I have added this article to my page as the American Jeepster Club site that used to host this seems to be defunct. If you are the author, please reach out to me so I can give proper credit to your work.
Re-printed from the Club’s newletter and only sent to club members
A member informed me on how to increase the heating output of the Jeepster heating system, and since most of us are not satisfied with the Jeepster heaters, I thought it would be worth mentioning.
First you are going to have to remove the entire heater assembly from under the dash. Do not forget to disconnect the control cables, fresh air duct and the two heater hoses located under the battery tray. Easy does it! Do NOT yank on the heater hoses. The nuts that hold the heater assembly are located at four locations on the firewall in the engine compartment.
Once the heater assembly has been removed, take notice to the far right side of the unit (passenger side). You will notice a flat area about 4×4 inches. Carefully cut this area out while leaving enough flat surface around the opening that you could adhere a temporary plate over the opening…for the summertime.
Now reinstall everything as it was and don’t forget to put new heater hoses on. Use a little WD40 or brake fluid to help push the heater hoses back on the heater core connections.
So, why does this work? Once you have the assembly out, take a close look at how the fresh air inlet is located to the heater core assembly and you will discover it is semi-centered over the top/middle of the core which means the fresh air is not being warmed up efficiently. But, by cutting an inlet in the far right side of the heater assembly bezel, the fresh air is forced directly through the heater core in a more efficient manner. One might even shut the fresh air vent off to help increase hot air output. Don’t forget to clean out the heater assembly before reinstalling it and make sure the fresh air intake seal that is located at the cowl is water tight.
Additional enhancements:
Another suggestion is to replace the near 30-year core with a new one, since you have it out, why not. Most major auto parts store can order it for under $45. Open up the heater assembly and remove the heater core and before inserting the new one, wrap some 1-1/2 inch foam insulating tape around the four edges of the core. This forces the fresh air through the core and not around it through any gaps between the assembly and core.
Another suggestion that I did on “Project Jeepster”, is to rivit sheetmetal over all the output ducts and then cut two circular holes in the bottom of the assembly. I then inserted two 90 degree angle ABS elbows which allow me to point all the hot air to me!