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                                                                EXHIBIT 10(a)(6)

                         CORE MOLDING TECHNOLOGIES, INC

                            UNSECURED PROMISSORY NOTE
                                 ---------------

$200,000.00                                                   December 29, 2003


       FOR VALUE RECEIVED, Core Molding Technologies, Inc. (f/n/a Core Materials
Corporation), a Delaware corporation (hereinafter referred to as the "Company"),
hereby promises to pay to the order of International Truck & Engine Corporation
(f/n/a Navistar International Transportation Corporation), a Delaware
corporation (hereinafter referred to "International," which term shall include
any subsequent holder hereof), the principal amount of Two Hundred Thousand and
00/100 Dollars ($200,000.00), together with interest thereon calculated from the
date hereof in accordance with the provisions of this Unsecured Promissory Note
(this "Note").

       This Note is being issued in connection with the payoff of that certain
secured promissory note executed by the Company and delivered to International
on December 31, 1996, as thereby amended from time to time.

1. PAYMENTS OF PRINCIPAL AND INTEREST.

   (A) PRINCIPAL PAYMENT. The Company shall pay the entire principal balance of
this Note on December 31, 2004.

   (B) INTEREST. Except as otherwise expressly provided herein, interest shall
accrue at the rate of eight percent (8.0%) per annum, (computed on the basis of
a 360-day year and the actual number of days elapsed in any year) on the unpaid
principal amount of this Note outstanding from time to time from and including
the date hereof until the date paid, or (if less) at the highest rate then
permitted under applicable law. The Company shall pay to International all
accrued interest on this Note on December 31, 2004.

2. PREPAYMENTS.

   The Company may, without premium or penalty, at any time and from time to
time, prepay all or any portion of the outstanding principal amount of this
Note, provided that the Company has first paid all accrued interest on this
Note.

3.  MISCELLANEOUS

   Payments of any amount required hereunder shall be made in lawful money of
the United States or, as Noteholder, in his sole and absolute discretion, may
accept. All payments of any amount required hereunder shall be credited first
against collection of costs, if any, thereafter against accrued but unpaid late
charges, if any, thereafter against accrued but unpaid interest, if any, and
thereafter against the unpaid balance of the principal amount.

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   The Company agrees to pay Noteholder all costs and expenses, including
reasonable attorneys' fees, paid or incurred by Noteholder in connection with
the collection or enforcement of this Note.
   This Note shall be governed by, interpreted under and construed and enforced
in accordance with the laws of the State of Illinois. Any action to enforce
payment of this note shall be filed and heard solely in Dupage County, Illinois.


   IN WITNESS WHEREOF, this instrument is executed as of the day and year first
above written.


                           CORE MOLDING TECHNOLOGIES, INC



                           By: /s/Herman F. Dick, Jr.
                               ----------------------
                               Herman F. Dick, Jr.
                               Treasurer and Chief Financial Officer




Accepted and agreed to
this 29th day of December, 2003



INTERNATIONAL TRUCK & ENGINE CORPORATION



By: /s/ T. M. Endsley
    -----------------
     Name:  Terry M. Endsley
            ----------------
     Title:  Vice President & Treasurer
             --------------------------



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