454 Mag still overheating...
 

Need some advice from the collective:

A few threads back, I posted about overheat conditions with my '89 454 Mag. Removed the thermostat, cleaned and flushed system, etc. I thought I had it licked, but today the problem was as evident as ever.

Idle and low RPM, engine runs around 160. On plane and loaded, I can go about two miles with the temp steadily increasing to about 210.

When I got back to the ramp today, I tried an experiment. While still in the water, att 1000 rpm I pulled the inlet hose for the thermostat housing. I found good water flow. When I increased rpm to approximately 3000 rpm, I had no water. Let me correct that... I had some water, but definitely nothing like at idle and in more of a pulsing fashion. What the hell is causing that? The other day, a friend also mentioned that he could see the circulating pump hose pulsing and collapsing (I added a spring to make sure it cannot collapse).

What am I dealing with here? One idea has been to pull the hose going to the inlet on the pump, and to put my garden hose directly in it, clamped, to see if it would maintain flow.

Interesting observation from last weekend to this one... last weekend, the engine would idle at just about 120 degrees (no stat) while on the hose. Even reving the engine wouldn't change it. This weekend, idle temp was at 150.

If anyone has any ideas, I'm all for it. A suggestion was made that the drive/transom might be clogged and to add a thru-transom water pick-up.

Thanks,
Tom

I had the same exact problem on my Bravo equipped Checkmate. The gimble housing is more than likely corroded and it is collapsing the suction hose where it passes through the housing. Pull the plastic barb and look at it with a mirror/light etc. Its a weekend job, pull engine to repair.....OR cap it off and install a thru hull!

One of your hoses is probably collapsing under the suction.

Post #2 Bravo Fever Check this had the same deal

Looks like a thru-hull pickup is in my very near future. Everything else has been either replaced or inspected as good so this has to be it.

Sometimes there is just some crud under the plastic fitting at the top of the transom assy that needs to be cleared out. This can be as simple as removing the two bolts and the fitting and taking a screwdriver and clearing this out - maybe backflush it into the drive. I would look at this before I went to the trouble of installing a thru-hull fitting.

Also, that suction hose going into the seawater pump has multiple layers of rubber. It is possible that this hose is breaking down and the inner layer is collapsing under suction. Your idea of providing positive pressure with a garden hose might tell the tale here. You could compare water flow with positive flow here to water flow with the drive pickups by getting a big rubbermaid tub and filling it with water with the drive let down in it. Just some things I would try to diagnose the problem before assuming that the drive / transom assy is corroded up and changing to a thru-hull pickup.

Going to try ruling out the transom-to-pump hose with a garden hose tonight. If it maintains water pressure to some degree, then I'll know it's in the transom assembly. I may go ahead an change to a thru transom just to get it over with.

If you pull the hose off the transom assy and feed it direct with a garden hose, it will run cool for sure. I pulled my hair out over this same problem. Best of luck and post results!

Sure sounds like a collapsing hose on the gimbal.
On garden hose you are adding pressure to that line, keeping it from collapsing on you. In water, the hose collapses.
Good Luck

I've seen this same activity on the muffs. What I'm trying to do is see if it could be a bad hose going to the pump. I'm pretty sure it's the transom, but I'd like to rule out the hose.

I had a similar situation when I replaced my water pump rubber piece but didn’t replace the housing. It seems that when I would get to a higher rpm it was starting to overheat. I don’t know what actually happened to fix it but I replaced the pump and housing the second time and never had a problem again.

I ran another test last night...

I replaced the water hose from the transom to the pump. Started engine with the hose off the inlet into the manifold... good water at idle. Bumped to 1200 RPM, good water. Bumped to 1500, good. Bumped to 1800. No water. Brought back to idle. Still not water. The only way to get water was to shutdown the engine and restart.

At lunch I'll connect the garden hose to the inlet of the pump and see what happens.

Any thoughts on the above?

Thanks!

Yes.....same thoughts as before.


a. Sea pump housing, inspect or replace. A worn housing will lose pressure and volume at higher rpm

b. Transom water intake. At the very least remove the drive and fish something through the hole in the bellhousing to check for blockage.

I know that you have already flushed the system but what do you mean by that? I ask because it could mean different things to different people. I don’t know where you boat at but on the Missouri river where I do most of my boating it’s not uncommon to get corn husk and other floating debris stuck inside the cooling system and usually right at the oil cooler, when this happens you need to take the hoses off and flush them individually and not just a general run the water through from the thermostat housing. It’s worth a shot at this point.

Update...

Pulled the transom to pump hose at the transom. Shoved my garden hose down into it pretty good and fired it up. Removed the inlet from the manifold. I had good water at idle and no water back-flowing from the garden hose connection. Increased RPM to 1k... good water. Increased to 1500 or so and water was flowing then stopped. When it stopped flowing, water was gushing from the garden hose connection (not sealed but shoved about two feet in... definitely saturated the pump).

What would cause that? To me this would say the pump is the issue.

Running out of ideas. Impeller and housing??

At first I was hoping it was a problem with the exhaust... blockages, etc. Not the case. Everything is clean. Water flow from the inlet through the exhaust is good. The problem is ahead of the pump or the pump itself.

remove the hard hose from the impeller pump to the transom and inspect the inside or better yet replace it. Then remove your sea water pump and inspect the housing and impeller or better yet replace that too. If it is in good shape then you have a spare to keep incase you blow one on the water. Also, like suggested before remove the inlet hose of the oil cooler and get a mirror in there to make sure it is clear. Rather than inspecting one thing and trying again, then tearing apart again, check what people are throwing out there.

Did that yesterday (hard hose). Also inspected all the lines, cooler, etc. They're good. I guess it's on to the pump.

pump stops pumping. won't re start until you quit spinning it . it is the pump. check the impeller. it could be slipping on the shaft and stops turning at a certain load...

I'm confused, when I run hot the first thing I look at is the impeller, then the housing.....I am assuming this is the same for most boaters? I am not sure how you got steered in the direction to check everything else first

The impeller and housing are cheap... With all the issues you've had they are likely damaged at this point, 4bus is right! Start there by simply replacing them. Also a lot of guys have mentioned running a hanger or something through to clear any blockage a general flush won't get, do that and replace the thru transom hose. Whole deal won't be $100 and you'll know for sure if it's your pump or not when you are done.

Are you absolutely sure you have the right impeller shaft diameter on your impeller? It sounds like the rpm causes the shaft to start spinning inside the impeller..

The impeller was replaced in June. That's why we were looking elsewhere. Trying the new pump in a few minutes.

While you have it off do yourself a favor and backflush the oil cooler and lines that go to the pump from the thermostat housing before you put the lines back on just to make doubly sure there are no old impellar pieces in there.

Did all of that. The lines are all clear.

I installed the other pump, fired it up on the hose and waited. Pulled the thermostat inlet hose and had plenty of water. Increased rpm, still plenty of water. More rpm, plenty of water. I quit at 3k. Lots of water. Looks like a bad pump. I'm going to take it apart to see what's what. For now, it would appear to be fixed.

Thanks for all the suggestions everyone!

change seals on old pump housing. check shaft for grooving. previous impeller may have knicked seal.