Carver Owners Forum

OK. First update on the Run Dry impellers. Really easy to install due to increased flexibility. Thought I might get less flow with more flexible units, but just the opposite. There is a lot more water draining out the exhaust at idle at the dock. I installed new 160 T-stats. The engines are showing 168 -170 degree engine temp. Have not taken any real cruise yet, so we will see what happens at 3100 RPM for extended time. Gauges may be off a little, but they used to stick right at 160 level. I have seen reviews that engines are running about 8 to 10 degrees warmer with these impellers. More to come. er

If the impellers are more flexible, there's less pressure and could change the volume and affect temps.

Yes. The thing the is weird is if I have double the water volume coming out of exhaust at idle, would that not mean more water available to cooling system? What do you think about running at 170 degrees? er

170 is fine. You should confirm at the engine to make sure that's what she's actually running at and compare to the gauge. It will be a few degrees off because you're taking the reading from the outside with an IR temp gun.

Cooler wrote:Qr Bbpost Yes. The thing the is weird is if I have double the water volume coming out of exhaust at idle, would that not mean more water available to cooling system? What do you think about running at 170 degrees? er

Good idea IMO......The warmer you can get those engines/cylinder heads to run at the more efficient they will be all around. This applies to you cause you are in fresh water, but it still has to be kept within reason.....good luck.

I have a question though, in any of the material you read about these impellers, was there any mention of flow vs rpm graphs or comparisons ?

Small question, the advice/rule to check waterflow at engine start given earlier: is there a way to do that with stern drives, so the exhaust and everything go down in the water. Can't see or feel anything to indicate that the impeller is doing its job. I also have diesels, so can't make much of touching the impeller housing either: the whole engine shudders.


by the way: if you do see damage to the impeller; go search for the remnants!

There is a spec for the pump that indicates the volume over a period of time. There's also a method to check by noting the height of the discharge out of the discharge hose. These don't account though for restrictions that might be present in the engine and accompanying hardware. Taking temp measurements at key points on the engine and exhaust will paint a pretty good picture on whether there's a cooling issue or not.

American V8 iron is most efficient and was designed to run at 180-190F. No harm will be done running lower temps but efficiency suffers. That being said, all my previous V8 boats had 160F thermostats and ran pretty much dead on at 180 all the time in fresh water.

Salt water applications differ since there is more harm done due to salt crystallization within the cooling passages at higher temps and it is advisable to run 140f thermostats in this application.

Found this article that explains it better than I do. https://www.oceannavigator.com/saltwate ... -clogging/

Still not understanding why and how there can be more flow with the new impellers. There's the same displacement and same RPMs in the pump, right? I could see minor variations between impellers if some weren't sealing correctly as in worn or 'set' impellers) but not a huge change.

Also don't understand the temperature change. If it's raw water cooled and there's MORE water coming out the back that means there's MORE water that could be going through the engine, but the thermostat is opting for it not to go through the engine because it's staying more closed. Is it possible just the thermostat housing is staying cooler and "tricking" the thermostat to think the engine water is cooler than it really is? Where is the gauge temp sensor located relative to the thermostat?

My mechanic informed me of increased water flow. He said it is due to the higher flexibility of the blades, creating more suction. This came up when I shared my thoughts with him regarding a more flexible impeller. I thought I would get a little less suction, but he was right! Gauge temp sensor is pretty close to the t-stat housing. The engine is cooling, just running 8 to 10 hotter than when I ran with standard impellers. er