I need to buy a replacement cap for a West Bend coffee percolator Model 54159

Try the West Bend site itself.. they should have one for your top:
click here: https://westbend.com/collections/coffee-makers-parts

Also try Bed Bath and Beyond: click here... https://www.bedbathandbeyond.com/store/product/harold-import-co-replacement-percolator-top/1062316651?skuId=62316651&mrkgcl=609&mrkgadid=3022660732&utm_source=bingpla&utm_medium=cpc&utm_term=Brand%3D&enginename=bing&mcid=PS_bingpla_nonbrand_coffeetea_&msclkid=b7a06f2bc10315da0c73320c9f0d7855&creative=77721843472849&device=c&matchtype=e&gclid=CIbFrvuSsuMCFVPTswodo1wDLQ&gclsrc=ds

check with appliance repair shops in your area online search using make and model or check with manufacturer

check with the manufacturer / service agent as to the thermostat setting
as it is getting hot , the element is working but there are now safety regulations that prohibit water over 80 degrees c so the thermostat may be set at the correct temp allowed by law

the thermostat isn't holding long enough to get the desired heat any longer,, it needs replacement , the parts are hard to locate, and then you need to have it replaced, so I guess it depends on if you want that done, or just get a new 12 cup one at target for around 40 bucks http://www.target.com/p/West-Bend-12-cup-Coffee-Percolator/-/A-12408458 I tried searching for the part you need, But was unable to locate it

The West Bend Large Capacity Coffemakers do not use replacement filters. The manual for the West Bend 33600 Large Coffee Urn is available here:

http://www.westbend.com/supportdata/L5613B_LargeCapacityUrns-All.pdf

Use an electric perk or regular grind coffee in the percolator basket rather than a 'drip' or finely ground coffee that would require a filter.

If you require a new basket, please see the West Bend on-line replacement part site here:

http://www.westbend.com/catalog.cfm?dest=itempg&itemid=946&secid=87&linkon=subcategory&linkid=125

if you can find the model number for your product you should be able to order a replacement handle from Ihe following site:

http://www.westbend.com/catalog.cfm?dest=dir&linkid=125&linkon=subcategory

Sorry someone has not responded sooner.

from my research it runs at 1,000+/- watts

http://www.amazon.com/dp/B0036WS1FA/ref=asc_df_B0036WS1FA1051652?smid=ATVPDKIKX0DER&tag=nextag-kitchen-delta-20&linkCode=asn&creative=380341&creativeASIN=B0036WS1FA

contact west bend customer service 866-290-1851

Ask here, the can get you virtually any West Bend manual.

http://www.abtecparts.com/westbend.htm

Try this to order all of your part needs !