Do I need to plumb the steam ports on an LS swap?
Yes. On most LS engines the thermostat sits low, on the water pump, instead of up top like older small- and big-blocks. GM added steam lines in the cylinder heads to vent trapped air and keep hot spots from forming at the top of the engine. Leave them open or capped and you risk air pockets and hot spots.
Your options:
- An LS swap radiator with a steam port: most LS conversion radiators have one. Run the steam line to it.
- A universal or original radiator: use an adapter with a steam fitting. Speedway's LS swap radiator hose adapter (listed at $24.99 in its article) fixes both problems at once: a 1/4 in hose barb takes the steam line, and it adapts the LS water pump's 1-1/4 in upper outlet to the 1-1/2 in inlet on a typical radiator.
See the accessory drive guide for pump choices.
Confidence: medium — sources disagree or are limited; check the sources below.
Community discussion
Related questions
- Best LS swap radiator
- LS steam vent: do I need it?
- Can I cool an LS swap with a stock-style radiator instead of an expensive LS conversion radiator?
- What hose sizes and routing tips simplify LS radiator plumbing?
- Which water pump should I run for an LS swap: truck pump or Camaro pump?
- Where do I route the LS steam vent line on a square body swap?
Sources
- LS Swap How-To Guide — Speedway Motors
- How to Choose the Best Radiator for LS Swaps on a Budget — Speedway Motors
- LS Swap Radiator Hose Adapter with Steam Port — Speedway Motors