Here's the adapter I made. That's a neat little push to connect fitting for 1/8" line. The thread is 10-32 straight with an o-ring seal. I already have a nylon line in the car from engine bay to the interior for various pressure and vacuum measurements so it's a matter of just plugging the nylon line into the 1/8 push to connect fitting and hooking up a pressure gauge inside.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Always carry at least one each fuel filters in your diesel-powered Mercedes-Benz products.

I've changed many a fuel filter a thousand miles away from my home-base more times than I can count. Most were changed on the dealer's lot OR the motel parking lot I managed to get the car to.

Fan belt, batteries, alternators, tires, fluid lines, etc. etc. etc. as well.....

The MB always gives an indication that it needs new filters.......HENCE - ALWAYS carry several with you at ALL times.

Looks good and neat. Let us know how things work out. So far I have been waiting for some clever member to come up with the best gauge position in the car.

Esthetically I just do not like obvious gauge additions. Some people like them. So my approach is installed in the glove compartment if practical. This gauge does not require constant observation really. Just checked periodically. Especially at speed.

My mind still tends to always wander back to the issue of improving milage beyond factory normal. Several times I have been beaten back. Since I tend to be somewhat stubborn from time to time. I persist.

Ideals are still surfacing as well from time to time. Of course so far they do not bear fruit. The mere fact that they still emerge means there is some possibility yet. I may not know my mind well enough but I am well aware how it functions.

By todays standards this is truly an archaic design. At the same time thats what it takes to make it easily manageable by people like myself. Of course at the same time I am aware impovement without a lot of money spent is an outside possibility at best.

Still the way my mind works would have ceased to produce approaches to this issue some time ago if there were not a remote possibility.

I realise I cannot sit down and engineer an approach. That was attempted by the manufacturer. Instead I have to take information of abnormalities observed over the years on many diesels and basically make them into something valid. It almost has to come from intuition. There seem to be clues that some gain may be possible still. Or I would have disgarded the concept long ago.

Tonite two new ideals occured out of nowhere. Thats why I posted this while it was fresh. One was what exactly would be the downside of operating a cast iron engine like the 616 and 617 engine at elevated temperatures?. Coolant with boil points a lot higher than todays currrently used anti freeze mixtures are out there.

Thermostats with higher opening temperatures might be sourced on demand from the ,Manufactureres or our current ones modified. I believe the base oil can survive and provide protection at somewhat elevated temperatures. Some newer four cylinder gas engines prove this. We have to get more btus released from the same amount of fuel in the combustion chamber. I would like to see the block temperature elevated perhaps twenty five degrees celcius.

Now before rolling around on the floor grasping your sides. I am well aquainted with the old indirect injection volkswagon engines getting a substantial boost in milage on hot days.

There might even be a member or two that observed this themselves years ago. Why did that happen? The air was hotter those days therfore by volume incoming air contained less oxygen. Yet oxygen is not the issue as diesels always have leftover. I now suspect the increased incoming air temperature was pushing the burn into another plateau so to speak.

I also believe unlike gas engines. It has to be some form of heating effect raising the btu output of the fuel in the volkswagon engines on hot days. This does not seem to transpire with the mercedes engines yet they are very simular in design in some ways. Fortunatly as stated there is a clue.

Volkswagon of that period had a heater output that could burn your skin. This was achived by a very different circulation arrangement especially designed for the head. This produced quick heat output on very cold days and scorching hot at the vents in a short distance from cold.

Some member should by memory verify this if they remember. I never had a gas car that could equal the heater output of most those volkswagons. Yet most diesels have poor heaters in comparison to gas cars.

A possible effect was the heads actual operational temperature might have been much higher than mercedes on a hot day yet the engine did not boil. For example the head might have been at 230-250F. Our mercedes heads may be at common block temperatures of 160 degrees on hot days. Someone should thermally scan an older volkswagon head on a hot day.

Since we cannot elevate the head temperatures on mercedes separatly as volkswagon did even though their heads were made of aluminium. We would have to increase overall operational temperatures. I think the oil is not a big concern of doing this within reason.

One reason at the time mercedes designed and built these engines would have been that no high temp anti freeze was available to my knowledge. Variations are out there today. . It would have no water component. Of some additional consideration is that this engine is an almost direct development of their first diesels other than material improvements. The design constant remained as fuel was cheap.

The unfortunate part is overall the mercedes diesel of the period has not got a large reserve capacity in the cooling system. So would the increased efficiency of the burn actually decrease the need for cooling? Less fuel is used for the same output as before. Would the differential of a hotter radiator to the ambient air temperatures increase cooling represented by greater transfer of btus to the air flow? Perhaps it is weak inneficient combustion that makes their cooling systems seem marginal.

Anyways I will dwell on this area a little. My guess still is from past experience if we could get the head operational temperature up milage would increase. Either by a gain in btus in burning in a hotter enviroment or just generally more force occuring from the speed of burn increase in a hotter enviroment. Or the core area of the burn changing in temperature gradients or charactaristics.

.I believe the valves could stand a moderate increase. Well I am not going to steal this thread. Just want people out there to roll it around in their minds a little. I will come back to this after considering it soon enough. The ideal is about 1/2 hour old or so at this point.

Under better burn conditions the relationship of energy output or force and generated heat are different I suspect. Or certain components quantifically different. More usable energy of the type we preffer is perhaps developed.

I have the banjo bolt/adapter installed at the IP inlet and gauge hooked up. At idle fuel pressure is 12 psi Cruising at 2500 rpm it is 14 psi. If I floor the go pedle it drops to 12 psi. I suppose the spring is weak on the pressure relief valve or I have a leak somewhere still? When I shut the engine off, it doesn't hold pressure and drops to zero psi within 30 secs. I think it should hold pressure longer than that. Should it?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Unknown territory on what to exactly expect on retained presure at shutdown I think. Perhaps removing the relief valve and cleaning it well and gradually stretching the spring till closer to 19 pounds will benefit. Just cleaning it could therotically help as you do not have to manipulate the spring that controls the pressure if you do not desire to. At least you are currently in the range of normal expected operating pressure from the factory.

Another test to possibly eliminate a lot of air in the system after car sitting for both an extended and short period. When cranking to start how quick is pressure developed and how much? It should be pretty fast I would think. Also remember if the filters are older they might be holding the base pressure back a little. Still I would not change them to check as they are in a safe range judging by your pressure indications..

Also when you drove at speed your pressure elevated a little further rather than declining. Indicating to me there is no major flow restriction or the pressure would have dropped I believe with the higher fuel and flow demand.

A lot of things you are going to learn are almost pretty new or the first time reported on site remember. So you will be able to help others. There are very few installations out there that I am aware of. I would not get excited at all by the 30 second drop off of presure at this point after shutting down. Lets see how a few other installations act to get a baseline.

Only two ways the pressure can drop with no fluid leaks obvious. Back throught the lift pump check valve or out through the relief valve on the pump.

It is perhaps unreasonable to expect those seats to seal perfectly at this point. Your installation is already informing you of what is transpiring in the system. How steady is your needle on the gauge. Any vibration of the needle to speak of?

Very neat installation on the banjo bolt by the way. On serious reflection why not grab a spare relief valve from a wreck or junk pump. You have the ability to experiment a little or the other valve just might seal better. Or not as well. Again it is going to take a lot of examples to prove what is possible with the leaking down of the supply pressure.

Here's a couple of videos of the fuel pressure gauge. First one is hot start on WVO (engine already at operating temp). As can be seen there's not much needle pulsation and pressure builds pretty fast. I guess the glycerine filled gauge is damping the lift pump pulsations. I can feel the pulsations in 1/8 nylon line however. There's almost no difference in fuel pressure between VO and diesel (there's dedicated filters for VO and diesel and both filters are the same p/n). Both filters have about 8K miles. I have a vacuum gauge at the lift pump inlet to monitor filter condition and both filters are still in the green. VO filter actually is at a lower vacuum than the diesel filter. I still have an air leak somewhere after eliminating the primer pump. After switching to diesel , shut down and upon restart I am getting a lot of air as indicated by the rough running and frothy fuel in the return line.

I pulled the fuel pressure relief valve from my 240D parts car and will take it apart to inspect and clean than install in the 300DT and see what it does.


CLICK TO PLAY!

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Accelerating from 2K rpm to 3K on WVO. Fuel pressure is increased slightly.

CLICK TO PLAY!

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Since my fuel system has been re-arranged where the fuel filters are before the lift pump (filters under vacuum, not pressure), I am not sure if the data I am providing will be applicable for a stock fuel system

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

D911, what size and kind of tubing did you use and how long was it? Not sure if this may be the difference but I used 1/8 o.d. nylon about 6 ft long to run it into the passenger compartment. It has a very small i.d. and very stiff that will not expand and contract with the pulsing fuel pressure. With a glycerine filled gauge, needle hardly vibrates. I even hooked up a boost gauge (non glycerine filled) to check accuracy of the glycerine gauge and the needle didn't vibrate that bad.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Chances are that there is air contained or trapped in your new line providing a rapid pulse absorbing or moderating effect. Another possibility is there is an air component in the pump doing much the same thing. The air is continually being resupplied from the lift pump in your case at this time.

I am actually hoping there is always a small pocket in the injection pump base that holds a little air always. Otherwise retained fuel pressure is a difficult concept that would require almost perfection. We all know there is not all that much perfection in the world.

The fuel filters before the lift pump will still enable the gauge to indicate decreased available pressure as they restrict flow over time. Air is never productive in the system other than the above I suppose.So it is always advisable to chase the ingress points down as you are.

It is at this point a bit of an unknown if a real tight system from the lift pumps valve to the relief valve can retain pressure. My feeling is with those two valves sealing really well. They might have been able to maintain it when these cars where newer. That may have been the norm in fact. It is possible.

I think in a little while we will know more about if we can restore that component easily .Or even if it was that way. My suspicion is a cautious yes but until we know.

Leakage when engine is off up through the elements in the pump should be discountable as the injectors pop valves effectivly close off the path. At very low pressures the injectors if in good condition may not leak down at all.

A car that can retain pressure in the injection pump base just might have an edge on really cold starting. The initial cranking gets a full measure of fuel flow from all the injectors.

It has to be a given that external air ingress has to be eliminated as well. We still have much to learn.

I have always wondered why a few examples of the 123 will start on days when many others also with good compression and glow plugs as well throw in the towel. The ability of some to have some retained pressure for long periods could be it. Or a big factor.

If things work out we might check the relief valves sealing ability by say putting ten pounds air pressure from a plastic line on the valve and dropping it into a container of water to see if there are any air bubbles at all. The lift pumps sealing can be eliminated if hard to manage by a simple check valve installed after it.

There will have to be some minor employed easily understood physics employed in testing for integrity. Only if early indications turn out well. Hopefully as always one thing will lead to another.

If some of you gentleman wish me to stop speculating and examing things from my perspective and methology say so. Since I learn many things from other site members I also try to contribute. Unfortuantly I usually arrive at conclusions by a very circular path.

This is both tedious and the road has many potholes. The end results are always an unknown when the trip is initiated. Not to start the trips does preclude any expansion of current beliefs and general knowledge. Or delays it.

I have found we all always learn something even if the end result is not as imagined. Contributions and efforts by many along the path change many things or the conceptial image of what is.

I did specify in posts and threads where I felt we where going and the areas that interested me quite a long time ago. I never expect anyone to agree with me at any point. Time in the past and hopefully the present vindicates this approach. To get even halfway to a potential goal will usually open avenues that eventually enable it. Or ultimatly will land up in areas never considered. There are few really dead ends if one remains mentally flexiable. The journey is still underway in my opinion.

I used my universal pressure tester on the 240D pressure relief valve. It opens at 15 psi. Took it apart and cleaned it till squeaky clean and shimmed it with 1/16" thick teflon. I punched a hole in the teflon, threaded an 8-32 screw in it as a holder and used scissors to trim it into a donut till it fits the spring seat hole of the cap. Pressure tested it and the shim raised the pressure to 20 psi.

Here's a video of the pressure tester using a bicycle pump.

CLICK TO PLAY!

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I installed the 240D pressure relief valve shimmed to 20 psi in the 300DT. I haven't taken it for a drive yet but the idle fuel pressure is definitely higher than before.
I think I also fixed the air leak. The in and out banjo bolts were a bit on the loose side. Snugged it up a bit. Tomorrow I will see if the filter drain back and air is gone.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I cannot see why not. Have to wonder if you will notice any difference in the drive at twenty pounds base injection pump pressure. Actually a fair percentage increase.. Is the idle any smoother at all? I suppose on vo it would not be as noticeable. There is a chance for the same reason power may not seem higher but it may.

At least your earlier pressure was not really substandard. If the car moves a little quicker or fuel milage seems a little better would be nice. Mention your impressions since many cars with the original relief valve would possibly have about your first mentioned pressure.

With the shimmed pressure relief valve, the engine is definitely more responsive and runs better. Idle is better also. Fuel pressure is higher per the gauge while driving but not 20 psi per the test gauge. More like 15 psi. I am going to add another shim to bump up the pressure a little more and see if there is further improvement. Maybe get a stronger spring if more shims don't get the desired results.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Well if 12 to 15 pounds made a noticeable differance even on vegetable oil. Them 15 to say 18 or 19lbs will make substantially more.

What you seem to have proven since variables are fairly well controlled. Even three pounds of base pressure increase is important. Because of the much slower burn or flame front with vegatable oil in comparison to diesel. I was not sure the differance would show.

I already knew it has a greater impact on diesel fuel. Really good information for everyone to know. The only variable that remained was your tightening up the banjo bolts. If the incremental gain continues with the further increase in pressure then that can be discounted to some extent. Your thread and postings should be watched by many. We can learn a lot just from your experiences.