Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it throttle

[Uraijit]

So yea, like the title says. I can idle or keep it around 1000 RPM and it stays in the green all day. As soon as I give it any real throttle, I can literally watch the gauge climb.

I'm guessing it's a restriction. Impeller has less than 6 hours on it. Don't know the history on the risers. When I had the engine out, they were a little rusty, but not too bad. I scraped off all the rust and the few flakes that there were, so I don't think they're bad.

The water pickups are clear of debris...

If the engine water pump was bad, would the outdrive pump be enough to keep things cool at idle?

Tomorrow I'm going to back-flush each part of the system. Any suggestions on anything else to check while I'm pulling hoses (besides the obvious, checking condition of the hoses)?

 

[ziggy]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

a kink in the water hose from the transom to the bell housing?

water pocket cover leak?

debris from old impeller at tstat housing?

debris from manifold or riser? i understand ya cleaned em. but if they needed cleaning, perhaps ya missed some in the water jacket where ya can't reach? or loosened some rust somewhere cleaning it and it fell off later after the clean...

did ya replace the waterpump housing when ya did the impeller. my first impeller i did didn't work out as well as it could have. replacing the housing helped on the second try...

i think there's more. but can't remember them.... i've seen a list or two posted, but can't find it....

 

[sarantis]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

leave the water pocket as the last thng to check.it is hold at its place by 4 steel bolts fited in aluminium which means big helectrolysis.In my effort to take them out i broke all of them no matter the heat i used and it took me 2 weeks to open new threads!The service manual refers tothe quantity of water you have to get disconnecting the input of the therm.housing at 1000rpm and for 15 seconds .So sometimes it's good to refer to your engine!

 

[chiefalen]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

You have a heat exchanger? Clogged up common problem.

Flapper broke loose?

 

[sarantis]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

Sorry i noticed that you state your engine .I 'll send you a chart later

 

[ziggy]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

leave the water pocket as the last thng to check.

i found a water pocket cover leak during flushing of old impeller pieces out. while flushing from the ft. to back. upper and lower separated. as i was flushing it. you could see water leaking at the gasket....

agreed on breaking off the bolts though. i only broke 3.... i figure it took me 40hrs to acquire tools that would do the deed + drill and tap them to helicoils.... big bummer of a job that probably has a low success ratio would be my guess... don't touch the water pocket cover unless ya really got no choice..

 

[Don S]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

Check the inlet to the power steering cooler. You would be surprised at what you can find there. Especially if you have the tube bundle type cooler.

 

[45Auto]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

Is an MC-1 similar to an Alpha? I've seen the same thing in an Alpha where they didn't put the drive key back in the impeller. Apparently it had enough friction on the shaft to pump at idle but slipped as engine speed went up.

 

[Uraijit]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

Thanks for the suggestions everybody! The weather was crappy so I didn't get around to working on the boat today. Shooting for tomorrow for sure, cause we've got plans to go camping on the lake--which isn't much fun unless you've got a boat...

The impeller housing was replaced with the impeller. The key was installed, of this I'm 100% certain.

This is a new problem that developed last time I was out. The engine ran perfectly cool before now.

I do indeed have the tube style heat exchanger/power steering cooler, so I'll give that a close look.

Where exactly is the exhaust flapper on the MC-1 setup? Is it at the base of the Y-pipe, or is it somewhere in the bell housing?

 

[littlebookworm]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

On my previous boat, with a 350 Mercruiser, MC1, I had a similar problem. It was perfect at the dock, even at high RPM. When I went out on the water, she overheated. Replacing some of the hoses with clear plastic showed that I was getting air bubbles into the system. Turned out be an over-tightened water pump cover which had distorted and was sucking air once the boat was on plane and the pump section was out of the water. I's suggest you double check the pump installation as well. Good luck. Hy

 

[Uraijit]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

Okay, so I pulled every hose off the engine, and back-flushed them all. I even opened the drains on the block, and flushed those out. Got quite a bit of crud out of them, but not enough that it should have affected the cooling.

I'm getting great flow through the drive.

No obstructions anywhere, that I can find.

Thermostat is opening.

Still, I'm not getting very good flow out of the thermostat housing.

When I pulled the hoses off the exhaust risers, with the engine running there was no water coming out of the hose that feeds the riser. The exhaust blew a considerable amount of water out of the riser. Does this indicate that the exhaust is restricted, or is this normal?

I put a running water hose into the risers (with the engine off), and it seemed to flow fine, but there was no exhaust pressure (cause the engine was off), so I guess that doesn't indicate much.

There never was much flow out of the hoses feeding the risers, while disconnected, so it seems like the problem could be the engine water pump?

What do you guys think?

 

[chiefalen]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

Pull the water pump. Any vanes left on it, clogged up? Find the clog got to be one.

 

[Uraijit]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

The pump was just off when I re-sealed the oil leak. I guess it's possible that I jogged something loose in the water pump that was enough to plug it up. I'll take it back off and pull it apart.

Does a marine water pump have a weep-hole, like an automotive pump, so you can tell if the seals are shot?

 

[Uraijit]

Re: Engine stays cool while under 1000 RPM Temp shoots up as soon as you give it thro

Okay, I think I may have found the problem. I pulled the pump, and the gasket maker sealant that I used had squished out into the water passage, and was blocking about 30% of the pump passages. Makes sense that this would be the problem, since the trouble started after pulling the water pump to re-seal the timing cover...

I cleaned it up, and I'm going to use a real gasket to re-install it.

I went ahead and pulled the cover off the pump while I had it off. The impeller is very rusty, but still intact.

I'm going to take it back up and put a water hose though all the water passages again tomorrow, to make sure it's all cleared out (I don't have a water hose at my apt).

Hopefully this fixes the problem. Thanks for your help, guys!