Confused about thermostat for 308QV

I know this has been hashed out before, and believe me I have tried to read what I can... but I'm confused. I have an '85 QV and want to put a fresh thermostat in. The one that came out appears to be original:

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My understanding, from reading the birdman thermostat writeup, is that the plastic "stopper" is important:
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It confuses me, then that Ferrari seems to want to sell a unit without the stopper:

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I also note that many of the aftermarket thermostats that in theory might work have stoppers that are very different than the OEM unit. For example, on the left is one that I bought and am hesitant to use because the stopper is seemingly too small:

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So... is the stopper important? What thermostat should I run? Thanks.

 

It's important, also per the wsm there's an opening rate based on temperature, it's not an open/close thermostat. Correct stat is needed for proper operation.

 

I haven't looked at it but doesn't the Birdman writeup include some info on which aftermarket Tstat he recommends?

FWIW, when I installed a new Tstat in my 328 some years ago, I bought a Stant from the local parts store. Been working fine for years.

 

I put a Beck/Arnley 143-0640 in recently. But I feel like the car does not behave as well as it did before with the OEM thermostat in it. For example, when it warms up, it'll get a bit over 195F and then suddenly drop to 170F or so. I'm assuming that's the thermostat opening suddenly instead of progressively, but I really have no idea. It also seems to be a bit erratic on the road. I don't have hard data so my analysis is more gut feel than anything, of course, but the only thing I've really changed is the thermostat. I'm fairly sure the system is bled correctly.

I'd prefer to put am OEM part in and be sure, even if they are expensive, but I don't understand why Ferrari is trying to sell a part that doesn't appear to be correct.

 

If I was concerned (or the Stant I bought hadn't worked properly), I'd just buy the Tstat from Ricambi. My experience with them over 14 years is that if they are selling a product, it works!

 

I looked there. They have the same "problem":

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If we're saying the -A thermostat is correct, then we're sort of admitting that everything that's been written on the subject is wrong, aren't we?

 

The pictures of the available 308 thermostats at SuperformanceUK look like better equivalent alternatives (about 1/2 way down on the page):

https://www.superformance.co.uk/308/cooling.html

(But don't get that paper gasket shape? Although like the sealing gasketry material on the plunger rather than just a bare metal plate.)

 

Yeah, this one in particular looked interesting to me: Image Unavailable, Please Login

I liked the rubberized looking plunger, seems like it would seal nicely. The original is plastic, which I thought was nice... no chance of wearing the thermostat housing and probably seals better than the metal found on others. And yeah, I didn't understand the gasket shape in that picture, either, but whatever, I have a "real" new gasket.

Probably over thinking this, LOL.

 

I sent Maranello Classic Parts an email last night showing them the issue and asking what thermostat would be correct for me. They responded, "Yes the Thermostat’s can be rather tricky! Infect you require part number 109671/b". Very confusing, indeed.

 

I purchased the one from Superformance listed as OEM a couple of months back and seems to work perfectly


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The one you removed is correct, I would put it back in!

Once they overheat you need a new one. After my last one went bad, no one could match the "plunger design" so I went to Ferrari of Houston.

The housing gasket, the correct unit, and the sealing ring (NOT an O-ring it more of a channel shape, around the metal plate) were about $300.
I have since sourced the proper unit from Italy, it was about $30.

 

There a list of T stat in the first page of the 308/328 Cross Reference section. It does say “not OEM” but the question is does it work? https://www.ferrarichat.com/forum/threads/308-328-gtb-gts-dino-gt4-parts-cross-ref-thread.64460/

 

Yep!

The only thing that matters is that the thermostat works properly, not that it looks exactly like the no-longer-produced OEM thermostat. The Stant in my 328 does NOT look like the OEM Tstat but has worked perfectly for over 10 years.

 

I've been thinking this may be the move! After testing it in some hot/boiling water to make sure it operates correctly. I don't think there was any reason to believe it wasn't working before I took it out, I just replaced it "on principle"...

 

Obviously, I agree... but in this case, "looks like" actually matters because the physical design is an important part of operation, ie the plunger needs to actually act as a stopper. I wish I had hard, recorded data, but my car pre-thermostat change would run just under 195F, and that was during 95F days during the summer. After pulling the OEM themostat, it tends to run 195F or just a tick over it. I'm postulating that the stopper design of the unit I put in isn't right. Probably wrong, of course, LOL.

 

Tested my old thermostat. It seems to work fine. And my tea kettle makes very accurately heated water, too. I guess I'll just swap it back in and see what happens. Sorry for noise.

 

If you look at how the Tstat functions, whether it seals "perfectly" or not is does not make any real difference. The amount of "leakage" that could occur in the closed side is so slight in comparison to the amount of water being moved through the open side that it has no actual effect on the cooling system capacity. I suspect that it why the OEM-type Tstat isn't made anymore...it's not necessary. It might be "better" from a theoretical standpoint but from an operational standpoint, it has no benefit.

 

That's not accurate. I'm not really looking to get into an argument over this, so feel free to ignore it or draw whatever conclusion you wish. I get your view that in simplistic terms the std single plate stat works so no need to bother with the fancy dual one. Unfortunately, that is completely counter to the design and engineering of the coolant system flow.
The pressure head is on the back side of the lower plate, that forces it to close against the upper chamber. It's a dual function stat, upper plate flows to radiator, lower plate regulates the exchange rate to the block from the heads. Reduces thermal shock or big swings in temps. Stable temperature is the goal and that's what the funny dual plate stat is doing.
By using a single plate stat the cylinder head flow will dump right back into the block, temps rise faster in the block, swings are very apparent on the gauge and the block will ultimately run a touch warmer, but more importantly it'll not run a stable temperature.
Just my 2 pennies...

Yrs ago we ran that test on a test engine, both on the Dyno and in the vehicle. Temp swings were too great and it ran up to temp very quickly. We had the engine monitored via temp probes in block, cylinder head and radiator monitored by the ECU. At the time we couldn't source a correct stat, so ran a single plate and tested it, once we tracked down the correct one we tested that. Conclusion... Run the dual stat. Ferrari engineers knew what they were doing.

 

That's awesome. You describe exactly the kind of behavior I feel like I'm seeing on the gauge. Of course, it would be much better to log it and prove it with hard data, but... anyhow, will put the OEM thermostat back in and I'd bet it returns to normal.

 

They DO "still make it, as I posted, I have purchased two of them in the past year.

The second one is sitting "somewhere" in my tool box.....
Now I DO readily agree that even places like BAP/Geon that should have recognized it, were stumped.....

 

"That's not accurate. I'm not really looking to get into an argument over this, so feel free to ignore it or draw whatever conclusion you wish. I get your view that in simplistic terms the std single plate stat works so no need to bother with the fancy dual one."

Sorry if I was unclear. My point was that the rubber or plastic seal that the OEM Tstat has is not necessary. That's the only point I was trying to make. OTOH, as you noted, the single plate Stant on my 328 works perfectly though that may have as much to do with the superior cooling system of the 328. It may be that the 308 is critical re that Tstat and the 328 is (obviously) not. I say "obviously" because my 328 has been tracked at 145+MPH and sat in 108F degree heat in bumper to bumper traffic with no overheating issue at all with the eight dollar Stant Tstat.

 

Thats a little misleading to say that the "rubber seal" is not necessary. IMHO it is, but a critical point on the thermostat design and selection is the primary disc travel. If you can get a new thermostat, including all other specs such as temp, secondary and primary disc diameter etc, that has a (metal) primary disc travel equal to the OE (rubber) disc then you will OK although I would only ever select a unit that has the rubber disc.

Temperature fluctuations are caused by the use of a metal to metal seal on the bypass chamber, it does need the rubber washer / disc!

NB - The rubber seal is on a metal disc to prevent it collapsing, you need to stop any short circuit through this chamber when up to full working temp and pressure.

Best

Tony

 

Without comment (because none is required) take your pick.

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There you go, looks like plenty of choices! I also did some searching and the "dual action" thermostat is readily available from a variety of sources. However, if you insist on the plastic/rubber OEM-type seal on the bottom section, that seems difficult to find. In that case, I would plop the OEM in a pot of water and check its function. If it works properly, put it back in the engine and let it continue to function for the next 30-40 years!

 

Please tell me you are joking!