Intake Manifold Thermostat - How do I check it and service it?

[Zup]

Damn---wish it had turned out differently Namerow!

A quick google search turned up this:

 

http://forums.hybridz.org/topic/109345-su-carb-manifold-heat-control/

An interesting discussion of this occurred in 2012 between TonyD (knower of all things) and JimCan over on Hybridz.

Seems there is/was a replacement out there (but as always not cheap)

Here's the .pdf of the unit-------

Manifold water control thermostat TVHAT.pdf

Unfortunately Therm-Omega-Tech does not seem to exist anymore. All searches for links to their homepages and such that I have done appear but "Page cannot be displayed".

Maybe they've been bought out and there has been a name change or something---I dunno.

I'll do some searching at McMaster-Carr. They have a lot of industrial application stuff that may turn up something useful.

 

 

 

 

[Namerow]

Hah!  Gentlemen, we have closure!    My manifold heat thermostat now performs perfectly.  Here's what I did (after the four-hour soak in C-L-R, of course):

The little adjustment screw and locknut that appeared to be seized together forever were, in fact, soldered together.  If you look closely at my #3 photo above, you'll see what appears to be a shiny-silver, crowned nut.  It was only when I put my micro-torch to it and saw things starting to melt that I realized the truth. 

• I broke the nut free from the (brass/copper) top plate first using a 4mm box-end wrench and then backed it off about one full turn.  Then I tackled breaking the adjustment screw free from the lock nut.
   
• I rigged things up in my bench wise so that both thermostat housing and box-end wrench were anchored and could turn and so that the wrench couldn't lift off the nut when I tried to turn the screw (sorry, no pix -- not enough hands).  That left one hand free for the torch and the other for the screwdriver.
   
• You need to find a screwdriver whose blade fits tightly in the slot on the end of the adjustment screw.  Otherwise, you'll round out the slot and it'll be 'game over'.
   
• Heat with the torch until the solder melts enough for the screw to turn within the nut.  Then turn the screw in until you use up the available adjustment.
   
• Now, put the torch way and turn the re-locked screw-and-nut with the box-end wrench until the nut snugs up against the housing's top plate.
   
• With a small-dia. pin punch, push Item #6 ('Supporting Plate') down against its spring a few times, just to make sure it's moving freely.
   
• Now test in a big pot of boiling water, using the test method mapped out in the FSM (see Zed Head's posting, above).  Do NOT accidentally suck boiling water up the hose into your mouth!
   
• Assuming that your 'hot' test is successful, now dunk the assembly in cold water and verify that the valve re-opens.
   
• Re-solder the screw/locknut pait to each other and to the housing's top plate.
   
• Have a beer to celebrate your now-ready-for-action, 40-year-old, NLA-anywhere, 'Manifold Heating Thermostat / Switch' !

p.s. I am now taking orders in my new retirement business of fixing Nissan manifold heat control valves.  May I take your order, please?

WARNING:  This is a fiddly little job.  If you lack patience or have had a couple of beers to get prepared, you will likely end up with: 1) a broken valve, 2) burned fingers, 3) scald marks, 4) all of these.

Also:  Don't forget to do the boiling water test before you start.  No point wasting time on a job that doesn't need doing.

[Namerow]

Re Zup's last post:

Thanks for the link to the HybridZ posting.  The possibility of water pump cavitation might support my fears that this silly little valve is more important than it may seem at first glance.  Not sure if the cavitation issue has ever been verified in actual practice, but it seems plausible.  Anyway, I hope that my discoveries over the last 24 hours will provide a new option for Z owners who don't have their valve installed but still have it tucked away in their spares bin.  Maybe zCars will have his two about-to-be-restored manifold thermostats up for sale on eBay soon! 

 

Edited January 10, 2016 by Namerow

[CanTechZ]

 Lot's of good info here, thanks for sharing this. 

Was the manifold thermostat first installed on the 1972 model year as that's what it seems to state on page EC-12 of the 1972 FSM.  I don't have one on my 1970, and I don't believe there ever was one, also I can't find any mention of it in the 1970 FSM.  I see the benefit of having this thermostat, I'm just curious about when it was introduced.

[zKars]

Alrighty. Found my stash of these valves.

Discovered there two slightly different ones, the cap on two are aluminum, the others are steel. All bodies are all aluminum. I took the cap off one of the aluminum ones, the threads didn't survive. Took one steel cap off, no problems. Clean threads. All my valves are plugged with deposits, but they disolve quickly with Muratic Acid. CLR is slow for sure.

Since the aluminum capped one is toast, I attempt to extract the guts. Success! Came right out. I used a set of bent nose c-clipp pliers as a pin wrench. Just twist until it gives. Now I can clean and rebuild the interior bits.

Can't see why most of these wouldn't be restorable as long as body threads are good and the inside bits are badly corroded.

One more observation. The fluid sealing cone is metal, likely brass. It seals against a tapered section of the body. No way this would ever made a perfect seal. Note the FSM statement above in the test proceedure about "little or no bubbles". Makes sense now. 

 

Edited January 10, 2016 by zKars

[Namerow]

Great photo, zCars.  Now we have a full understanding of what lurks inside the little cylinder.  Not sure if I'd be willing to try that if I only had one thermostat at my disposal.

Some further thoughts, and then I'm going to return to my plating project .

1. I did not, unfortunately, use the 'scientific method' when I was fooling around with my thermostat this morning, so I can't really say for certain that re-setting the adjustment screw was what solved the problem.  Other possibilities:

• The heat from my butane torch might have 'excited' the wax in the actuator pellet much more than dousing it in boiling water, to the extent that expanded with enough force to break the output shaft (the one with the 'foot valve' and e-clip on the end) free of whatever crud was making it bind.  All I can say is that the main housing was too hot to hold after I got done with my de-soldering exercise.
   
• Tapping on the end of that shaft with my pin punch might have also contributed to breaking it free.
   
• There may never have been a problem with my thermostat in the first place.  Yesterday, I had it immersed in only about 2 cups of boiling water.  That may not have been a big enough heat sink.  Today, I switched to a big pot of boiling water on top of the stove.  The valve was closed tight in about 30 seconds or so.
   
• Steel cap on aluminum housing.  That sounds like a recipe for disaster in a cooling system component.  My unit is aluminum cap / aluminum casing.
   
• To CanTechZ's point, I'm not so sure that it wasn't on the Series 1.  The wording in the 72 FSM is a little cryptic, in my opinion.  Also, the Parts Manual doesn't show any start date for this part -- just an end date.  That implies that the manifold thermostat was part of the design from the get-go.  Given that the thermostat operates in 'closed' condition under normal engine operating temps, its absence in this secondary coolant path would lead to manifold heating under hot engine temps.  That seems wrong.  The no-thermostat solution to this would be to block off the circuit -- which would beg the question of why the circuit is there in the first place.  Do you see it otherwise?  Maybe Carl Beck or 27th can comment.

2.  It occurs to me that the thermostat's adjustment screw may not be so much for ensuring that the valve closes fully, but rather, how much time it takes for the valve to close.  Of course, it may affect both.  zCars' new photo shows about 3/16" of exposed thread on the stem of the adjustment screw.  Mine started off with about 1/8" of exposed thread, so comparable.  My car was made for the USA/Canada market and I suspect zCar's was too.  More exposed thread on the adjustment screw implies longer travel (valve starts off further away from its seat), thus longer time before the valve meets the seat.  Makes sense for moderate-to-cold climates.  I wonder if Nissan dealerships in tropical climates got a field service bulletin suggesting that they trim the valve for less travel/faster close?  (jalex, are you listening?).  If so, I've now got mine adjusted for 'tropical' conditions.  Maybe I need to try the boiling water test again, with the screw set back to where it was in the first place! ...

(pause)

Yep.  Confirmed.  I went back to the shop and backed the screw out about an 1/8" and then put the torch on it like previously to get things 'warm'.  Valve closes nicely.

Conclusion:  It now looks like the the C-L-R dip followed by the combination of thermal shock (torch) and impact (hammer and punch) is what did the trick.  Turning the adjustment screw in and out might have helped, but I can't say for sure. 

I'm leaving my adjustment screw back at the 'factory' setting.  I'll put a single wrap of teflon pipe-thread tape on the housing/cap threads, tighten things down, and then declare it, 'Job done'.

Small part.  Long story!

 

[CanTechZ]

19 hours ago, Namerow said:

 

• To CanTechZ's point, I'm not so sure that it wasn't on the Series 1.  The wording in the 72 FSM is a little cryptic, in my opinion.  Also, the Parts Manual doesn't show any start date for this part -- just an end date.  That implies that the manifold thermostat was part of the design from the get-go.  Given that the thermostat operates in 'closed' condition under normal engine operating temps, its absence in this secondary coolant path would lead to manifold heating under hot engine temps.  That seems wrong.  The no-thermostat solution to this would be to block off the circuit -- which would beg the question of why the circuit is there in the first place.  Do you see it otherwise?  Maybe Carl Beck or 27th can comment.

 

 

I can't be certain that my '70 car never had this part, but I have owned it since 1978 and I did not remove it.  To me it seems strange that the manifold heat control thermostat is not mentioned in the 1970 FSM. Also in looking at the parts manual I noticed the pipe manifold that wraps around the back of the engine connected to the hose that connects to the thermostat did change in 09/71 (item 26 on the attached parts book page). On my car the thermostat would not physically fit unless I bent or modified that pipe manifold. I could be wrong but I think the fact that there was no start date in the parts book for the thermostat might indicate it could be backwards compatible if you also change to the newer pipe manifold (p/n 14053-E8800).  Just some food for thought.

Mike

Edit> I missed answering your question about "no-thermostat solution and blocking off the circuit etc." Your logic does seem to make sense, all I can add is that over 38 years of driving my car and not having this thermostat with the coolant path open I have not had any issues.  Maybe others with original series one cars will jump in and offer opinions or confirm if this part was in fact originally included on their car. I wonder if anyone has an old parts book from 1970, mine is from 1978.  To me it looks a little ambiguous that the item 38 thermostat is offset and parallel to the pipe string and why would item 20 (connector-water) be required when the thermostat case cover can thread directly into the intake manifold? Just curious.

Edited January 11, 2016 by CanTechZ

[Captain Obvious]

I don't have anything technical to add to this discussion, but wanted to say that I really enjoy the investigative work.

[Zed Head]

Interesting also to note that Nissan put so much effort, including a page and a half in the FSM, in to a tiny device that hardly anybody knows about.  It must be solving some problem.  Automakers are notoriously cheap.

[Stanley]

Good investigation, guys. I'm also puzzled about the "direction of flow" issue. Since the water pump normally sends coolant through the engine, thermostat, radiator, and back through the water inlet, I thought with the thermostat closed the coolant would go through the manifold, manifold heat control thermostat, and around to the water inlet, in that order. Where does the coolant come from if it's going the other way? Seems like position of heater valve might have something to do with it, if the heater's in the loop.

Regarding the cavitation issue, seem to remember seeing a little metal tube going around the front of the engine, connecting to a barb on the water inlet, on 280 Z's. Don't think there's a hot=closed thermostat in that line, but wondering if it's to reduce cavitation when the thermostat's closed.

I planned an experiment  (after reading the HybridZ thread a couple years ago) running a clear line from the outlet on the rear of the head to the lower outlet (OK, inlet) on the thermostat, just to see which way it flowed, but the "clear" high pressure silicon tube that I ordered wasn't clear enough to see flow direction, so I abandoned it.

Perhaps a beer will clear my thinking....

[Zed Head]

I saw Namerow's comment on flow direction but didn't ponder it deeply.  If direction was determined form the test procedure , maybe that's where the question develops.  Direction for testing probably wouldn't matter.  The flow diagram shows flow from the housing, through the manifolds, and to the water pump outlet.

[Namerow]

@ Zed Head and Stanley...

You're right, I'm wrong.  I was tricked by a my too-quick look at a different coolant diagram that appears right at the beginning of the '72 FSM's Cooling System section (see Fig. CO-1, below).  While re-visiting my notes, I found a nice flow diagram (copyright credit to Bill Wilhelm) that Blue posted some time ago - also re-posted below.  It provides some additional insights.  All in all, though, Fig. EC-23, is certainly the definitive one when it comes to figuring out how the Manifold Heating circuit works.  Specifically, until the main (rad) thermostat opens, the Manifold warming circuit is active.  Coolant enters and exits the main thermostat through the base of the main thermostat's housing.  Intersting that Fig. EC-23 was included in the Emission Control section rather than the Cooling or Fuel sections.  Maybe the tech writers at Nissan just treated the Emission Controls section of the FSM as the dumping ground for, 'little gizmos that nobody understands'.

I think the point still stands that if the Manifold Thermostat is stuck open (or removed), then the manifolds and carbs are going to be seeing some degree of heating even after the engine has reached normal operating temperature.  That is, unless pressure differentials change when the main (rad) thermostat opens, so that the flow through the manifold heating circuit is reduced or stopped.  The only way to tell would be try a different version of Stanley's aborted experiment by replacing the rear transfer pipe with some kind of clear tubing.

@ CanTechZ...

I have two rear transfer pipes (Item #26 in the parts diagram).  One is known to be from my old, one-owner '72 Z.  The other I recently pulled off my current '70 Z.  They're identical (although the '70 has gone through several hands, so I can't guarantee that all the parts are original).  I take your point, though, about how the diagram implies that the Manifold Thermostat (Item 38) is a substitute for a plain Connector (Item 20).  I wonder if the early design for the manifold heating circuit tried to get by without using a thermostat (see my comments re system pressure differential, above), only to experience some kind of unforeseen problems that made it necessary to add the t-stat ($).  I certainly agree with the comment that auto manufacturers resist adding anything that they can't charge premium money for... like, say, racing stripes, alloy wheels, sunroofs, chrome side trim strips, rear hatch louvres, etc. Oh, sorry -- it was the dealers who added those, wasn't it.