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HP 500 Low oil pressure, low water pressure, low engine temperature

Old 08-07-2021, 11:50 AM
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Default HP 500 Low oil pressure, low water pressure, low engine temperature

Thanks for the help on my other problems OSO.

So I have now had this engine in and running for about a month now. The lake has only allowed me to open her up 1 time so far. It really is much more stout than the 502 MAG I previously had. But I do have issues i cannot figure out still.

1. low oil pressure.

Using Torco 20W 50 motor oil. I get 40 psi at the gauges (new gauges this winter) at start up.(The engine came with Merc 25W 40 in it and had same pressure before I changed it out) After any moderate running 3k RPM for extended periods and I drop down to idle speed, pressure drops to around 20 PSI. I have read this is normal for hot oil.

I finally made a brief, fully loaded (7 adults) WOT pass up to 5k RPM I saw oil pressure was only at 38 psi. So pressure is actually decreasing with more RPM.

I am going to try removing 1 qt of oil and see if this helps. Being a new to me engine, and the dip stick doesn't appear to be the original, I am suspect at the amount of oil I should have in the crankcase.

Can anyone please measure the length of their HP 500 dipstick so I can compare mine? Mine has the yellow plastic ball on top, the original appears to be the metal "p" handle type.

2. Low water pressure

Only seeing 3- 4-5 water psi max at cruising speed. Didn't observe pressure at 5k RPM.

New water pressure gauge installed this winter. Fitting installed into thermostat housing. Long run of hydraulic hose going from front of engine along the side up to the gauges. Prob about 25' of hose total. Not sure if I am getting pressure drop due to length?

Seawater pump was new with the engine. I also replaced it to eliminate possibility. Water circulation pump was just replaced. Thermostat housing has been changed from stock. (came like this when I bought it)


3. Low engine temperature

New temp sender (and old one tested too) mounted in intake manifold. When in the water gauge almost never comes off the peg. (New gauges this winter) When running on the muffs in the driveway, it will go up to 175* and the thermostat opens and it will drop down to around 140*. After driving to destination and restarting the engine the gauge will display temp due to heat soak. (maybe 130-140ish?) but once under way, it will fall back down to below 120*

I was chasing my tail thinking the gauge was not working, but it appears it actually is, just not reaching enough temp to register.

Not sure if these are related in some way or not? Possibly too much flow and not enough restriction?

Water route is as follows. Bravo 1 to sea water pump. sea water pump to oil cooler. Oil cooler to power steering cooler. Power steering cooler to thermostat housing front port side fitting.

There is no bypass hose being used.

Rear port and starboard thermostat housing fittings go to bottom of CMI headers.

There is no milky color to oil, so it does not appear to be condensating. Which means oil is getting up to temp

Here's a pic to show what I have installed. As always, thank you for your help.





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Eddienel (08-08-2021)
Old 08-07-2021, 01:00 PM
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Man...your trials and tribulations with this project have made me totally rethink doing something similar!

Not being familiar with this engine at all, but it seems to me that the most perplexing issue is the low temperature whilst running.
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Old 08-07-2021, 01:14 PM
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First off what size is the oil pan ? how many qrt's did you put in including the filter ? your oil pressure doesn't look out of line to me, at higher rpm's some times the oil will start to foam with the crank wiping it, does it start to come back up when at idle for a few minutes, water temp looks ok to, whats the water temp you are running in. is the temp sender unshrouded meaning in direct water flow, might need a new T-stat
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Old 08-07-2021, 08:45 PM
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Originally Posted by bajaman View Post
Man...your trials and tribulations with this project have made me totally rethink doing something similar!

Not being familiar with this engine at all, but it seems to me that the most perplexing issue is the low temperature whilst running.
Don't sweat it, it's just par for the course when you buy someone else's problem.

Many of the electrical issues are of my own doing. I replaced all my gauges and redid the dash panels, so EVERY wire was removed and replaced.
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Old 08-07-2021, 08:56 PM
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Originally Posted by F-2 Speedy View Post
First off what size is the oil pan ? how many qrt's did you put in including the filter ? your oil pressure doesn't look out of line to me, at higher rpm's some times the oil will start to foam with the crank wiping it, does it start to come back up when at idle for a few minutes, water temp looks ok to, whats the water temp you are running in. is the temp sender unshrouded meaning in direct water flow, might need a new T-stat
I believe it's an 8 qt oil pan. I put in about 8 1/2 - 9 qts when I changed it. K&N tall oil filter

Rule of thumb is 10 psi of oil for every 1k RPM. So by that, I should see 50 psi at 5 k, correct? Honestly, I haven't noticed how long it takes for it to come back up from 20 to 40 PSI as I'm usually back in the marina/dock and shutting the engine down.

Water temp I'm running in is around 75* now.

Temp sender is mounted inside a thread adapter in the intake manifold. It does appear the sender is recessed in the thread adapter. Maybe There's an air pocket trapped beneath the sender and not actually immersed in the water?

Thanks for the help F2.
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Old 08-07-2021, 09:18 PM
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Originally Posted by xlint89 View Post
I believe it's an 8 qt oil pan. I put in about 8 1/2 - 9 qts when I changed it. K&N tall oil filter

Rule of thumb is 10 psi of oil for every 1k RPM. So by that, I should see 50 psi at 5 k, correct? Honestly, I haven't noticed how long it takes for it to come back up from 20 to 40 PSI as I'm usually back in the marina/dock and shutting the engine down.

Water temp I'm running in is around 75* now.

Temp sender is mounted inside a thread adapter in the intake manifold. It does appear the sender is recessed in the thread adapter. Maybe There's an air pocket trapped beneath the sender and not actually immersed in the water?

Thanks for the help F2.
the 10psi per 1k is an old wives tale…

our 500efis’s when hot are 20psi at idle and 40-45 psi when running regardless of rpm.

has always been that way on both motors…never had a problem. also depends on oil pump and spring.

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Old 08-07-2021, 09:47 PM
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Where’s the oil cooler? A 500hp motor needs a pretty large one. If you are running a 502 Mag style cooler, it’s not enough. I am pretty sure when oil gets too hot, the pressure drops.
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Old 08-08-2021, 08:55 AM
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Originally Posted by 1MOSES1 View Post
the 10psi per 1k is an old wives tale…

our 500efis’s when hot are 20psi at idle and 40-45 psi when running regardless of rpm.

has always been that way on both motors…never had a problem. also depends on oil pump and spring.
Thank you for that. Good to know

Originally Posted by liquidlounge View Post
Where’s the oil cooler? A 500hp motor needs a pretty large one. If you are running a 502 Mag style cooler, it’s not enough. I am pretty sure when oil gets too hot, the pressure drops.
Not running the 502 MAG cooler. Using the OEM HP 500 cooler that's the entire width of the engine at the back. Pretty big. Thank you

Looking through the service manual it does address my oil pressure and only lists 30-70 psi at 2k RPM. So I guess I'm good.

Shows it being an 8 qt system with filter. I originally added until the dipstick was on full mark. Yesterday I did remove about 1 qt for testing. but water was too rough for anything above 3k RPM, so today hopefully I can see if that helped bring it up a bit.

Thanks for the help
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Old 08-08-2021, 09:11 AM
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btw, nice looking mill, my ocd needs you to paint the lifting ram............
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Old 08-08-2021, 09:28 AM
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It IS a beautiful engine...sigh.
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