Hey guys, wondering how to approach this. I have below swim step exhaust outlets and at idle, or anything below 1800rpm, there is not enough water pressure to overcome the exhaust backpressure. Waterflow ceases and the temp will continue to rise approaching 200. Once underway or raising idle water will flow and temp will drop immediately. I am running a standard bravo water pump with a transom pickup, new impeller. Also have a recirculation water pump. Would a crossover solve this?

hopefully these pics help

Bumping, looking for insight. The exhaust is obviously going somewhere (out the below-water thru hulls) but seems as if the pressure from exhaust is causing a stalemate with the water pressure / introduction. Tempting to just go to a crossover and wondering if that will solve

Took the tstat housing off and have very strong flow there, as well as at the manufolds

Never heard of anything like you are describing. I don't see how it is possible that your actual exhaust vapors are causing a lack a water flow.

Do you have a water pressure gauge??
Post a pic of the transom

have to agree with Griff. there are 10's of thousands of boats with underwater exhaust that dont have this issue. you say you changed the impeller but did you also change the housing? going to a crossover is not going to change how the water goes out the exhaust so either you have a bad raw water pump housing or the circulating pump is not circulating properly which does happen.

Yup, water flow issue.
Lots of places to ck. Ck for most common, next most common, etc, etc…
I agree, always change impeller housing same time as impeller.

what engine are we dealing with and whats the compression ratio?most likely your gonna have to add water dumps above the water line and out the transom.

Water pressure in salt water at 2ft depth is 0.89 psi.

The exhaust system will flow at idle with npt much more than that..or whatever your discharge depth is.

As mentioned above...your raw water flow is restricted somewhere. Bravo'itis on the oxodised up raw water drive port?

When impellers fail, rubber pieces can get into your cooling system. Follow your pump outlet hose and take it off at the next connection. See if you have any rubber pieces lodged.
When I had this problem, I had pieces at the inlet of my oil cooler. Used a shop vac to get them out. Just enough restriction to warm up at idle.

I gotta agree with the rest of the group here. To put it in more scientific terms than Tartilla, the raw water pump flows a metric **** ton of water at idle and I don't see any way or how the exhaust set up is hindering flow. Problem lies somewhere between the transom assembly and output side of the pump.

Why a transom pickup? The standard bravo intake flows a poop load of water (assume the transom hose has not constricted)