300xs Overheat but Good Water PSI

[BlazerVA]

1. 1E053040
2. 2016/Mercury/300xs
3. 29p Bravo xs
4. Never ran over 5500 but could go over 6000 at wot
5. Idle 2-3 psi. wot 19psi
6. Smartcraft

Made a 30 minute run this morning with no issues. Fished a few hours. Started the motor up to run elsewhere. Got up on plane and the overheat alarm popped on. I came down to an idle and checked the temp and water psi. Temp dropped to 128 almost instantly and psi was 3lbs. Thought i had picked up some grass. Went at it again. This time i watched the temp go from 128 at 3500rpm to 140 with in 10 seconds. I hit the throttle some and got to 5k rpm and the temp dropped to normal. Got to a dock and checked the lower unit for any visual blockages and found none. Next run the motor did the exact same thing. I noticed when I hit the throttle the temp would go to normal. Water pressure was never low at any point. Got home and pulled the thermostats and poppet. Poppet looked ok but didnt open smoothly. One of the thermostats had a piece of wood stuck in it. I put them in hot water til it opened and cleared the debris from it. Also flushed the motor with the stats out and poppet out. Now all that said my question is can the poppet cause the motor to overheat if its not opening properly? I know it can cause low temps but can it cause high temps? Thanks in advance.

[Savage]

When was the last time the compressor strainer was cleaned??

What was the temperature of the motor when it overheated?

[SilverFox579]

In addition to Savage's questions, the poppet should move smoothly, as if buttered, as Don would say. And it can most definitely cause engine to overheat if not operating correctly.

[BlazerVA]

When was the last time the compressor strainer was cleaned??

What was the temperature of the motor when it overheated?

As far as i know the strainer hasnt been cleaned. I'll do it today. Honestly didnt realize it could be til I read the forum last night.
The overheat was at 160 degrees. Only happened once but the temp would jump around unless i got on the throttle. Then it would stay between 128-131.

[BlazerVA]

Just pulled the strainer and it was full of grass, mud and other gunk.

[Savage]

Yep...better flush the adapter plate out really good .

[BlazerVA]

Got it all flushed out. Ordered a new poppet kit and thermostat gaskets. Hopefully this fixes the issue. Ill find out Thursday when i get everything. Thanks for the help.

[Savage]

I would leave the poppet alone for now. The strainer and flush will correct your problem.

[EuropeanAM]

One other item- WHEN was the water pump last replaced? If you are overheating... especially overheating and found any form of debris in the system, don't overlook the water pump (all that crap had to pass through the pump).

[BlazerVA]

One other item- WHEN was the water pump last replaced? If you are overheating... especially overheating and found any form of debris in the system, don't overlook the water pump (all that crap had to pass through the pump).

I pulled the LU today. Everything looked good but I replaced the impeller and seals since I had it apart. Also pulled the thermostat hoses and compressor water outlet hose and ran water through them to make sure they were clear of debris. Hopefully this fixes the issue. I won’t know til Saturday when I can get it to the river.

[BlazerVA]

Should the telltail be warm coming out? Mine is about room temp. I know it comes outta the compressor but should it be warm?

[SilverFox579]

Will only be as warm as compressor can make it, from my engine I'd describe it as lukewarm at best depending on water surface temp.

[EuropeanAM]

Telltale (on this engine) will normally be lake water temp or up to 20 degrees above lake water temp.

[BlazerVA]

[bucksbass]

Yep...better flush the adapter plate out really good .

I'm not familiar with flushing the adapter plate. Can you give a brief description on how to correctly do this?
Thanks

[Savage]

Remove the strainer and flush adapter plate with water. Motor is off and lower cowling removed.

Can also back flush with the flushing port (see owners manual).

[BlazerVA]

After flushing, changing poppet, impeller and cleaning the strainer problem is still there. Ran fine all day til the run back to the ramp. At about 3k rpm the temp started to rise. Got to 150 degrees. I punched it and it dropped back to 128 and stayed there. Is there something Ive overlooked?

[Champ 2001]

I hate to say this! But, it COULD be a Powerhead lower gasket? Its what mine was. Hopefully I am WRONG! Did you check the Thermostats?

[BlazerVA]

pulled them also. Is there a way to check before pulling the powerhead off?

[EuropeanAM]

I'm wondering if it's not simpler than that- perhaps as simple as aerating the water supply at a particular throttle/trim setting.

What's your P-T-P measurement, and which Blazer is this engine on?

Still running the 1.75 TM Gearcase, and if so, do you have any of the side water inlets plugged off?