High water pressure and engine overheating

[sawblade723]

Hi guys, a while back I posted about high water pressure in my 1986 Merc 150 XR2(15psi @ idle & 30+ @WOT). It was suggested that I verify my gauge accuracy so I purchased a new pressure gauge and added a temp gauge. Today I took it out and the new gauge reads the same as the old one and the temp gauge went to the center of the movement @ idle and pegged on hot after about 30 seconds after hole shot. I backed off the throttle to idle and the temp went back to center after a minute or two. I have recently installed a complete water pump, new t stats, new poppet, new head gaskets, new exhaust cover gaskets. The old water pump was distorted like it had been very hot. While I was replacing the gaskets I checked for any blockage in the water ports and everything looked fine. I'm running out of ideas and really need the pro's on here to help me troubleshoot this thing. Thanks.

 

[TahoeQ4Pilot]

Re: High water pressure and engine overheating

What about your impeller, when was the last time it was replaced?

 

[sawblade723]

Re: High water pressure and engine overheating

I installed a new complete water pump a couple of months ago. New housing, base, gaskets and impeller. Thats when I started getting the high readings on my water pressure gauge.

 

[Chris1956]

Re: High water pressure and engine overheating

That's a tough one. That Merc should never have good water pressure like that. How much water does she pump? My '93 Merc V6, pumps a ton of water, but with low pressure. When running on the 'muffs, she will suck every last drop, hose at medium on.

Let me ask a dumb question, where are the temp and pressure gauges installed in the motor? I had to tee the pressure gauge into a hose, since no port on the head was usable, as they already had sensors. Do the temp sensor alarms work? When the gauge shows hot, can you touch the heads w/o burning yourself?

 

[sawblade723]

Re: High water pressure and engine overheating

The temp gauge is hooked to a sender that is in the port side head. The pressure gauge has a barbed fitting in the top of the block that the hose hooks to. The alarm system no longer works, thats why I added the gauges. When it is at idle the block and heads feel hot but you can touch it for few seconds before it gets painful. It only overheats while running fast so I have not been able to touch it then. I do know that when the gauge shows HOT there is steam coming from the motor so I believe the gauge is true.

 

[Fisher freak]

Re: High water pressure and engine overheating

have your heads pressure tested it sounds like it could be cracked.

 

[Bondo]

Re: High water pressure and engine overheating

I installed a new complete water pump a couple of months ago. New housing, base, gaskets and impeller. Thats when I started getting the high readings on my water pressure gauge.

Ayuh,... were there any Missing pieces from the old impeller,..??

 

[sawblade723]

Re: High water pressure and engine overheating

The old impeller was intact. It was hard and bent to the shape of the the pump but it was all there. I pulled the heads and exhaust cover to look for clogged ports but all looked good there. I have read that a bad gasket at the exhaust plate or a bad water tube seal can cause these symptoms. Can anyone confirm this before I go tearing into this thing on a wild goose chase?

 

[j_martin]

Re: High water pressure and engine overheating

The old impeller was intact. It was hard and bent to the shape of the the pump but it was all there. I pulled the heads and exhaust cover to look for clogged ports but all looked good there. I have read that a bad gasket at the exhaust plate or a bad water tube seal can cause these symptoms. Can anyone confirm this before I go tearing into this thing on a wild goose chase?

One time I hit an old rotten log and pretty well sawed it in two. Then my engine did what yours is doing. I Had to pull the exhaust cover and heads and clean all the splinters and chips out.

Your problem could be caused by debris in the engine (thus the question, where is the old impeller) or if it's been worked on wrong parts or gaskets in the baseplate. Long story short, something is impeding normal water flow from the engine.

hope it helps
john

 

[AFR Engines]

Did you ever get this figured out?