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.