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 > Tech Help

LinkBack Thread Tools Display Modes
Old 01-22-2002, 11:33 AM
Tump's Avatar
Registered User
Join Date: Jun 2001
Location: Westchester, NY USA
Posts: 183
Head Gasket Replaced -- MPG drop -- Questions

Dear Fellow MB nuts,

I posted this as an update to my Head Gasket thread, but since this has now evolved into a seperate question, I'm reposting it here as a new thread.
Regarding my 87 300E with about 160,000 miles (or more) that through November, 2000, used 1 to 1.5 quarts of oil every 1500 to 2000 miles depending:

I did some research and found that the camshaft and stem seals were replaced in 1994, 7 years or approx 100,000 miles ago. Before doing my head I replaced the radiator, expansion tank and overflow tank myself, flushed the cooling system and still after 3 weeks found oil reappearing in the coolant.

So I had the head gasket replaced and the head redone with new Stem Seals, etc. During the job it was found that one pre- cat in the OEM exhaust was completely clogged and fused with oil (the metal mesh surrounding the cat fused to the inside of the pipe) ( I checked this myself and tried after the mechanic did to dislodge this mass with a screw driver -- it would not budge). Apparently, this is where the oil was leaking to. In any case I replaced the header and pre-cat to cat system (its one OEM piece) with a stainless piece manufactured to OEM spec.'s by TimeValve without pre-cats (the new cat I'm told is sufficient to pass inspection -- we will see). This whole job was expensive (I bought my own parts and had the specialists do the work (@$80/hr) coming in for a total cost at a little under $3,600.00. Not bad however for a new header-cat system, remachined head and stem seals, replaced stem guides, timing chain and timing chain tensioner. The head bolts were within spec.

The car performs amazingly well now, is much quicker and smooter, etc. and burns no oil whatsoever at this point. Job was done 1 month ago. But, after averaging 19 mpg before the job for 6 months, the car now is averaging 17 mpg since the job -- the mechanics' claim to be baffled and they readjusted my air fuel mixture (without charge). Readjusting the mixture did not seem to solve this decrease in mpg.

Do you guys have any ideas or suspicions as to why my car dropped 2 to 3 mpg from its previous average when is should be 2 to 3 mpg better -- at 20 to 22 mpg (as per MB rating on this car 20 city 25 highway)? (I do drive the car a little more agressively -- but drive the same roads the same distances and use the same gas and gas stations).

Rebuit and restored Obsidian Black/Palmino Interior '87300E with Euro Headlights (they are amazing). Wanted OEM 8-Hole 16" Rims with decent tires.

Reply With Quote
Old 01-22-2002, 11:55 AM
Posts: n/a

The oil you were burning probably made up for the other 2 mpg.
Reply With Quote
Old 01-22-2002, 12:17 PM
Registered User
Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,804
If the pre cat was pretty fouled, you may want to do a voltage/cycle time test on the 02 sensor. That may be as badly
fouled as cat was.
Also, seeing the head was done , ask if any silicon gasket material was used anywhere.
Reply With Quote
Old 01-22-2002, 10:29 PM
Registered User
Join Date: Jul 2000
Posts: 638
where did MPG go? look to the head!

What did you do to the head? Face the gasket surface? If so, you removed some metal that is equivalent to more than 100,000 miles of timing chain stretch/wear, and the cam timing is probably several degrees late- unless you carefully checked it and put in the offset camshaft key(s).

A real common oversight with aluminum head overhead cam engines is resurfacing just the head gasket surface without also resurfacing the top side at the same time to ensure the two sides remain perfectly parallel. This required completely stripping the head (removing all the guides, cam towers, etc.

The heads are very flexible, and often seem 'bowed', or even twisted when laying there in the open, but straighten out when torqued down. Unless the head WAS perfectly true and a uniform amount of metal was removed and the top and bottom sides maintained parallel, you now have cam journals that are no longer perfectly aligned. You will have to add shims (see the parts counter) under each bearing tower to get them back in place. A tight cam can consume a surprising amount of power to turn. It should be possible to turn it by hand when the head is torqued down (without the rockers or chain installed of course.)

Reply With Quote


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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Head Gasket and other items on 300SDL tstarr Diesel Discussion 12 07-10-2004 11:44 PM
e420 head gasket markE420 Tech Help 3 06-12-2002 09:46 PM
Tackling M103 head cyl gasket (need expert tips) pmizell Tech Help 7 12-27-2001 04:54 PM
Head gasket replacement MarkM Diesel Discussion 16 11-02-2001 01:07 PM
190E 2.6 & head gasket issues myronbecker Tech Help 3 03-24-2000 01:00 AM

All times are GMT -4. The time now is 02:01 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2021, 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