over heat

[tomschauer]

Hans, so you are saying they work for a while and lose prime while under way? Very Odd.

Just something to check, I replaced my MerCruiser pump housings and impellers this year. The genuine MerCruiser pump kits came with new bolts and washers. While I was assembling the pumps, I noticed the bolts bottomed out before they actually sealed the impeller housing to the pump tightly. I was able to slide a .030 feeler gauge in between the pump and the impeller housing. Probably wouldn't have caught it if I did it on the boat, but I had them at home. Put the original washers back in (they were twice a thick as the new ones) and a nice tight seal. I am sure I would have had a problem if I installed them the way they were.

Hopefully you can find your gremlins soon!

[Viper]

Pep, assuming your pumps are okay according to your observations, and that you've checked for leaks throughout the intake circuit, it doesn't leave many more possibilities. As mentioned in a previous post, clogged coolers can cause this issue as well. If the main heat exchanger looks clear, the oil coolers could have marine growth causing intermittent issues. You'll likely have 2 per engine. I know it's a longshot but have you ensured your seacocks are open all the way and have you confirmed there's nothing blocking them?

Do your engines have fresh water rinse ports (a hose on the starb side of the engine with a blue cap on it) on them? If the caps aren't tightened properly, you'll suck air.

Chances are your strainers are Perkos. They use either cork or rubber seals which are easily available. The seal size will will depend on the model (port size) of the strainer.

I'd also like to know which model pump you have. Post engine serial numbers and exact engine model, I want to check the pump model and see if there are any cooling related service bulletins.

[pepmyster]

Hi Viper. serial numbers are 401212383, then I believe 4. I'm going to replace, hopefully if they have, the strainer top gaskets. Yes, the fresh water service port caps are nice and tight. When I did run the engine using the fresh water port, engines ran fine. Must be losing it's prime somewhere, that's why I'm going to replace the gaskets.

[Viper]

I'm coming up with an "invalid serial number" Check again, and give me the exact model number as well because several models will pop up. They may all use the same components but best to be exact. If you don't have that, let me know, I'll have to get the info somewhere else.

[pepmyster]

8.1 Gii-E
3869278
4012121383
2004

[Viper]

That’s more better!
No bulletins stand out for cooling issues and I don't see any incomplete campaigns on that engine. There was warranty work but unrelated.

Here are a few more things I’d be asking considering what you’ve already checked, some of which you may and may not have thought about. It’s a lot I know but a lot are things we usually don't think about. We can only help if questions are answered so we can follow a proper diagnostic process.

- Is your pump an all metal unit or does it have a metal housing but plastic inlet and outlet ports?
- Is the bracket/stay attached to the pump and is the rubber stop lug intact or does it show signs of having overheated?
- Has she ever overheated in the past?
- Any dripping from the pump?
- Is the shaft seal inside the pump in good shape? This is a replaceable part.
- Is the o-ring in the pump installed properly and has it ever been pinched? This would be evident as a section would be flattened instead of round.
- When you replaced the impellers, did you touch the hoses? To confirm, the top hose port is typically the intake and the bottom is the discharge to the engine.
- Are you certain the pump housing isn’t warped? It’s not always noticeable but easily occurs with improper winterizing or running dry.
- Do you have the Neutra-Salt flushing option?
- Are ALL hoses fastened with gear clamps, are there any fastened with crimp type clamps?
- Are you sure of the amount of coolant you have in the engine? Should be close to 26 litres plus the hot water exchanger circuit where applicable.
- Has your coolant been tested? Should be a 50/50 mix. Has the coolant been changed recently? If so, was it added slowly, then engine run between 1000-1500 rpm with NO load for at least 5 minutes? The system is self venting/purging but must be filled properly then topped up as required to the level between the “Min” and “Max” indication marks on the overflow bottle.
- Are there any leaks around the heat exchanger? I believe you have the vertical type. Check for leaks at the hoses, around the top cover, and the top cover bolt.
- Have you verified the temps at the block? Is it in fact overheating when your gauges say it is?
- Is there a steady beeping alarm around 200 deg F?
- How did you winterize the engines? Did you run antifreeze through the strainers so that it passed through the pumps?
- While running, have you sprayed hose connections and the strainer with soap to see if bubbles get sucked in? This is a sure sign that you’re sucking air and may not be noticeable otherwise.
- Have you hooked up a diagnostic tool?
- Anything obvious in the data during an overheat event?
- Have you checked for fault codes yet?
- Engines running properly? Last time tune-ups were done?

The exhaust system can affect cooling also and there’s things to check there but it's getting late so go through the above first.

[pepmyster]

Thank you for the list! I will be heading to the boat this morning. The only seal I had for the impeller housing was a med size for the housing itself. Number 3.

[pepmyster]

Here we go. Checked all again. Removed the impellers for inspection again. Perfect. Check flush out caps, perfect. No leaks, water, anywhere. Check flow from strainer after removing the cap. Great flow when sea cock open. Look at the gasket on strainer cap. Gasket looks not really centered. No rubber gaskets at marina supply. Take the gasket and flip it to test since the underneath looks brand new. Started up engines, I can actually see movement in the strainer baskets. Could not get them to overheat. See photo of gasket from the port side.

[Viper]

You took her out for a sea trial?

[tomschauer]

Hopefully you have solved it!!!