Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 08-02-2017, 07:17 PM
Banned
 
Join Date: Jul 2008
Posts: 146
Bypassing Fuel Thermostat for Better Performance

I have a leaking fuel thermostat on an 87 300d OM603.
Instead of fixing it, I have temporarily bypassed the thermostat. Runs fine, no issues.
So I had an idea to reroute the fuel lines so that the fuel is always running through the heat exchange circuit. Full time winter and summer.
My thinking is that warmer diesel fuel will be more efficient with more power year round. (theoretically)
Or is there a sweet spot for fuel temperature?
Am I thinking wrong? What say ye?
Reply With Quote
  #2  
Old 08-02-2017, 07:40 PM
Diseasel300's Avatar
Registered User
 
Join Date: May 2016
Location: Texas Hill Country
Posts: 3,898
Bypass the fuel thermostat (go straight from the tank to the lift pump) and be done with it. Unless you live in Siberia, it isn't really doing much anyway. Plumbing the fuel through the heat exchanger full time is detrimental to your injection pump. Not only does hot fuel have less power density (it expands), but hot fuel also has less lubricity so you're tearing up your lift and injection pumps.
__________________
'11 Honda Accord EX - "The Daily" 64K
'83 500SL Euro - "The Money Pit" 116K
'86 300SDL - "The Diseasel" 186K
The Diseasel Thread - Everything You Didn't Know You Wanted To Know
Reply With Quote
  #3  
Old 08-02-2017, 07:59 PM
Registered User
 
Join Date: Dec 2006
Posts: 2,770
Quote:
Originally Posted by Diseasel300 View Post
hot fuel also has less lubricity so you're tearing up your lift and injection pumps.
Not true.

Effects of High Temperature and Pressure on Fuel Lubricated Wear
Reply With Quote
  #4  
Old 08-02-2017, 08:24 PM
Registered User
 
Join Date: May 2009
Location: The slums of Beverly Hills
Posts: 5,798
Quote:
Originally Posted by David Wilson View Post
I have a leaking fuel thermostat on an 87 300d OM603.
Instead of fixing it, I have temporarily bypassed the thermostat. Runs fine, no issues.
So I had an idea to reroute the fuel lines so that the fuel is always running through the heat exchange circuit. Full time winter and summer.
My thinking is that warmer diesel fuel will be more efficient with more power year round. (theoretically)
Or is there a sweet spot for fuel temperature?
Am I thinking wrong? What say ye?
On my 87 I bypassed the thermostat, ran it through the heat exchanger full time and no heat exchanger full time, couldn't tell any difference. Since I'm in a hot climate it's all bypassed now.
Reply With Quote
  #5  
Old 08-02-2017, 08:30 PM
Registered User
 
Join Date: Dec 2016
Location: San Diego, CA
Posts: 51
I agree with the general sentiment of just bypassing this device, and run the fuel hose directly to the prefilter --> lift pump. I have the exact car you do, and I've bypassed this on my car, and on two previous 190D's without issue. I'm also tempted to bypass the redesigned version on the om606 engine. Really not needed if you live in location with a more temperate climate. Also, this gives you an opportunity to really clean up and reroute the fuel and coolant hosing in that area to make it look much more streamlined.
Reply With Quote
  #6  
Old 08-03-2017, 09:11 AM
Registered User
 
Join Date: Sep 2007
Location: Calgary Alberta Canada
Posts: 1,098
"So I had an idea to reroute the fuel lines so that the fuel is always running through the heat exchange circuit. Full time winter and summer"

But that's how it came stock perhaps you are refering to removing the fuel thermostat which regulates the fuel temperature?

I ran a 617 for 22 years with outdoor temps into the -40's without a fuel heater or additives. The challenge isn't keeping it running but starting it can be. My current 602 has the fuel heater I rebuilt it 8 years ago just because but it likely would operate the same without the heater even in extreme cold.
__________________
92 e300d2.5t
Reply With Quote
  #7  
Old 08-03-2017, 12:16 PM
WTB: 94/95 E320 Wagon
 
Join Date: Oct 2007
Location: Charleston SC
Posts: 2,456
I say spend the $10 on the parts to fix the thermostat and put everything back to original spec. I did that job on my '87 wagon with dealer parts about 11 years ago, and it is still running just fine.
__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~380k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 379k miles
'73 Balboa 20 "Sanctification"
Charleston SC
Reply With Quote
  #8  
Old 08-03-2017, 07:11 PM
1985 190d
 
Join Date: Nov 2006
Location: canadian border vermont
Posts: 478
Anybody who has ever poured diesel fuel in freezing temperatures will agree that it gets noticeably thicker. Maybe in San Diego it doesn't matter, but I think the fuel preheater might be useful elsewhere.
Reply With Quote
  #9  
Old 08-03-2017, 08:53 PM
Squiggle Dog's Avatar
MBCA Member
 
Join Date: Jul 2008
Location: Surprise, AZ, USA
Posts: 2,852
What cracks me up about the fuel preheater is that it seems that the time you need warm fuel the most in a cold climate is during starting. But, the engine is still cold then so the preheater doesn't start working until after the engine has warmed up, but by then I imagine the fuel has already been heated to some extent by the radiant heat from the engine compartment. And then the rest of the year, while the engine is running, the fuel is getting too hot.

I suppose that the preheater could be useful if a block heater is utilized, and if it in fact heats up the coolant that is in the heat exchanger so the fuel will be warm before starting.
__________________
Stop paying for animal enslavement, cruelty, and slaughter. Save your health and the planet. Go vegan! I did 15 years ago. https://tryveg.com/

DON'T MESS WITH MY MERCEDES!


1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 344,000+ Miles
Reply With Quote
  #10  
Old 08-04-2017, 12:13 PM
Banned
 
Join Date: Jul 2008
Posts: 146
It looks like there are no performance gains in the summer with heated fuel.
And there may or may not be an advantage to having heated fuel in the winter months in areas that actually have a winter.
It will occasionally get down to 5-10 degrees F in my area.

So I will spend the $10 on parts to make it not leak.
I guess I can put the thermostat in the freezer and see if it works as it should. Don't really want to spend $35 on that part.

Thanks for all the input.
Reply With Quote
  #11  
Old 08-04-2017, 12:49 PM
Registered User
 
Join Date: Sep 2007
Location: Calgary Alberta Canada
Posts: 1,098
The fuel heater thermostat is included in the $10 parts kit.
__________________
92 e300d2.5t
Reply With Quote
  #12  
Old 08-04-2017, 01:05 PM
Banned
 
Join Date: Jul 2008
Posts: 146
Quote:
Originally Posted by dieselbenz1 View Post
The fuel heater thermostat is included in the $10 parts kit.
Please post a link if you can. I only saw separate parts.
Reply With Quote
  #13  
Old 08-04-2017, 02:09 PM
Registered User
 
Join Date: Sep 2007
Location: Calgary Alberta Canada
Posts: 1,098
Way too long ago to recall any links.
__________________
92 e300d2.5t
Reply With Quote
  #14  
Old 08-04-2017, 02:32 PM
Registered User
 
Join Date: Sep 2007
Location: Calgary Alberta Canada
Posts: 1,098
Here's a link for the parts but you may have this already

OM601, 602. 603 Diesel fuel thermostat REBUILD parts list
__________________
92 e300d2.5t
Reply With Quote
  #15  
Old 08-05-2017, 02:56 PM
Banned
 
Join Date: Jul 2008
Posts: 146
Quote:
Originally Posted by dieselbenz1 View Post
Here's a link for the parts but you may have this already

OM601, 602. 603 Diesel fuel thermostat REBUILD parts list
Yes, that's the list I saw. Not available as a kit. O-ring and cap are inexpensive. Thermostat not so much.

Thanks
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 02:39 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page