Hope this sheds some light on the matter
This an excerpt from AOPA's website:
This is a summary of the most commonly asked Certificated Flight Instructor (CFI) questions. For more information or clarification, call AOPA Aviation Services, (800) 872-2672.
Q: Can a CFII with single-engine only privileges on his/her instructor certificate provide instrument instruction in a multiengine airplane?
A: Yes, if the instructor also has multi-engine privileges on his/her pilot certificate. The instructor privilege "Instrument-Airplane" is not category and class specific and may be used for any type of airplane, as long as the instructor has these privileges on his/her pilot certificate. Note that in this case, the instructor is limited to instrument instruction only in a mult-engine airplane.
Q: Can a CFII with single-engine only privileges on his/her instructor certificate give an Instrument Competency Check (ICC) in a multi-engine airplane?
A: Yes, if the instructor also has multi-engine privileges on his/her pilot certificate. The instructor privilege "Instrument Airplane" is not category and class specific and may be used for any type of airplane, as long as the instructor has these privileges on his/her pilot certificate.
Q: Can a CFI with single-engine only privileges on his/her instructor certificate give a flight review in a multi-engine airplane?
A: No, since a flight review requires 1 hour of flight instruction. To provide flight instruction, a flight instructor must have appropriate category, class and type (if appropriate) privilege on his/her flight instructor certificate.