blown

Ive been chasing oil and water temps since repowering with rebuilt carbed Hp500's a few years back.The engines came with the wrong non-bypass thermostat housings, I tried drilled stats but no good so put on a set of the standard HP500 housings. Couldn't really get those dialed in right, had low oil temps & milk under the valve covers.

My marine mechanic friend had a pair of the Sierra stainless steel housings, we swapped those in and it got rid of the milkshake (plus looked a lot better ) but the engines then ran hot, 255 oil temps pushing up to 260 sometimes. Water temp around 120. I change oil more frequently and have to watch gauges constantly & back off sometimes, kinda takes the fun out of things. Ran without T-stats for a couple summers but strangely it doesnt really make much difference for the water temps, though it takes a little longer (about 5 miles) to get them warmed up to running temps at the start of the day. Water pressure gauge doesnt even move without the stats in and barely registers anything with them in, but it just occurred to me that this may also have to do with relocating my sender from the bottom of the block (where its a b1!*# to get out to winterize, and often fouls with debris) to the port on thermostat housing (where its right next to the bypass).

Im not sure exactly whats going on, maybe these housings are bypassing too much water to my stainless marine manifolds? Reduced flow from older block and heads? Oil cooling should be sufficient as new stock oil coolers went on when I got the engines. I just ordered new AFR enforcers which will go on shortly. Also replacing intakes with CP's Xtreme machine Dart knockoffs which have the added rear water ports.

My mechanic bud is suggesting to switch to non-bypass crossovers (he has a pair lying around) without T-stats to lower oil temps but I dont want to end up with milk under the covers again. So im considering to use steward modified Robert shaw high flow thermostats and running dump lines from the rear intake water ports to the manifolds in order to relieve enough water pressure to avoid using the bypass. Does that make sense and would it be a good idea to add a pressure relief valve before the water dumps from the rear of the intake into the exhaust manifolds?

If the issue with my current setup is too much water bypassing the block, I could alternately keep it as is but add a pressure relief valve on each side of both engines, between the t-stat housing bypass ports and manifolds. But I do kinda like the idea of getting rid of the circulating pump and cleaning up the front of the engines.

Any flaws in my reasoning or advice on resolving this PITA?

smokediver

Milkshake as in just under the oil fill ? A good pcv system will clean that up. Wegner makes a really nice one . Running that to a catch can and than into a vacuum source will clean that up. You will run a little leaner at idle and may have to mess with your enrichment a bit . As far as oil temps , if you can run -12 lines and fittings to a properly sized oil cooler and filter pad you shouldn’t have any problems. I can’t really speak to your water temp .. I have been running closed cooling for several years as I am a predominately salt water boater.

SB

Explain ‘rebuilt’ . Everyone’s definitions seem to differ. Factory 500hp carb that’s jetted as from factory? Factory cam ? Factory exhaust ? ……….

250-260 is okay with an oil like mobil 1 15-50. Other good full synthetic 20w-50 /25w-50 / etc will be fine there too.

fbc25el

Do you have a oil cooler with a thermostat and is this a crossover system?

the deep

This is the setup I had on my HP, 15 years and never a problem boating in Pa. . Keith Eikert crossover and t-stat housing. No t-stat.

fbc25el

I prefer to use a by pass cross over system because when the thermostat is closed the exhaust gets very little water. It can also cause high water pressure. I would also use a oil thermostat.

fbc25el

blown

had a replacement 800cfm carb. I don't recall how they were jetted but we're going to set them up again from scratch once the new heads are on using factory specs as the baseline.
500 efi cam
stainless marine manifolds with the long risers mixing in water around 6 inches from the transom. on taking the heads off last month can see that im still getting reversion so planning to weld in 8 inch extension tubes to the inner jacket to make them almost dry to the tip exhaust.

Yes ive been told that 250-260 is doable but would feel a little more comfortable bringing it down some.

SB

The 250-260 max’s where derived from good conventional oils. Good synthetics okay to 280-300 and more. I wouldn’t want at 300 or more but many professionals say no big deal.

Okay, so it’s not a rebuilt 500hp, therefore OE tuning specs (carb jetting and etc) are thrown out if the window. Believe it or not, have helped a handful of people tune their motors and oil temp decreased at the same time. Tuned for power and drivability, the oil temps where a nice side result.

Do not set up ‘like’ factory carbs to factory jetting. If it’s not oe factory, it’s not oe factory. Most same cfm carbs do not have same fuel/air metering passages and restrictions snd boosters as each other.

So…..I’d get the tune to where you want it, get the water psi to, where you want it, and then see what you have to do to control oil temp.

blown

Currently not a crossover system. My marine mechanic friend wants to go to crossover, no bypass, no t-stat.
I had thought it had oil stats as my previous mechanic put new stock oil coolers and filter assembly on the motors when they arrived, but now im not sure and will verify. What am I looking for visually?