8 cylinder front engine iconic vehicle
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By captainOCD
As part of my intake refresh earlier this spring I put in a new motorad 180f/83c thermostat (drilled a bleed hole in it too) and the bypass seal was already fairly new. The thermostat that was in there was a 170f/75c wahler. The past several years I've had the car (86.5 us) the temp always stayed pretty close to the first white line (marked 170 on some cars). Water bridge temps were normally in the mid to upper 180s as measured with an infrared temp gun. I could sit in traffic on a 90+ degree day and the temp would never go above half on the gauge.

With the motorad 83c stat the gauge was hovering from about half on the gauge to the upper white line. I'd notice it oscillating between half and the upper line (marked 210 on some cars) every minute or so even at steady state 50mph driving. Water bridge temps were hovering around 215f when at the upper white mark. Then one day sitting in a drive through in ~80f weather with the a/c on the temp got about a needles width above the upper white mark. When pulling back out onto the road with moderate throttle the car pinged some, so backed off the throttle. Once moving it cooled back down to just around the upper white mark again.

At this point I wondered if that motorad stat wasn't working well, so I installed a new wahler 83c stat. It hasn't gotten quite as hot as it did when it pinged, but it still is hovering from halfway to the upper mark. Temps on the water bridge around 215-220. I put on a new fan clutch because the old one definitely felt like it had leaked some fluid over the years, but that didn't change anything with the temps. Driving 70mph down the road even the temp was still sitting pretty high.

Today I decided to put the old 75c wahler stat back in to make sure I'm not going crazy here. Sure enough the needle won't quite leave the first white line now. Water bridge temps are sitting in the mid to upper 180s. Even letting it idle in the driveway (mid 90s ambient) with the a/c on the highest water bridge temp I could see was 192. So that tells me that something is up with both the 83c wahler and motorad stats as it seems like the car's cooling system has plenty of capacity to dissipate heat otherwise.

I threw both of the 83c stats in a pot of water on the stove. The motorrad cracks open right at 180f and was fully open around 200f. The wahler waited until 182 or so to crack open and was also fully open right around 200f. I had already put the 75c stat back in the car at this point, so I wasn't able to compare the amount the rear section moved to seal off the bypass.

All I can think is that the 83c stats aren't sealing off the bypass somehow. Again that seal is new and doesn't seem to be a problem with the old 75c wahler. I'd expect to see the water temp running closer to the 200f that the stat is fully opened at then and not getting up to 230. This makes me wonder if that's the problem with my tan 86.5 project car overheating too.

Anyone have any thoughts or notice anything weird with new thermostats lately?

Some pics:

New 83c wahler top, old (dated "09 03") 75c wahler bottom. Didn't get a picture of the back, but the bypass sealing disk looked to be the same size on both.

New 83c wahler left and new 83c motorad right. Both fully open, water temp between 200 and 210f.


Bypass seal:
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By worf
captainOCD wrote: Mon Jul 05, 2021 11:12 pm Anyone have any thoughts or notice anything weird with new thermostats lately?
Short story: installed a MotorRad and had to warranty R&R with a Wahler about 10 hours of operation later. This was about two years ago. My testing told me that the MotorRad opened inconsistently and the opening was smaller when it did open.

iMO, the thermostat should be fully open by 195°F. But, when you’re boiling water on the stove you can’t control the speed of temperature change.

I wonder if you got a counterfeit Wahler?
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By captainOCD
I'd hope it's not fake, it came from Roger. The only thing that seems a bit odd with the wahler looking at it more is that the rear disc that seals to the bypass doesn't look completely parallel with the front disc. It has about 1mm of runout, but I'd guess the spring would take that up.

It just is really strange that it appears to operate properly on the stove, but behaves so odd in the car, especially 2 different thermostats.
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By captainOCD
It was suggested that perhaps the rear disc of the 83c stats weren't opening far enough to seal off the bypass. To test this I put the new wahler and motorad 83c stats in some hot water today.  Also took the old wahler stat out of my tan 86.5 car (not the blue one the rest of this has been about) and checked it.

The procedure here was bringing the stats up to a boil in water, measuring at 210 then measuring the remaining temps as the water cooled slowly.  One thing worth noting is that the wahler stats seem to be much slower to react, both opening and closing than the motorad.  The distance measured is the mating surface of the thermostat where it sits against the water bridge to the mating surface of the rear disc where it seals to the bypass seal.

(again this old wahler is not the 75c stat currently in the blue car)

The tan car also has a new bypass seal.  I measured the distance from it to the edge of the water bridge to be just a touch under 33mm.  So unless the distance is unusually larger in my blue car, you'd think they should be completed sealed off when the stat is fully opened and certainly shouldn't be getting up into the 220s and 230s.
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By worf
captainOCD wrote: Tue Jul 06, 2021 6:55 pm So unless the distance is unusually larger in my blue car, you'd think they should be completed sealed off when the stat is fully opened and certainly shouldn't be getting up into the 220s and 230s.
The most obvious explanation for any thermostat not closing against the inner seal is the outer seal being on the wrong side of the thermostat.

If we assume that there's no measurement noise in your table data, then ...

... the Motorad isn't closing off the bypass until 195 while the wahler closes it at 185.

Take a look at the actual opening diameter and the "throw" of the Motorad versus the Wahler. As above, the Motorad I replaced couldn't flow as much water when fully open as the Wahler (and this Motorad was "sticky" when testing in water.)

At operating temperature on a hot day, cruising at 90 mph, the engine core temperature should be the same with an 83c thermostat as with a 75c thermostat. Either will flow the same volume of water from the radiator once fully open assuming the only difference is the opening temperature.

IIRC you've been chasing this for a while right? Posts in another thread too. I asked about water pump?
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By maddog2020
this is good timing. I have to install my thermostat in the next couple of days. I'll have to see what I have in my box o parts.
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By captainOCD
So the tan 86.5 has been having problems. I haven't resolved that yet. This issue was with my blue car though. It never had temp problems with the 75c wahler. It had problems with both the 83c motorad then 83c wahler, and is back to normal with the 75c wahler.

I was going to work on tracking down if the tan car had decent water flow today, but my 3 year old fuel hoses there decided they identify as a collinder now.
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By Bertrand Daoust
I experienced the exact same situation with my car few years ago.

Back in 2010 (I think), I decided to put a 75d thermostat in my car.
The idea was to lower the engine operating temperature.
I tought back then that this might be a good thing.
(BTW, I don't remember what was the gauge reading temperature with the previous 83d thermostat)

What I remember very well though is that with the new 75d thermostat the gauge needle was always about 1-2 needle above the first white line during normal summer driving.
It even stayed under the first white line during an autumn ride... About -5d C.

I then started to asked myself it this was a good thing to run that cool and asked the question here.
The answers from few members was "No".
I remember reading that the 83d thermostat provides the ideal temperature for the best engine efficiency.
I then decided to go back with a 83d thermostat.

And since this new 83d thermostat is in place, the gauge reading is always reading half a needle below the second white line on the highway and right on the second white line in town.
I mesured few times the temperature at the water bridge with my IR gun and get from 90 to 100d C on the upper hose side (coolant to radiator). Even a bit higher than that on real warm days.
And about 12-14 degree less at the water bridge on the thermostat side (coolant from radiator to water bridge).

220-230d F is a bit higher but not by much.

And BTW, with the 75d thermostat, I believe the car was running richer too...
it's been a while, but quite sure the car was smelling more (burned gas)...
Easy to notice in the garage...

Just wanted to share my experience on this.
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By captainOCD
If the temps would stay closer to the 195-210 range like yours I think if be ok with it, it hitting 230 just has me feeling uncomfortable. Maybe there is something else going on here though.

I did try to double check that my ir temp gun is reading accurately too. Not very scientific, but my Durango has the factory temp sensor on the manifold and a Dakota digital fan controller in the upper hose. With both of those holding right at 195 (as read by obd and fan controller) I measured 195 exactly on the upper hose sender body, and a few degrees lower on the manifold sender. So I don't think the higher temps were a misreading here.

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By Bertrand Daoust

Just to make sure, you're taking the temperature on the water bridge itself.
Not on the hose. Right?

There's a big difference between the two.
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By captainOCD
Yep, I was measuring on the water bridge right at the body of the sender. Seemed to be about the same on the water bridge itself vs on the body of the sender (both the temp II and gauge senders).
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By PorKen
Grrr...mechanic did not change the rear seal on this 89? Or it rusted in 10 years, in good coolant?

Rust marks on t-stat show where rust bubbles have burst. Gaps may be from removal but bumps and hard rubber mean it did not seal well.
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By captainOCD
Yeah, looks less than ideal there. My car has still been happy with the 75c stat. Was gonna change the radiator fan temp switch for one a bit closer to the stat temp, but the one I got arrived incorrect. I'm hoping to put the new 75c stat from Roger in my blue car and see if maybe the old 75c stat going into the tan car might bring it down some too (that car still needs lots of other work anyway).
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