 

Edited March 10 by Aonghus
Corrected title

[adamzan]

The 170F (76.5C) is what they all came with originally. I personally found that one a little too cold here in Ontario Canada during the winter time. Basically, it could barely keep the window de-iced and my feet warm when the temps dipped below -15C, especially on the extreme wind chill days. In doing some testing, I found the coolant temp barely stayed at 170F once it opened when driving in stop and go traffic, because these older style ones just tend to stay open unless it goes way cold, a temp solution was covering the rad with cardboard to block some airflow. You can test the t-stat in a pot of hot water. I swapped over to a 180F (82c) when doing my water pump and it made a decent difference, imo this is what they should have put in at the factory, the later VG33E (not supercharged) in the Xterra came with that one... The 192F (89C) was never a factory option and has only been available for the last few years. I don't know anyone that has tried it, though. It's still well within the normal operating temp so I don't see it being a big issue. 

 

These trucks aren't exactly known for overheating in my experience, so it should not be a problem provided your cooling system has been well maintained and the rad isn't full of scale. In 20+ years of owning a few of these trucks, the only time I had issues running warm were with a radiator that was full of mud. My 2.0 VW motor has a 190C stat originally, that thing has the best heat out of all of our cars!

Edited March 10 by adamzan

[Aonghus]

Thanks Adam! 

Our Tahoe takes a 195F stat if I'm not mistaken. Like you said, still well within normal operating temps. 

 

I think we'll give it a go when we do the water pump and timing belt. At that point we'll also flush everything and put new coolant in and hopefully get a decent idea on the health of the cooling system. It looked "clean" through the radiator cap but you can't see very much there. 

 

It seems like this rig was decently maintained in stock condition. Nothing is modded or upgraded but it's more or less in good condition considering its 311K miles. So here's hoping!

[gamellott]

I was under the impression that almost all computer controlled engines had the 195 degree thermostat. But... I have been wrong before. I think I replaced that when I did the heads, but I cannot remember which one I got... I probably defaulted to 195 if there was even an option...

[adamzan]

The hotter they run (within reason) the more efficient they are.

[Slartibartfast]

I just stumbled across some info on the 190F thermostat. It does exist, but Nissan warns of cats and dogs living together if it's used in a VG.

 

The problem with the 190F thermostat is that the VG does not run at the temperature of its thermostat. The VG's thermostat is located on the lower rad hose, the cold end of the system, so the engine actually runs 10-15C hotter than its thermostat. Nissan's target for max engine temp is 90C (194F). 76.5C (170F) plus 15C is right on target at 91C. 82C (180F) plus 15C is pushing it at 97C, but apparently Nissan was comfortable with this, because NTB94-020 recommends swapping in a 180F thermostat to help the heater keep up with winters on Hoth (like Adam did), and (as Adam noted) they later spec'd 180F thermostats for the VG33E. 88C (190F) plus 15C is 103C, and apparently that's out of Nissan's comfort zone, because they warn that it could cause overheating, detonation, engine damage, computer trouble, and a voided warranty. 

 

The 190 thermostat was used in earlier (pre-VG) Nissan engines. They had the same 90C/194F max temp target, but their thermostats were on the upper rad hose, so they didn't have that 10-15C offset to factor in.

 

TL;DR: 170 is stock, 180 is OK, and 190 is not recommended.

[gamellott]

That's some good info to know. Again, it's been a hot minute. I don't recall what I put in there. I don't know if there was even an option when I got it. It's kinda proprietary compared to others in my experience. Looking at Rock Auto, all 3 are offered, but it does state that 170 is OE. 

[Slartibartfast]

I'm 90% sure I put a 170 in my VG30 when I had it apart. I have noticed it struggling to hit temp when it's real cold out, but I think I remember it doing better when the tstat was new, so it might just be aftermarket junk that's on its way out out after 30k miles. I bought a 180 tstat from Nissan for the VG33 to see what that does. It'll probably be summer by the time I get that engine in the truck, so I'll know pretty quick if 180 was a mistake.

[adamzan]

Mine never runs hotter than 170 or 180 unless it's mid July in stop/go traffic with the air con running. In the winter it barely holds 170F on my VG33ER Xterra which is the same engine. Where you both live 180F is probably a good compromise. The 192F on rockauto was never available until recently, and I've been driving a wd21 since the early 2000s. Back then it was 170/180 only... Where did you find this info?

 

The VG33 in the r50 was a 170 too, but the Xterra they spec a 180 unless supercharged (which calls for a 170). Not that 10F is going to do that much for pinging.

[Slartibartfast]

12 hours ago, adamzan said:

Where did you find this info?

 

This TSB.

 

The 190 tstat that the TSB says not to use was for unspecified earlier models. I have no idea why Motorad is listing one for VG applications now. Maybe there's a demand from people who don't know how the cooling system works. Or maybe the increase in heat across the engine is not as high as Nissan expected, as seems to be the case with yours. (Or maybe the increase the TSB is talking about is more of a worst-case-scenario, assuming hard use in hot weather.)

 

Everything I've checked says the VG R50s ran 180 tstats. The '97 R50 FSM specs a 180. This listing shows a 180F/82C tstat as fitting '98-'04 Fronty (w/o supercharger), '00-'04 X (w/o super), '96-'01 R50, '93-'01 Quest, and '89-'94 Maxima.

 

The TSB above says to use the 180 from a Quest or a Maxima, which makes sense, as those are the only vehicles on that list that were in production when the TSB was written in '94.

 

How are you logging your temps?

[adamzan]

On the WD21 I used one of those laser thermometers at the upper coolant neck. On the Xterra I can see it in the bluedriver scan tool in live data.

 

Regardless, the heater barely holds up even in -15C around here.

[Aonghus]

Loving all this info! 

I see what you mean with the tstat on the cool side. So that must change the "when it's fully open" part of the thought process?

[Slartibartfast]

4 hours ago, Aonghus said:

So that must change the "when it's fully open" part of the thought process?

 

Maybe? Annoyingly, the manual does not explain why it's like this, just how to test and replace the components.

 

This thread suggests that regulating the cold side helps the engine warm up quicker and makes the engine temperature more stable. I guess the idea is that the engine raises the coolant temp pretty predictably, but the radiator drops it unpredictably, depending on air speed, ambient temp, humidity, aircon, auto trans temp, heat soak, grasshoppers, whatever else. So if you want a stable engine temp, it makes sense to put the thermostat between the biggest variable in the system (the rad) and the thing you want stable (the engine). And when it's warming up, and the lower rad hose is cold, I assume that cold water coming in will help keep the tstat closed for longer, versus a hot-side tstat that only sees the hottest water in the engine.

 

Looks like Ford's Coyote V8 and some GM LS engines use cold-side tstats, too. I did some reading on a Mustang forum, and found some of those guys talking about a difference in design between the tstats themselves (beyond just the temperature rating). Apparently some of the aftermarket tstats they were buying were actually hot-side designs, and acted weird in their cold-side application. Given Nissan's 190F tstat was intended for hot-side use, maybe that's part of why the TSB warned about it cancelling a VG's birthday. Of course that thread was about a very different engine, and unfortunately it was more pissing match than thread (maybe they'd just found out about the cars and coffee memes?), so, handful of salt there.

 

On 5/3/2025 at 7:39 AM, adamzan said:

Regardless, the heater barely holds up even in -15C around here.

 

Yeah, mine struggles down there too. It usually kicks in enough to keep the windshield clear by the time I've got the ice off the windows, but sometimes even that seems like a fight. Hopefully the 180 turns that around.
 

Weirdly I've noticed my heater seems to warm around the stereo as much as it warms anything else. I suspect the foam sealing the dash vents together has seen better days. That's probably not helping.

[adamzan]

I remember in college with my old 95, when it got even colder in the winters, it was either see out the window, or have warm feet lol, couldn't have both.

[gamellott]

16 hours ago, adamzan said:

I remember in college with my old 95, when it got even colder in the winters, it was either see out the window, or have warm feet lol, couldn't have both.

I had an 82' 200SX that the heater never seemed to work when it was frigid outside. I didn't have it for too long, so I never figured that one out. Maybe it was a similar cooling structure... Common theme among old Nissans?? 

[Slartibartfast]

18 hours ago, gamellott said:

Common theme among old Nissans?? 

 

I remember reading about an issue with the Japanese starter motors in some '80s or '90s Chrysler? vans. They didn't work in Canadian winter temps, because the grease froze solid, because the engineers had not considered that anyone would attempt to drive a car when it was that cold outside.

 

A similar thing happened with the steering transfer boxes in the early R50s. Nissan had to do a recall (#96V034000) for the grease freezing up in the steering transfer box. The recall said it got so stiff below -30 C that "some drivers would have difficulty turning the wheel."

[adamzan]

I know for me at least, it was just lack of knowledge back then, didn't know you could just put different temp thermostats in.