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                                                                     EXHIBIT 5.1

                       [LETTERHEAD OF COOLEY GODWARD LLP]

December 28, 1998


MOTORVAC TECHNOLOGIES, INC.
1431 S. Village Way
Santa Ana, CA  92705

Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection
with the filing by MOTORVAC TECHNOLOGIES, INC. (the "Company") of a Registration
Statement on Form S-8 (the "Registration Statement") with the Securities and
Exchange Commission, covering the registration of an aggregate of 933,426 shares
of the Company's Common Stock, $.01 par value (the "Shares"), including 120,000
shares for issuance pursuant to the Company's 1998 Stock Compensation Plan and
331,492 shares for issuance pursuant to the Company's 1998 Employee Stock
Purchase Plan, 50,000 shares for issuance pursuant to the Company's 1996
Director Stock Plan, 325,000 shares for issuance pursuant to the Company's 1996
Stock Incentive Award Plan, and 106,934 shares for issuance pursuant to the
Company's 1994 Stock Incentive Award Plan (collectively, the "Plans").

In connection with this opinion, we have examined and relied upon the
Registration Statement and related prospectuses, the Plans, the Company's
Certificate of Incorporation and Bylaws, as amended, and the originals or copies
certified to our satisfaction of such records, documents, certificates,
memoranda and other instruments as in our judgment are necessary or appropriate
to enable us to render the opinion expressed below. We have assumed the
genuineness and authenticity of all documents submitted to us as originals, the
conformity to originals of all documents submitted to us as copies thereof and
the due execution and delivery of all documents where due execution and delivery
are a prerequisite to the effectiveness thereof.

On the basis of the foregoing, and in reliance thereon, we are of the opinion
that the Shares, when sold and issued in accordance with the applicable Plan,
the Registration Statement and the related prospectus, will be validly issued,
fully paid and nonassessable.

We consent to the filing of this opinion as an exhibit to the Registration
Statement.

Very truly yours,

Cooley Godward LLP



Jeremy D. Glaser