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:

jcorenman

What was wrong with the 75C Wahler?

captainOCD

Nothing was wrong with it as far as I was concerned. I was going through the checklist of things before installing Ken's S300s chips in my car, and it appeared that an 180f/83c temp stat was what they were intended for. I emailed back and forth a few times with Ken and he says 190f on the water bridge is ideal. You'd think a 180f stat would do this, but at least for me it was running nearly 40 degrees hotter than that in some cases.

DHS928

OK, I have a 94 XJS-V12 and the engine also uses "double action" thermostats, so when open the bypass system is closed off and all the flow goes to the radiator. When the stat closes the by-pass is open and coolant continues to circulate in the engine. Aluminum engine blocks need continuous circulation so no hot spots will form in the system and form steam. Iron blocks are much more resistant to warpage and the old single action stat worked OK. So the jag group was noting issues with different stats also so "yours truly" ordered a 180 from each manufacture that I could identify. Then measured a thermostat housing I got off eBay, I drilled a hole in the side so I could see the bypass plate with the stat seated in the housing. Then tested each brand of stat with it in boiling water, only one brand opened far enough to actually close the bypass completely! The rest left a 2/3mm gap that "short circuited" the system and let hot coolant bypass the radiator, since the suction from the water pump would pull coolant through the bypass since it was closer to the pump. All of us had marginal cooling issues, going to the one brand that had the most piston travel and fully closed the made the difference. All these were NEW stats sold by different Jag suppliers.
So you might try measuring the travel of each stat and even the Wahler and that could be the issue. It drove the jag crowed nuts for years with the V-12's, I would have to go look at JagLovers site to find my post and photos I took at the time.

Dan

captainOCD

I wonder if that could be the case here too. I ordered a new 75c stat (since the one I put back in is from 03) from Roger that should be here in a week or so. I may need to toss it, my current one, and the other two stats in some water and measure how far they open. I think I saw the wsm list a travel spec of 8mm, but I don't think it specified how far from the mounting face.

I won't be able to boil my water bridge, but I'm hoping I can measure the depth of it. Then can compare that to the stats.

DHS928

This is the Gates it opened to 1 3/4 inch and was the only one to completely shut the bypass all this he others were 1 1/2 inch and left a quarter inch opening that allowed hot coolant to stay in the engine.

captainOCD

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.

MFranke

Have you already tried thoroughly burping the system?

captainOCD

Yes, squeezing hoses with front end elevated and running, taking bleed hose off radiator and letting coolant run out, pulling a vacuum from the cap, driving it 1000 miles, etc.

928NOOBIE

I think I'm going this route when I change the thermostat next: https://www.pelicanparts.com/More_In...6&sorter=brand

The Gates branded thermostat for our car is more than the OEM one...LOL....

captainOCD

Yup, that's the wahler 83c one I just took out.

Speedtoys

Measure the distance from the Thermostat seat, to the inner seal...curious..

captainOCD

That was the 33mm I measured on my tan car. I may not have explained what I was talking about well.

Speedtoys

AH yes, sorry, I see it there now.

Speedtoys

Any difference in the width of the bottom plate that seals on the inside?

What are we looking for..a flow difference?