Heater Motor, S1, Alternative

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S1 Alternative Heater Blower Motor

As the OEM motor from the S1 Heater Assy is no longer available (and was £160 from Lotus when it was), an alternative is to use the blower motor assy from an 1990's Landrover Defender (RHD to chassis LA939975). Part number is RTC4200.

Buying one of these from any of the on-line LR parts specialist/ebay, gets you a motor manufactured by GATES (as is the OEM Lotus one) with a new plastic fan which also fits the Lotus, and the LR mounting plate (to be discarded). The LR motor is virtually identical to that on the S1, bar the welded on mounting flanges are in a different place.

S1 Fan Case on LHS. LR RTC4200 on RHS
S1 Fan Case on LHS. LR RTC4200 on RHS

LR Assy on LHS. S1 Assy on RHS
OEM S1 Motor on LHS. LR Motor on RHS

You can clearly see the motor mounting flange difference in the photos above

It is not possibe to use the LR mounting plate coupled/bolted directly to the S1 fan case as the extra thickness of the LR mounting plate fouls the chassis in the front compartment. ((( Only discoverable when you try to refit the whole heater assy to back into the car for the first time !!!!! ))).

Instead remove the LR motor and fan from the mounting plate (which can be discarded) and mount the LR motor to the existing fan case.

The LR motor must be mounted with the mounting flanges in a "Y" shape, as shown in the photo below ( The LR mounting plate is clearly still attached in this photo).

Position of LR Motor Flanges wrt S1 Fan Case

NOTE. If you try to use the existing motor mounting holes in the fan case to mount the LR motor, the LR motor mounting flanges will once more foul the chassis leg. ((( Yes. I did have to strip the whole thing out for a third attempt at fitting !!!!!! ))))

New mounting holes for the LR motor flanges require to be drilled in the fan case and spacers are required to compensate for the difference in mounting flange positions between the OEM motor and the LR motor

The OEM motor was rivited to the fan case. Once new holes were drilled, I used M6x40 bolts from the fan casing outwards and nyloc nuts to bolt the motor to the spacers.

The spacers I used were some thick walled tubing I had to hand. They need to be 30mm high, (shorter than ~25mm the plastic fan fouls the heater matrix assy, longer than 35mm the plastic fan fouls the fan case).

LR Motor Mounted and Spaced on Fan Case

An alternative is to use nylon or plastic spacers readily available on ebay.

The LR motor comes with a molded on connector (you can see it on some of the photos above). I could not find supply of a loose mating half so cut it off and wired a waterproof Amp Tyco 2 pin Superseal Waterproof connector in its place. Good for 25A and used on lots of automotive applications


The black wire from the LR motor should be connected to +12v (orange) from the fan resistor cable

The LR RTC4200 assembly is available from many many LR Parts stockists online/ebay. It's manufactured by Britparts and will cost about £80 inc VAT (Feb 2014). You can buy the same part from LR for double that amount !!!! I checked and the LR part uses the same GATES motor and is most probably supplied by Britparts.

If your desperate for cheapness, there must be a lot of LR Defenders sitting in scrap yards, but anyone who has taken out an S1 heater matrix knows its a pig of a job , so I'd seriously suggest you do it once and just put a new motor in.

And finally I had to laugh as the LR motor comes mounted with rubber insulators clearly to dampen out the motor vibration..... A Land Rover Defender with more of a nod to noise reduction than the original S1. Got to love Lotus.

NOTE Since writing this article, another SELOCer has discovered the LR motor (ie it still has the flanges in the wrong place compared to the OEM S1 motor), can be bought directly from this site.


Gate Motor 12v MP5620 from THSS Ltd

At Feb 2014 prices, it was £89. Dearer than the LR part (and without a fan), but that may change in the future

I've not used this motor, but it does look like the LR part