I am planning the do a cooling system maintenance on my 1998.5 and have not been able to find the correct thermostat for it . The ones that I have been handed are the large one for the 12 valve. I did try one about 7 years ago and had such wild swings in temp that I thought I had done something wrong. After much thought and trouble shooting I found that the thermostat did not look like what I removed ( my fault I did not compare them when I removed the old one). I went back with the old one and finally found one that matched. Here I am 7 years later and the only one that I can find is for the 12 valve and in their data base it said that that is the only one fits from 89 to 09 which I know is wrong.The stant pn 14289 or 46289 for the heavyduty but I could not contact anyone at stant but I did contact a gates tech support and he said that stant makes theirs but he has not got back to me yet. The picture shows the difference with the one on the left is the correct one. I have been to every place I can think to find one including cummins dealers  within a 100 mile raduis and they all pull the 12 valve one. How are the rest of you finding yours. I even ordered one from Rockauto that had the correct picture but when it showed up it was the 12 valve.

36 minutes ago, Doubletrouble said:

 At 15psi between the filter and vp44 you will still get return fuel through the vp44 like you would normally.

 @Mopar1973Man was saying that the Raptor type pump (mine is the 150) will regulate the pressure by rerouting the excess fuel above 15psi back through the head of the pump.

Ok got! Makes since.  Thanks! 

At 10 PSI the overflow will be closed, by 14 PSI the overflow is fully open. Still in all reduced volume because of the small port. This will aid with cooling and lubing the pump. Won't do anything for the lift pump and churning issues. There needs to be 3rd line back to the fuel tank to allow free flow of the used fuel being the volume of the lift pump requires a 1/2 inch return to the tank.

 

Carter stock

Airtex

Raptor

Mechanical pumps (belt driven).

FASS smaller series

 

All these have same issue because no 3rd return line.

 

AirDog 100/150/165

FASS 100/150

 

These two pump do have a 3rd line to return to the tank.

6 hours ago, Mopar1973Man said:

All these have same issue because no 3rd return line.

I sure thought the mechanicals had a regulator with a line back to the tank.

No. The mechanicals are just two lines in and out. No return.

9 hours ago, Mopar1973Man said:

All these have same issue because no 3rd return line.

I sure thought the mechanicals had a regulator with a line back to the tank.

 

I guess the website wants me to reply again... Why does it do this?

Anyway, @IBMobile had a lost back around 2019 and mentioned a regulator. Was that aftermarket? Those are PD pumps and could blow the system apart without a regulator. Is it internal?

The kits show a return for the filler neck, what's it for if not pump return?

So confused.

45 minutes ago, LorenS said:

I sure thought the mechanicals had a regulator with a line back to the tank.

It does.  There is a bypass valve which is the pressure regulator with the return line going to the filler neck.

The valve/regulator is not internal.

In my opinion, there is a lot of incorrect information being posted here.  

 

15 hours ago, Threadzy said:

So no fuel passes through the relief valve at the VP back to the tank? 

 

I am assuming you are referring to the 14 psi overflow valve in the VP44,   The moment the engine starts and idles, there is approximately 19 gph of fuel instantly flowing through the 14 psi overflow valve and returning to the fuel tank.  This flow is provided by the VP44 internal fixed displacement vane pump - NOT the lift pump. 

 

If the lift pump pressure is 5 psi or 20 psi, the 19 gph return flow will remain the same while the engine idles. If there was no lift pump and the internal vane pump was drawing directly from the fuel tank, there will still be 19 gph fuel return flow from the VP44.  The internal vane pump pressure regulator is set to around 135 psi - certainly more than enough pressure and flow to ensure that the high pressure pump chambers fill and that fuel flows through the 14 psi overflow valve.

 

14 hours ago, Mopar1973Man said:

Doesn't matter. It's a restricted flow if you pull the banjo out and look at the port in the VP44 it small. No 150 GPH your only using 2.5 GPH at 55 MPH at 20 MPG in the VP44 injected. So the other 147.5 GPH is routed from the outlet of the Raptor back to the inlet, churning the fuel and creating cavitation. This is roughly speaking not counting limited VP44 return

 

At 2000 rpm there will be about 28 gph of fuel returning to the fuel tank via the overflow valve.  That is certainly much more than the 2.5 gph injector consumption. 

 

It is also likely that if the lift pump pressure is around 15 psi, then the lift pump flow will be much less than  rated 150 gph.  The lift pump manufacturers do not provide flow vs pressure performance charts.  The most information that I could ever find was from FASS  - which stated that the rated flow was at 0 psi.  So, I would not be surprised if that 150 gph rated lift pump is only flowing half of that rating at 15 psi.  If this were the case, 75 gph minus 2.5 gph minus 28 gph equals 44.5 gph returning from the lift pump to its own inlet, or returning to tank by separate line.

 

11 hours ago, Mopar1973Man said:

At 10 PSI the overflow will be closed, by 14 PSI the overflow is fully open. Still in all reduced volume because of the small port.

 

Not true if you are referring to 10 psi lift pump pressure.   At 10 psi (or 5 psi, or 20 psi), 19 gph of fuel will be passing through the 14 psi overflow valve and returning to tank with the engine at idle.  The only time the 14 psi overflow valve is closed is when the engine is shut off.

 

I made these charts below to illustrate the combined series and parallel fuel circuits involved in the VP44 fuel system. The 19 gallons / hour of fuel returning to the fuel tank from the VP44 is based on return flow tests that I and others have performed.  The test is at engine idle.  The circuit on the left uses a 60 gph / 6 psi lift pump that returns fuel to its own suction.  The circuit on the right uses a 100 gph / 17 psi lift pump that uses a separate line to return fuel to the tank.  Compare the different flow rates in some parts of the two circuits.  Note that the return flow rate from the VP44 does not change in either circuit.

 

- John

 

 

 

 

 

 

 

This is exactly what return checking on my lift pump has proven. What is important is return to tank from the overflow valve at the vp, my return flow is huge at 6psi lift pump pressure 

 Tractorman makes a good presentation and want to say that there are some good things have developed around the 19 p.s.i. inlet pressure concept worth noting.  The idea of keeping the vp running cooler with more pressure/ volume, right or wrong, afforded more room to add some degree of needed restriction from a proper filtering system, in some cases, polishing of the fuel. Other benefits was the almost continued discovery of the in tank screens found clogged, creating the need to eliminating them all together, again supporting the need for correct filtering that properly collects the sediment without clogging by easily changing out every so often. Right or wrong, this goal of consistent higher inlet pressure prompted many to relocate the lift pump to the frame thereby eliminating the two poor locations of the factory lift pump. One was on the engine block constantly shaking and absorbing engine heat. The other was the location of the lift pump in the tank which is a terrible option for obvious reasons. Third was the relocation of the draw straw or relocation of the return fuel. Either way, allowed hot return fuel to cool before being sucked back into the already hot injection pump. So far we know higher inlet pressures haven't hurt anything and the side effects of this idea have become a benefit in many respects.

 

I must be getting old, I needed a very strong cup of mud to write a simple paragraph!

 

 

@JAG1, I appreciate your response.  I strongly agree with most of what you are saying.  But, I am not challenging any of those things.  In fact, I have done some of the things that you mention - mounting my lift pump on the frame rail, modifying the suction line inside the fuel tank, adding a serviceable coarse suction strainer just upstream of the the lift pump, and rerouting the return fuel flow to the fuel tank filler tube.

 

What I am challenging is the long-lived belief that somehow the lift pump pressure determines how much return fuel (cooling for the VP44) comes from the VP44 via the 14 psi overflow valve.   Over the years I have read many posts from the leader / leaders of this site who have referenced that if lift pump pressure is less than 14 psi, then there is no return fuel flowing over the 14 psi overflow valve, thus no cooling for the VP44 injection pump.  I have also read many posts that say the VP44 will be damaged if the if lift pump pressure is less than 14 psi.  It is my opinion that this is simply not true.  I have never seen any documentation to support these beliefs.

 

I have performed fuel return flow tests that dispute this concept.  Others have also performed this same test using flowmeters and driving their trucks for real-time documentation.  Some of the tests were performed and results were posted over 15 years ago.  In fact, one of the testing events involved a vendor that was going to market improved lift pump systems, but dropped the idea when the fuel return flow test results were documented.

 

One of my goals for posting this information is to help the readers decide what fuel system is best for their truck and to help the readers diagnose any fuel related problems.

 

Years ago I attended a truck driving school.  The school was taught by veteran truck drivers, each with over 30 years of safe driving experience.  Toward the end of the training I was talking with one of the instructors.  I was thanking him for the knowledge he shared.  One thing that stuck in my mind was something that he said.  It was something to the effect of, "You can learn a lot from a veteran truck driver - including any bad habits or misconceptions of the trade.  So, don't be afraid to challenge what you hear"   That has always stuck with me.

 

I am hoping that my challenge will be addressed.

 

- John

 

 

John it is cool what you say. I think so much of the importance for higher inlet pressure was influenced by the many reports in diesel forums when a poster would post about lost fuel pressure, in my case dropped from 15 down to 3 psi and a short time after got the death code for the VP44, 0216 code and companion code of 1693. I think that in itself started everyone on a path to understanding properly lubricating and cooling the VP.

 

A side note; I can say for sure that getting out and camping is an important aspect of life prior to winter setting in Everyone is invited to meet up, just let us know and you will be contacted by PM.

And back on subject. I installed one of the 12 valve thermostat late yesterday and went for a drive of about 35 miles on the 2 lanes around me. The thermostat did not open until 200 degrees and stayed open untill 178 degrees and swung up and down for the hole trip reading off my Scangage2 that is mounted on my dash. This morning I installed a different 12 vale thermostat that I had  but not been installed. On this trip I also went on the freeway ( 70 MPH) and it did hold the temp steady at 70 MPH but but varied just the same below 55 MPH. I thought that maybe I screwed something up so I reinstalled the old thermostat and everything is back to normal. Something that I did notice with the second 12 valve thermostat was that the dash temp gauge reaction was so slow that if that was your only gauge you would never see much temp change. Because I have gotten so used to the Scangage2 the only dash gauge that I look at is the oil pressure.

@Nekkedbob, I apologize for my part in hijacking your thread.  

 

- John

 

not a problem . You have some good info.

 So @Nekkedbob, which thermostat was it that you decided to go with? I changed mine a year or so ago and noticed a temp fluctuation even just sitting at a trafic light on the factory gauge in the dash. I didnt feel it should flucuate that much but maybe so?

2 hours ago, Doubletrouble said:

 So @Nekkedbob, which thermostat was it that you decided to go with? I changed mine a year or so ago and noticed a temp fluctuation even just sitting at a traffic light on the factory gauge in the dash. I didn't feel it should fluctuate that much but maybe so?

Wow, that's way different than mine! Watching the OBD live data, I saw that my gauge wouldn't move off vertical until 215 degrees.  Aren't the temp gauges in these trucks just a step up from dummy lights? Or maybe that's just oil pressure and my gauge is the one that's worn out!

From what Ive read the early 24 valves had a real oil pressure gauge. I know that the graduations are useless but on the early ones that the dealers didn't get questioning oil pressure they do go up and down with temp and RPM. I have got mine hot and if done over a longer period of time the temp gauge does read as close as can be expected. I am still running my old thermostat until I find the correct one. I still have the one that I removed 6 years ago that was working (stashed under my seat with spare sensors and filters). I have a different ones coming from Cummins and NAPA Tuesday and I will find out if they are correct.

And just a FYI I know that Ford was doing the dummie gauge as early as the 70s on the vehicles that had oil pressure gauges. I had 2 different trucks made in the 70s and after on oil pump shaft sheared in off in my first one I got digging deeper then I wanted and found that it was a common thing.

Oil pressure is near correct but there is a few small tweaks I've found. Like Volt Gauge if it reaches 12.00 it displays correctly. But as soon as it hits 11.99 Volts then the gauge drops to 8 volts and trips the check gauge light. Same with Coolant Temp if it passes 230*F it will swing to far end and trip the check gauge light. I've check my oil pressure against a mechanical gauge its correct. The only time it will skew is if the high idle is used then the oil pressure shows high when the coolant drop to 123*F but other than that it shows correct. 

Well I got a different thermostat from a Peterbilt dealer today and it looked like a  stant but was a 180 degree unit so I didn't take it and they don't spec a 190 degree for the motor that the parts guy could find. I am waiting on one from Napa. I found a good parts man finally that can dig deeper in their catalog then any one else that I have seen. I should see the new one by Thursday as it was coming from Tennessee.