Mercruiser 496 HO Low pressure, high temperature problems
#1
Registered
Thread Starter
Join Date: May 2012
Posts: 56
Likes: 0
Received 0 Likes
on
0 Posts
Mercruiser 496 HO Low pressure, high temperature problems
The boat: 2008 Formula 350 SS (dual engine)
Engines: Mercruiser 496 HO Seacore (w/ Axius)
Drives: Bravo III
Exhaust is captains call (not sure if that could matter)
I bought the boat last September and quickly realized this was a problem. I had a 1999 330 SS (w/ fresh water cooled 454s) before this and I figured it would be a simple fix like a bad impeller. After the battle of getting my pump out (those green and white flush hoses are too short!) I found the impeller was in great shape but there was some serious "swirl damage" to the housing which I learned is from sand/rocks getting stuck behind the impeller. To remedy this I bought a rebuild kit from http://www.marine-496pump.com. Unfortunately this still didn't solve the problem. Here's the symptoms I'm seeing:
Port water pressure: 4-5psi
Port temperature while cruising: starts around 162 and then slowly climbs to 167-175F
Starboard water pressure: 17-19psi
Starboard temperature while cruising: 162F
Edit: One more symptom I see occasionally - After cruising for a bit and then going at slow speeds (docking or anchoring) I will see a little bit of steam come out of the rear port side of the boat.
With the temperature difference I'm pretty sure this isn't just a bad sensor, so what else could be the problem?
Ideas of cause:
Engines: Mercruiser 496 HO Seacore (w/ Axius)
Drives: Bravo III
Exhaust is captains call (not sure if that could matter)
I bought the boat last September and quickly realized this was a problem. I had a 1999 330 SS (w/ fresh water cooled 454s) before this and I figured it would be a simple fix like a bad impeller. After the battle of getting my pump out (those green and white flush hoses are too short!) I found the impeller was in great shape but there was some serious "swirl damage" to the housing which I learned is from sand/rocks getting stuck behind the impeller. To remedy this I bought a rebuild kit from http://www.marine-496pump.com. Unfortunately this still didn't solve the problem. Here's the symptoms I'm seeing:
Port water pressure: 4-5psi
Port temperature while cruising: starts around 162 and then slowly climbs to 167-175F
Starboard water pressure: 17-19psi
Starboard temperature while cruising: 162F
Edit: One more symptom I see occasionally - After cruising for a bit and then going at slow speeds (docking or anchoring) I will see a little bit of steam come out of the rear port side of the boat.
With the temperature difference I'm pretty sure this isn't just a bad sensor, so what else could be the problem?
Ideas of cause:
- Those green and white tubes don't have a good seal, the tube has come out of the metal end a few times while trying to install/remove pump, could this be allowing air in?
- Thermostat?
- Pump failing for other reasons?
- Something wrong with the Seacore heat exchanger?
- Intake clogged - the engines have both drive and hull intakes connected via a T connector just before the pump, even if one part was clogged the other should supply enough water (it doesn't seem to be clogged, water gushed in when I disconnected the pump!)
- Blockage in the cooling path after the pump - I may be wrong here but I would expect this to cause a higher than normal pressure, not lower, right?
- Water pump failure - This just pumps the coolant through the engine, not the fresh water, right?
Last edited by DracoDan; 06-15-2018 at 02:08 PM.
#3
Banned
iTrader: (9)
the 496 had the early version location for the water pressure sensor impeller housing area and then the later 496 had the water pressure sensor moved to the power steering cooler. Alot of times the pressure sensor can be bad or contamination filled the hole of the sensor as well
Last edited by BUP; 07-10-2018 at 12:04 PM.
#4
Registered
Take off a hose from thermo hsng to manifold. Same hose both engines.run engines and compare the water streams from each hose. If same size stream of water squirts just as far before it starts to curve down, the pressures are very close. Your reeadings of 5 and 20 should be a stream and a dribble.
#6
Gold Member
Gold Member
I am dealing with the SAME issue! Here is what I have found so far. I am using the same rebuild kit as you. I installed 2 kits and now my temperatures are running at 200 degrees. Those particular rebuild kits SUCK! The impeller is not stock and it is a lower durometer it is a lot softer. There is another rebuild kit that offers a plate for the bottom and a shim for the exit/flat plate part of the housing that allows you to use the stock impeller. I just ordered another brand and will update this as soon as I install.
#8
Banned
iTrader: (9)
I use the kit that is a OEM correct matched sized impeller and the correct sized SS plate that you drop in. The impeller is the correct sized because of the space the drop SS plate takes up, Impellers and housing are all about the correct tolerances for proper flow and cooling. If you need to know where to get them let me know.
#9
Registered
I am dealing with the SAME issue! Here is what I have found so far. I am using the same rebuild kit as you. I installed 2 kits and now my temperatures are running at 200 degrees. Those particular rebuild kits SUCK! The impeller is not stock and it is a lower durometer it is a lot softer. There is another rebuild kit that offers a plate for the bottom and a shim for the exit/flat plate part of the housing that allows you to use the stock impeller. I just ordered another brand and will update this as soon as I install.
Last edited by drumerjb; 06-04-2019 at 08:42 AM.
#10
Registered
I use the kit that is a OEM correct matched sized impeller and the correct sized SS plate that you drop in. The impeller is the correct sized because of the space the drop SS plate takes up, Impellers and housing are all about the correct tolerances for proper flow and cooling. If you need to know where to get them let me know.