2002 Mercury 150 EFI overheat

I have just purchased a boat with twin 2002 150 EFI's. (400 hours all fresh water ) both water pressure guages read 2-3 PSI at idle, and dont get much above 5-7 psi at 4000 RPM. I changed both impellers with complete kits with no change. A long idle will cause an alarm that im assuming is overheat warning as it goes away with a throttle bump. At 1000 RPM it will idle forever with no issues.

The tell tale stream does get hot, but im not sure what that temp should be.

These is my first boat with outboards. Im used to BBC so any help/advice would be appreciated.

I have now replaced both T Stats, Poppet valves and temp senders. I still get the overheat at long idles in gear. Any thoughts as what to try next?

How about a few pictures of the rear of your boat and engine installation, especially having to do with the height of the antivent. plate vs the hull at the "tilt" position you use when running slow and having the problem.

Let me know if you need any different angles,,,,,, hmm,,, wont upload the pictures for some reason

I normally have the drives tucked all the way in while idling

I don't have a drop box account and it will not let me open your pictures.
My son's 150 had 143F pellets on his stats. 143 is the Normal Position temperature of a US domestic hot water heater....hot and might be some steam. The OT alarm is 195F with a small tolerance. That would surely have a lot of steam since at sea level pure water boils at 212F.

Since both are doing the same thing I suspect that something has happened that affected both engines equally....like running through and ingesting weeds, or a lot of shallow water operation where sand was kicked up and ingested. Do you have a bore scope? Harbor Freight has them for a great price. Might get one and pull your tstats and have a look around your cooling passages in the blocks.

What did the impellers look like when you removed them....any missing pieces of blades?

Ingestion was my first thought as well. The impellers were perfect, but I still back flushed every port I could find, and have used my blow guy through every hole. I have great flow out the tube with the lower unit off when I use the flush port by the tell tale outlet. The motor is 100% clear. I disconnected the temp sending units last week in a " damn the torpedo's moment " and ran the boat all day with no issues. I have located my scan tool with a smartcraft chip since our move. I need to hook it up and see if it works with outboards or if I need another cartridge for it.