MFI thermostat spacers

[Grady Clay]

John,
I thought of a couple more things.

With the thermostat housing empty, bolt it to the pump with the gasket and shim in place. Use the support shaft, with snap ring in place, to actuate the little thermostat lever in the pump. You want to insure it has smooth operation until it hits the stop. Note that there is clearance from the snap ring to the housing.

When you have the thermostat reassembled, a useful thing might be to measure the position of the shaft at various temperatures. I would choose ambient room temperature, in the oven at say 150-175F, and in the freezer at 0-5F. You will need to let the temperature stabilize for a while and record the actual temperatures. I think your vernier caliper should be sufficient for the measurements. Just hold the thermostat where the shaft is up and don’t load it with the calipers.
Perhaps some other Pelicans will measure theirs also.


Ed,
The problem of oil dilution with gasoline is almost always caused by the thermostat set too rich and/or not turning off soon enough. Yes, too rich main mixture can cause it also. A cold 911 MFI will run just fine (actually great) when it is really rich. Some of that excess fuel goes past the rings and dilutes the oil.

The technical causes of the thermostat being set too rich are what John is trying to address.
The thermostat not turning off soon enough can be from; oil & dirt in the thermostat, blocked air flow from the heat exchanger (mice, tubes coming apart internally), air leakage (torn tubes, rusted out heat exchanger), and the relationship of number of bi-metal discs, shims, etc.

The worst case oil dilution is from a MFI engine being repeatedly started, driven, and never warmed up – particularly in cold weather. The dutiful shop that starts your car and brings it inside every night and puts it out in the morning can be the worst offender.

The usual symptoms are the car appears to not be using any oil or seems to be gaining oil.

If left unfixed, the residual gasoline replaces the engine oil. The engine is constantly using the mixture. The mixture gets thinner and thinner and can become almost all gasoline. One stint on the freeway at operating temperature will evaporate all the gasoline, leaving no lubricant for the engine.
I have seen too many engines blown up from this situation.

Best,
Grady

[donk]

Wow, never thought it could get that bad. I was wondering, is there a way to test if gas is getting into the oil. I assume if my oil is diluted with gas, I would be able to smell it through the oil filler, but is there a more scientific way to test/measure this?

[Grady Clay]

John,
I don’t think it is possible to keep all gasoline out of the oil. The key is to get the engine to operating temperature as soon as possible EVERY time it is started. MFI race engines never have this problem.

I use the “sniff test,” if it smells like gasoline there is possible oil dilution. I don’t know if there is a cheep and easy test. Sending oil samples to a lab regularly is an option, abet an expensive one.
I change oil a lot.

The other side of the coin is the issues you are addressing: Having the thermostat provide just enough enrichment to run cold (lean worst running) and to get it to turn off ASAP.

In an earlier thread several Pelicans discussed the condition where the cold start solenoid valve (on top of the fuel filter console) leaks. When I edit, I’ll add that to the CMA additions above.

Best,
Grady

[donk]

Grady,
I've read the concerns about the cold start system. Because of this, I have mine disconnected. Don't really need it in Texas. At this point, I have been considering ditching the thermostat in favor of a block off plate and set screw. I've read all the threads I can find about this topic. I seem to recall seeing that you have done this before. Could you explain the pros and cons of this modification to me?

Thanks

[ed martin]

Hi John, I would concentrate on finding out just how many discs the original designers put in there. All those shims just does't seem right to me. I would go as far as locating another one. You have a long way to go as far as making that engine run right, such as setting the correlation, checking the vacumm advance and the vacumm ports in the throttle housing(make sure they're not occluded as the system typically runs rich and the ports get choked with carbon), adjusting the stacks, and adjusting the part load and idle as per Check, Measure Adjust. Of course it goes wilthout saying that you follow the order and proceedure of Check, Measure Adjust which really translates into checking the fundamental easy things first. Hope you've been doing that because as far as this setup goes, that is your bible. Furthermore I trust you're not attributing the stack popping only to your thermostat. Your thermostat is very important but is only a part of the full picture. You need to go through each componant of the system and get it right and in the order of the manual or you are going to be going back and forth and you're going to experience a lot of frustration.

[Grady Clay]

John,

The pros:
It is a simple device of “local manufacture.”
With proper use it prevents severe oil dilution.
In TX you may not have to use it much.


The cons:
To use it you have to get your tools, open the deck lid, set it, start the car, warm the engine so it will continue to run, and turn it off again. PITA when you are taking a client out and are in a 3-piece suit.
It isn’t OE.
If used improperly you can have outrageous dilution (like you forget to reset it to off.)

One risk is you will be tempted to set the main mixture slightly richer than you would otherwise. Again the compromise; to have it start and run at all vs. run rich.

This “mechanical thermostat” is a good part to have, if for nothing other than as a diagnostic tool.

A properly operating Factory thermostat will work just fine. Like everything in the world; “The devil is in the details.”


I have a 2.8S engine where the MFI pump has the ’69-’71 cold start enrichment solenoid on the pump. It forces the rack full rich. A slight operation of it while cranking allows the engine to start. If it won’t keep running, another slight operation works. This works well in the temperature range where I really don’t need to operate the mechanical thermostat. When it was in cars with heat exchangers, I used the regular thermostat.
If you ever send your pump in for service, that enrichment solenoid is worthwhile.

Best,
Grady

[ed martin]

Hey Y'all, I know from my own experience that there is no need to modify these systems, such as disconnecting the cold start, adding subtracting washers/dics stc. I got my engine running beautifully with all elements as they were designed. I think I was lucky though because I suspect my engine didn't have a lot of miles for a thirty year old car. As for as gas in the oil, my feeling is that this condition is from a tired pump, I really don't think it matters where it's positioned on the rack. Of course this is only my opinion. As far as driving an MFI system and reaching operating temperature, I believe this has more to do with overly rich exhaust and the resultant carbon deposits. Furthermore, the thermostat is simply not an on/off function. It is a gradual expansion from the starting point (rich) to gradually leaning as the temperature increases. As it expands, it provides a constant force on the lever in the space cam housing until it reaches its final limit (lean position). It is at this point (operating temperature) that you want to set the position of the rack (part load setting ) which is responsible for your final rich/lean mix at normal running temperatures. The thermostat is actually a pretty simple design and a very elegant solution to the problem of adjusting the fuel required thoughout the range of temperatures.

[donk]

Ed, I agree with you. My goal is to get the system running right with all its original parts intact. I disconnected the cold start system because I haven't had a chance to test it for proper operation. When I have verified that it is working properly, I plan on reinstalling it, even though it is not really necessary in my neck of the woods. Like Grady said, a "mechanical thermostat" would be nice to have as a diagnostic tool.

Though many interesting topics have been brought up on this thread, my main reason for starting it was to find out the number of spacers that should be in the t-stat. I think we have established that it should be 2, but in the meantime we have wondered how many thermal discs should be in there, and precisely how thick the (thick and thin) spacers should be. If anyone has their themostat removed at this time (or has an extra one), could you please count the discs and measure the spacers for me?

Thanks

[T with MFI]

John

I took a look at my mine (72 T). It has 24.5 sets of expansion rings and 1 spacer. The spacer appears to be the thick one as shown in the original diagram in this thread. I've had the car for about a year. I'll assume that the PO removed the thin ring and possibly one of the expansion rings ??.

The one spacer thickness appears to be the same (or very slightly thicker) than the metal used on the expansion rings.


John G.

[donk]

Hey, first post! Welcome aboard! And thanks for the info.
Anyone else? I'm getting the sense that theere should be 25 sets of thermal discs. Can anyone confirm or deny this?

[David E. Clark]

According to this thread, there are "25 pairs of expansion elements." There is other good information here as well. Hope this helps. This is a great thread.

MFI thermostat questions

[donk]

David,
Thanks, I have seen this thread. Guess I overlooked john_cramer's post that details the number of discs. However, looking at this post, I noticed that it states that there should be three spacers (it refers to them as flat washers). What gives? I thought we had already established that there were only two spacers! Maybe we're splitting hairs here.

[ed martin]

Yeah right, In the Pelican Tech Articles there's a ton of great information regarding many aspects of the MFI setup with one specifically devoted to the thermostat. I remember a few years back refering to those articles. As Dave pointed out, and if you refer to this article, there are 25 pairs of discs and according to the article, three washers. It's been a couple of years, but I still seem to recall one large and one small in the two thermostats that I had. But I would sooner trust the veracity of the text in that article than that of my memory.

[David E. Clark]

I don't know if you are splitting hairs. In my car, 1973 911E, I have two thin spacers following the spring retainer then a thick spacer followed by the series of 25 thermal disks. I posted last year

MFI Thermostat Clarification

wondering if this "extra" spacer was supposed to be there or was placed there by a previous owner in an attempt to lean out to pump when hot. No-one seemed to know if the "extra" spacer not shown in the diagram was supposed to be there or exactly what effect it would have on the warm up characteristics or the "richnness" of the mixture. Since then I've removed the "extra" spacer with no noticable effect; i.e, still rich. I have since put the spacer back (two thin then a thick) and I'm just learning to live with cleaning the plugs regularly! Even though it's rich, the car runs great as long as I keep the plugs and the air filter clean. From everything I've read, and experienced with my car, I am convinced that most MFI cars run better when a little rich. I should point out that I do not drive the car in the winter so I have no experience warming up a VERY cold car. Maybe someone else will chime in

[Grady Clay]

John,
Sorry, the Docs had me all this morning and I’m a little goofy.

When you reinstalled the clean thermostat with all the spacers it probably now was too lean and perhaps got leaner faster – hence the popping (…maybe).
When you took the spacers out that richened the thermostat and probably delayed its turning off. Rich = better running (but not desirable.)

I suggest you try it again with all the shims, put up with the poor running (popping) during warm up, and report back. You want to start off in the mornings as you would normally. You want to correlate the running (good & bad) to the time of running and the engine temperature. Keep track of the environmental temperatures, etc. Do this over several days.

You keep perking my memory. Most amateurs tinkering with the thermostat remove one or more bi-metal discs because they don’t have any extra to add. That makes the system go rich more and not turn off as soon. Of course it quits surging (popping) and all is well – NOT so. It is too rich.
I recall regularly adding a single bi-metal disc to have this configuration; ()()() … ()()()(, where the open disc was toward the shim and spring. It was probably 25 ½ pairs = 51 bi-metal discs.

Hopefully when you disconnected the cold start, you also pulled the wire connection to the top of the cold start solenoid as well as the plumbing.
It is a worthwhile test to go back and add the cold start after you have experienced the just-using-thermostat operation a few times.
Remember, with a properly set thermostat, the engine may not start cold without the cold start enrichment while cranking.

Now is the time to collect all the stuff and other’s expertise to light into the CMA procedure. I encourage you to outfit yourself with all the necessary equipment. This is not a “one time deal.”

So, what do you have?
You have an exhaust gas analyzer on order.
Do you have good compression and cylinder leak testers?
Fuel pressure gauge and method to test flow?
Good, powered timing light?
Cam timing and valve adjustment?
More!
There are lots of tools available from our host, still some P-tools from Porsche, and many from industry. Some you will have to make yourself.

The bottom line is that you want to be able to perform all the diagnostic and service on your car yourself. If not, find a willing mechanic and educate him/her. I would not be afraid of giving or loaning them to the right person.

There are three reasons to own a MFI 911:
- It is the highest performing early 911.
- It has the best throttle response of any 911.
- It is fun (and occasionally necessary) to tinker with.

There is a lot of satisfaction in owning a MFI 911 that you can keep working properly. John, you clearly have the inclination and intellect.
If someone wants a FI system that runs OK but doesn’t perform, try one of the later systems.


Ed,
I agree; we can have our MFI systems (almost) as delivered from the Factory. I prefer using the complete factory system as designed, with some exceptions based on experience.

I disagree; yes we are “…second guess[ing] the engineers at Porsche.” We have the advantage of experience and hindsight. What do you think they would have changed with our current knowledge of chain tensioners, “simplified differentials”, Hydropneumatic struts, rubber center clutch discs, CIS air boxes, etc? MFI is no different.


David,
You are probably experiencing the same thing as John. Your system is too rich. If you can remove a spacer from the thermostat with no effect, you are too rich and definitely not set correctly. Having to clean your air filter tells me you are venting lots of unburned fuel to the air filter. Of course the plugs are also a major indicator.
Please go back and re-read this thread and research others.
You can get your MFI working properly also. MFI 911s perform best just shy of too lean (great) - they run best too rich (not desirable). We will be glad to help.


All:
Please post MFI links (including not Pelican), add your knowledge, or just 2c,

Best,
Grady

[donk]

Grady,
You don't seem goofy to me! I'm glad you recovered from that. Your knowledge on this subject is invaluable.

Just curious, does the order of the spacers matter? I mean, they are spacers, so their job is just to create more space, right? Or is my logic flawed?

I tested the cold start system last night, and it seems to be working correctly, so I reinstalled it. I had just heard stories about the valve sticking open and dumping fuel even after the engine was started. So I disconnected it until I had a chance to test it.

I have many of the tools you have listed, and the ones I hope to find soon. There are a few Porsche specific shops in my area. Not sure if they do much work on MFI, but do you think they might have the Bosch injector tester you mentioned earlier? Is this tester only for MFI? Are these testers still available, how much are they, where can you get them?

Come to think of it, it might be valuable for someone to make a list of necessary tools and diagnostic equipment for the MFI DIY'er. This system can be pretty intimidating for the uninitiated. The more guesswork that can be taken out of the equation, the better.

Another thing I am curious about... Is it more desireable to remove the additional shims and adjust the mixture to compensate, os leave the shims alone and adjust the mixture. I know there are things to check before I even get to mixture adjustments, but assuming I get to that point, what would you recommend?

Surely more questions will follow. There is alot of great info in this thread already, and it is greatly appreciated. hopefully it continues to grow.

[Grady Clay]

John,
Yes, spacers are just that – spacers.

Good that the cold start is working OK. This means you can lean the cold running thermostat and still start the engine.


The range of tools is almost infinite. It starts with the every day tools necessary for any 911 engine and at the other extreme are the tools that the MFI pump builders have. Of course the manufacturers are even more extreme.
The important question is what does the MFI DIY absolutely need and what is just fun. Above some point all of us need to tap the expertise of the pump builders and perhaps the factories.
I think the starting point might be to list all the Factory tools, the necessary commercial tools, the tools “of local manufacture”, and more.

This deserves its own thread.


John, your question about combining or separating the cold running function from/with the main running system is a good one. I think that at first they should be addressed separately. Get the thermostat cold running working predictably, abet “lean worst running.” Get the main normal running (part throttle) working properly with the thermostat off. Make sure full throttle mixture is correct. Get the idle right. Finally, adjust each to have proper transition from one to the other.
Remember, it is easy to adjust everything slightly rich and have the engine run well. For best performance the engine needs to be as lean is possible consistent with acceptable operation.
Of course there are all the precursors; compression, cams, pump timing, nozzle condition, etc.


To answer your question:
“Is it more desirable to remove the additional shims and adjust the mixture to compensate, or leave the shims alone and adjust the mixture.”
It is a sequential, back-and-forth solution. Get the thermostat to turn off soon and not ever be too rich. With the thermostat off, adjust the main (part throttle) mixture for lean best running. Get the idle mixture set correctly.
You will have to go through this loop several (many) times to get the system close to right. It will never be perfect given that it is 30+ years old and wasn’t absolutely perfect to begin with.

Get ready for CMA.

Best,
Grady

[ed martin]

I really believe that the spacers are there to keep the proper tension on the discs so they can perform their function. I would just put in the 25 discs and spacer and washers in place and be done with it. Once you get past that, assuming everything else is together I would set the part load adjustment. To do that I would take it to somebody with a dynometer because the adjustment has to be done while the engine is under load. I tried for ever to do the adjustment myself and could never get it right. I finally went to a mechanic who used to work for Vlasak Polak he used a dynometer to get the CO at 4.5 %. Pretty good! Talk about rich, I had been running it at 16%! I ended up enriching it afterwards just a few clicks because when cold the car would tend to buck. To lean! After that though I was extremely pleased with the running condition of the car.

[Matt Smith]

Ed- you're right, but in a simplistic way IMO. The CMA demandments are fine if you have a brand new 30 year old 911, but the situation gets muddied when you add time, wear and P.O's tinkering into the mix.

I would take all of Grady's advice and run with it as fast as I could. That guy knows his stuff. I know this because he completely answers all the 'Graduate' MFI questions I have been pondering for a few years over- without me ever having to post a question

[David E. Clark]

There is a lot of great information here. Thanks! Grady, at the risk of hijacking this thread, I'm wondering why you keep saying that running rich is not desirable? Is it the obvious reasons, fouled plugs, unburned fuel clogging the air filter, excess fuel leaking past the rings into the oil and lousy gas mileage? My car does run rich (black soot on the plugs and it smells rich) but I don't seem to be getting any gas in the oil (I change the oil and filter every 3,000 miles) and I don't ever let the air filter get dirty. (I have a K&N which I clean regurarly). Finally, since I drive the car almost exclusively on weekends, gas mileage is not that big a deal for me. So my question is, am I doing harm to the car by not leaning it out a bit? I've gone through CMA step by step and have adjusted to lean out the mixture but to me my car always seems to run better a little rich. If you've got time, I'd love to hear your thoughts on this. Thanks,