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Oil temp Problems?

S

srfdude

Member
Silverton 34C, heavy boat, needs all of big block torque.
I recently replaced the OEM engines from this '89 boat, with rebuilds from Promar.
A shout out to them, very happy with the results and the professional build. (Disclaimer: not affiliated in any way) I had originally planned on doing a valve job and related, but after tearing the top of one apart, I realized they were simply worn out. I had Promar install Comp Cams torquer cams, and replaced the OEM quadrajets/manifolds with Edelbrock 1409 marine carbs and Performer manifolds. Usually the BBCs come with 750 cfm Quads, these Edelbrocks are 600cfm. After talking to the folks there, their consensus was that 600 was more than enough to get to 5000rpm, more than I will ever run. This was a fortuitous decision, as the gas usage is significantly less than it was stock. According to my fuel sensors/Garmin network, I am burning gas at the rate of 1.3mpg at 3100 rpm, 20kts. Unless you are racing or need over 5000rpm, don't let anyone tell you need those gas gulping 750s. I'm showing usage of around 3mpg at trolling speed, 1200 rpm/6kts.
Now to the problem: I am using Amsoil 15-40 HD Syn. Diesel and Marine oil. Talked to the tech dept. there and this what they recommended. My water temps are rock steady at 180, both engines. Oil pressure 60lbs idle, 50 when warmed up. HOwever when I go to over 3000 to get somewhere, the oil pressure drops to 40 lbs one engine, 45 the other. This indicated to me the oil temps are higher than they should be. This is a closed cooling system, and I have a feeling the stock heat exchanger is inadequate. Any suggestions on a different/better oil cooler? Also some advice where would be a good place to install temp sensors on the BBC MKIV?
Thanks for any input.
 
good deal on your rebuilds.

Be advised that there's nothing wrong with the qjets.....when they are set up properly for the engines under them. They will only flow the air the engine needs and 750CFM is what they are rated for (at max pressure drop)....and most of them where never tuned to their applications.

You think the HX are inadequate....not the case as you state both engines are "steady at 180"....

Its not uncommon for the oil pressure to drop as the oil warms up...as long as the oil pressure stays high enough, its not worth worrying about. If you wanna change the oil cooler to something different, you'll have to do some custom metalwork or relocate the new stuff to a different location. I would hope both the oil coolers and the HX were (ideally) changed with the rebuilds (or boiled out and pressure checked at a minimum)....

If you want to probe the oil temps, the hoses going to the cooler are probably the easiest to access....
 
Hmm, I think I worded that wrong. You're right about the heat exchangers, the entire cooling system was changed to new. The oil coolers is what I was referring to, which also cool the transmission oil. I did have them tanked and pressure tested, and I think they are working per spec. I was never able to push the old engines enough to heat the oil, I think, so maybe as you say some pressure drop is normal. I was thinking of putting some automotive style air cooled coolers for the oil, but there is no air flow in the engine compartment and probably won't work. Maybe I could cobble up a fitting which has the sensor in the flow; have to think about that. I wonder what the racers do; oil temp is vital to those boys.
 
for a given setup, water will absorb much more heat than air....the U shaped oil coolers have been around for decades and, overall, provide satisfactory service. The other OEMs locate their coolers in different manners but size-wise, they are all close.

I'd suggest you look more at the trucking application than racing for 'ideas'....the load on a boat engine is pretty large and constant, relative to a car, and can last for hours.....
 
I may not be following your needs...... but Hayden offers a thermostatically controlled remote oil filter base that incorporates a temp sensor. The sensor controls a diverter valve that alters the oil flow to/from the oil cooler based on oil temp.


And yes.... Mark is correct..... liquids are much more efficient at heat transfer.



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