MFI thermostat understanding/question

[BartdeBruijn]

Hi,

My Thermostat of a 2.2E MFI pump seems not to work (after heating the rod sticking out has exact the same length as when cold... After cleaning the discs (keeping the sequence!) same behaviour, meaning no movement of the rod after heating.

After going through a lot of threads and also the special MFI thread I still don't understand a part of it. Heat makes metal to expand and all the rings on the axes will lengthen, so far so good.
How will this expansion force-wise acts on the rod???
In my opinion the expansion discs will push the little snapring(front of the rod to the housing. On the other side it will compress the spring. but no movement of the pin.....(see pictures)

Hope some ne can educate me here.....

regards,
Bart

[Neven911]

Think of the spring in the thermostat end as a relief spring, so when the disc are fully expanded (which they do by dishing) they have 'overflow' against the end spring, Your (I assume) diagram above shows the snap ring hard up against the end, this is only the case then it's off the punp body I'd expect

[356RS]

When testing the movement of the support shaft (rod) it must be under a load, like bolted up to the MFI pump. Is this how you are testing it?

[BartdeBruijn]

1. So my new understanding is that there is a balance / equilibrium between the Thermostat spring and a spring in the pump
2. Because this balance the snapring is not contacting the house so the rod can move two directions.
3. When thermostat heats up /cools down the disc expand and the rod compresses via green lever spring A depending on the spring balance.
4. Now in my case when I mount my thermostat (as Mark suggests) not only spring A is been maximum compressed put also the rack is moving significantly (to enrich I guess)
5. Looking into the heat tube of the thermostat while mounting on pump I do not see the discs moving indicating that there is some balancing and that the snapring is not touching the thermostat housing so that the rod of the thermostat can move in two directions colder/warmer.
6. Concluding that the thermostat spring is very (to) stiff to push the package of discs back against the thermostat spring and moving the snapring from the thermostat housing..

   • The length of my discs and spacer package at roomtemperature is 71.33 mm.
   • The length of the rod sticking out of the housing (no spacer and cross shaped seal shim) is 16.8 mm.

Thanks for the input and answers but I decided I will do some more homework and reading first before throwing questions into the forum

[356RS]

The only time there is a balance/equilibrium between the thermostat spring and the pumps guide rod & spring is during a cold start warm up. The only purpose of the thermostat is to provide the correct amount of fuel enrichment during engine warm up. Cold running fuel requirements are calibrated by the thickness of the shims on the thermostats rod at the cap end between the 25 discs and main spring. Thicker shims = leaner fuel and thinner shims = richer fuel. During cold engine warm up, heat is generated up through the heat exchangers, then up to the MFI pumps thermostat. The 25 disc pairs heat up and expand causing the thermostat rod to extend onto the cam lever (your green) and down to the guide rod & spring which in turn moves the transfer lever & correction lever which moves the main rack into a leaner warming up condition and continues to the maximum expansion of the thermostats rod and stays that way for the duration of the warmed up running engine. Hope this helps.

[Henry Schmidt]

Simple way around all that nonsense........
Supertec cold start enrichment device. 4th generation, 25+ years of testing.
No raw fuel injection, no cumbersome heat raiser hose or special heater box attachment, driver/cable operated and it can even be tuned to offer high altitude compensation. Clean reliable and fool proof .....oops maybe fool proof is going a little to far LOL

[BartdeBruijn]

Henry,

I just like to understand how the thermostat worked.

The "Supertec cold start enrichment device" was already on my list for my engine build!
(great thing is that the MFI stays M(echinacal) with your device. It is even more mechanical as the Thermo part is eliminated ;-)

Thanks everyone for all the comments and explanations!
Bart

[Henry Schmidt]

Originally Posted by BartdeBruijn

Henry,

I just like to understand how the thermostat worked.

The "Supertec cold start enrichment device" was already on my list for my engine build!
(great thing is that the MFI stays M(echinacal) with your device. It is even more mechanical as the Thermo part is eliminated ;-)

Thanks everyone for all the comments and explanations!
Bart

Bart, I posted what I did because it seemed like you had your answer and I wanted to offer an alternative to the thermostat.
Like with most of what we do, pride sometimes gets the better of me.

I guess I should be on the lookout for trip hazards...... prov 16:18