Dart Block Oil Temps
 

Here's a scenario I'd like to pose on behalf of a friend to see what we can come up with as a possible or probable cause and suggested solution(s):

Dart Tall Deck 632" block when assembled, runs high oil temps (easy 280 and rising). Oil temp goes up quick and continues to rise. Oil is Full Synth 25W/50, raw water cooled (no strainer but clean) with a 3" x 24" combo oil/ps cooler (Hardin I think). Engine oil temp sender located in pan, matched to Livorsi gauge. On tear down, bearings show no discolorations or burns/blueing. All clearances were checked and apparantly correct prior to assembly - Crank ground 0.010" and polished. I believe the motor runs the standard Melling M77 oil pump.

The key issue is that this is one of two engines in the boat, the other engine is the exact same and has no problems with oil temps. Water temps for both engines are the same, as is pressure. The oil cooler on the other motor is the non combo cooler but is slightly smaller (about 20"). Everything is identical between the motors, cooling, pumps, ancilliaries, carbs, jets, set ups etc.

Could some small blockage somewhere cause this temp prob? It's a new block so where could the problem be? Casting error?

All other simple checks and tests have been done. My thoughts were bearing clearances. All oil lines are AN-12, the filter is the HP6 (like KN 3002) on Canton adaptor with the big fittings.

The pan feels hotter than the other motor so I don't think it's just sender location in a hot spot on the pan.

Could it be that the oil pump is not sufficient? I haven't confirmed that the other motor is in fact running the M77 as well but I was told they were built identical so I am assuming it is?

The key issue is that the other motor is identical but perfect and never gets the temp above anywhere but optimum (240 - 270). The other motor has a smaller cooler but apart from that, it is the same and has never had any problems.

Any suggestions or other things to check would be greatly appreciated. The motor is out of the boat at the moment and we want to get it right before it goes back in!

Thanks in advance for any help or advice.

John

Friction of course causes the heat. Sounds like theres some clearance issues somewhere in the engine. I would pull the caps from the bearings rods and mains and take a look to see how wear is doing. Could also be a piston fit issue. Just my 2cts worth.

Check for a missing or stuck open oil pressure release valves in the block at the oil filter flange and such. On some blocks if these are misssing or bad the oil will completely bypass the cooler circut depending on how its plumbed.
could be the problem.

Best Regards,
Ray @ Raylar

Just a thought here. How about if the O ring that goes between the rear main cap and the block was left out. That may cause a flow problem, creating the high temps.
I have strayed away from the standard M77 style pumps. Now, I strickly use M10778 pumps.

Thanks for the input lads!

I've confirmed that the filter pad bypass has been either blocked off or came blocked off. We checked the bearings and they showed no abnormal signs of ware (no discoloration or uneven polishing).

I'm curious to know more about that rear main cap O-Ring, is that specific to a Mk IV engine? or is that on all motors? How easy is it to 'Forget' to put in or replace?

I avoid the M77 pumps too, but I run the 10778C just in case. I think that may be a required upgrade on the cards already but if both motors are already running the same pump and the other one is alright, I'm at a loss as to this cause!

Thanks again so far!

John

With a temp gun shooting at the hose fittings to the oil cooler, do you see hot on one side and cold on the other? Have to be close to the fitting to get a good reading, but you should see a difference.
Can you run the motor on the hose and see high oil temps, or did you, should I say.
I left the oring out on the main cap for a couple of motors, till Vinny mentioned it. And I didnt have high temps because of it. I did have an oil thermostat (KE) and it didnt work.. made oil hotter.
Are you getting good water flow through the drive and pump and oil cooler? Any diff in the water temp on the two motors?
Just kind of tossing thoughts out..
Comes down to oil flow and water flow through the cooler. It should cool it down if it has enough oil and water flowing through it.
Is the oil flow against the water flow on both motors?
Good luck with it.. and keep us posted.
Dick

Thanks Dick, we'll give the temp gun a go when the motor's back in. The flow through the drive is fine, the 4 slot low water pick ups in the sportmaster lowers give plenty and now we need to manage water pressure with a valve but the other motor is plumbed the exact same way with a smaller cooler with the same flow. Water temps, oil pressures and all other checks are the same and are perfect, it's just the oil temp on this one motor that has us stumped! There may be an issue about not getting enough water out of the block through the exhaust due to the size of the outlets on the tailpipes (dry exhaust with custom tails with built in dumps). Could the restriction of flow cause the high water pressure which was relieved with the dump valve but is now causing a hot spot in one of the engines maybe? (That's a mouthfull I know!)

Thanks again,
John

What about swapping out the oil coolers & run the other motor on the hose. Would be an easy test to rule out any issues w/ the coolers.

Another cause of high oil temps is lean fuel mixture. Make sure the fuel system is providing the same amount of fuel to each engine. Alittle bit of detonation will heat the oil fast. Make sure both engines have the same amount of ignition timing and maybe back both off a little. 34 total is usually safe for standard style heads.

While I doubt this is your problem, here is a link that shows the #5 main cap O ring... Check out part 18
I am going with a flow problem, either oil or cooling water.

http://www.mercruiserparts.com/Show_...onnecting+Rods

What about retarded timing.. that will cause heat also..
The restriction in the tail pipes may be an issue. Like you say.. not enough water going through the pipes to cool the motor.. but you should see higher water temps also. What water temps are you seeing?

Hi Dick.It's Carl and it's my boat John's refering too.Water temps are the same between both motors,140 thermostats.oil pressures are identical just the port motor gets hot.Driving me nuts.
Actually put 2 18 x 3 coolers inline and it made no difference.Oil is hot going in to the cooler and cold going out.
Starboard will read say 190 and the port is already at 250.
If there was a restriction in the exhaust water dumps i feel i should be seeing high water temps.
There is no bypasses in Dart blocks correct?

It is almost as if oil is bypassing the cooler.Maybe not all of it is bypassing but if thats the case i should see it in the oil pressure shouldn't i?

Is there anyway oil can bypass the filter pad in a Dart Big M Block?

Carl
I had the same problem with a KE oil thermostat. Not all the oil was going thru the cooler.. and it would get hot.
I don't believe there is any spot for the oil to bypass, unless some passage got drilled to deep and hit a passage on the input side of the motor.
When I put mine together I had no concerns of a bypass, like is in the GM gen V motor.
I did a test once when I had oil psi concerns. I put a ball valve inline with the oil filter and put a gauge on the output side of the motor. When I shut the valve for a second or two, I could see the oil psi jump up to 80psi or so. What ever the bypass was set at. I had suspected a problem with the bypass. But it seemed to work fine.
My point being that at an idle I was able to shut down the flow of the oil and check psi, without hurting anything. IF you do have some internal leak that is causing a bypass, maybe the ball valve test would show it. If psi jumped to something less than the bypass valve settng it could show an internal leak of some sort??
Maybe if you swap motors side to side.. the water maybe colder on that side of the boat??? Sorry couldnt resist.. :(
This is a tough one.. but think basics and you will find it. It took me three years to find the oil thermostat problem with mine. Finally just bypassed it and bingo.. problem solved. Keep at it, you will find it.
Dick

try taking the oil line that comes from the block off and spin the engine over(not starting) with it in a clean container, ck the oil flow and volume....crank over for a timed amount..measure the oil amount, then ck the good engine, that will tell you if you have a problem inside the oil passages in the block....good luck Rob

Thanks Rob, Dick and everyone for your thoughts. :drink:

Lots to check but the motor's out at the moment and we'd like to confirm the possible physical issues prior to reinstalling it.

So the Dart M Block has no bypass valve and no tube or hole for the valve to go in? The motor doesn't run an oil thermostat so at least that can't go wrong!

Would you be able to generate sufficient oil pressure with a drill and oil pump primer while the engine is still out of the boat to acurately check for any internal flow discrepancies?

Cheers,
John

Not according to Dart. I also have a 10.2 dart block, 640 ci engine. I had the same problem. I literally pulled my hair out trying to figure it out. I did the same things that you are doing only to find out my sending unit was bad. I ran the boat and the gauge shows 300 degrees but when I used an infrared pyrometer on the pan and before the cooler on the fittings the temp was 220 degrees. now I realize that the oil is going to be a little hotter than the fitting but not 80 degrees. Also I checked the temp at the remote filter which I had plumbed before the cooler but have since changed that and it was also 220 degrees. I also changed the location of the sender. I know everyone says it needs to be in the pan but that doesn't make much sense to me since the oil in the pan is going to be hotter as it just went through the motor? I want to know that my cooler is working so I put my new sender after the cooler. This may or may not be your problem but I thought I would throw it out there. I also tried the jetting changes but it didnt make any differnce as I knew from reading my plugs that my motor wasnt running lean but I was willing to try anything lol!!! Good luck to you and I am sure with a little trial and error you will figure it out.

I just looked at the pic. Read over your issue. First of all, the water crossover and thermostat housing, who is it from? If you have tested the incoming water to be free of air we are good to proceed from there. I don't want to just jump on this with both feet until I know certain things.
Was there any issues with oil temps before?
Do you have a 140 thermostat or restrictor plate?
If you have a thermostat, what size bleed holes, how many?
Have you shot a temp gun on the cylinder heads, like all 4 corners where the water would enter the manifold?
How fast are the temps coming up, what RPMs, time.
I have seen about 20-30 degrees between coolers that are dual and single and also a pressure difference.
If you have to test again, read your temps with a gun with someone in the engine compartment if possible.
I advise you not to run this boat up again until,these questions are addressed. This may be the same problem I had with a 38' Top Gun that I built some 800 HP for. If it is, It will be a easy fix for you, that was a big head ach and alot of $$$$ for me.
Mark

he also said he touched the oil pan with his gauge showing 280 and rising and if the gauge was correct I dont believe you would be touching an oil pan with filled with 280 degree oil long enough to tell a difference between the two pans? I may be waaaaay off here but its worth a shot. swap the senders and see what happens.

This is sort of messy and everything seems to contradict itself.
I have 140 thermostats with 2 1/8 holes.
Can't remember where the crossovers came from.
Temps come up extremely quick,5 minutes @ 4500 and the port is rocketing up.
It's like it is running with no cooler.
Forget what temp i touched the pans at.I know that the port is definetly much hotter than starboard.Whether i grab the pan,remote filter head fiting,cooler lines it doesn't matter.
Can anyone tell me,the port above the filter pad on the dart big m.What oil runs there.It has a removeable plug.
In the first race i actually read oil temp from this port due to the motor coming over with the wrong pan.
It now has the correct pan and the sensor is now in the pan.
First race oil temp was fine @ 220.

If high oil temps are caused by a water flow issue would'nt the water temp also be up?
Water temp is fine never over 140.
Because we where so rushed to get the boat ready for the second race realising we had oil temp problems and still sorting out all the other little issues that come with a new boat,i actually put another 3 x 18 cooler inline with the existing the night before we had to travel.
Made no difference.Oil in was hot,return to the motor was cold.
So now i'm at,motor out,bearings fine.All looks good.I need to check oil galleries somehow.
If the oil was restricted in the block to the filter pad would'nt the pump relief open and i would never know there was an issue.
So a slight restriction in the gallery that goes from the oil pump to the filter pad.Low flow of oil through the remote lines and cooler/filter,oil pump relief opens because of the pressure caused by the restriction.Could this be it?
Oil pressure is the same in both.Slightly lower when the temp gets up.

Carl,
I recently primed my motor with a gauge on it, the port above the fiter pad on back of the block. With a Milwaukee drill set to 1200rpm, I saw 82psi at the back of the block. That was with the remote filter adapter with a bypass hose on it. So yes, you can get enough psi to test. It would be good to know how much psi each motor makes with the same drill, and setup.
If you are bypassing oil into the pan it will get hotter, cause not all of it is going thru the cooler.
When I had my thermostat problem, I would see 270-280* after the cooler. If you see cool temps after the cooler, how much heat is it taking out? If it is cooling properly the oil that is going thru it, but the pan still gets too hot, I would suspect a restriction and oil going thru the bypass on the pump. That restriction would be after what ever point you are checking the psi..
Are you running the same lifters in each motor.. They could be restricting the oil flow if they are not correct.
Keep looking..
I pulled a pan on one motor and ran the oil pump with a drill using a coffee can of oil to the pump. Found my leak.. the professional motor builder put standard bearings on a .010" under crank and never measured it.
If you have to, pull the pan and rotate the motor with the starter, and supply oil to the pump, what ever way you can.. then watch psi and flow.. if it is coming out of the pump bypass you should see..

Hope that helps.. Keep at Carl, you will find it.
Dick

Yes, you can use a primer and a drill to test, just have to do the same for the "good" engine to compair to....

The reason I ask all those questions, I had a problem like yours or it seems the same. It drove me insane. I don't want to say this is the problem, but try this.
Cap the by-pass. Remove the thermostat. Make a restrictor plate from sheet metal with a 5/8 hole in it or gut the thermostat. Run the boat, you need to check the engine temps with a temp gun first and during the test with the changes. The water temp is not going up because, the water around the sender is cool, what happends is the water at cylinders 5&7 get hot because of the flow around those areas, plus 5&7 fire in sequence, steam pocket produced, which causes the oil on the head to get super heated. You'll know the valve cover will be hot as H-ll there!
What happens if this is the case, the water coming from the by-pass sprays on the top of the thermostat and confuses it on opening, this all seems to effect the odd # bank. I moved the by-pass hose to the center of the intake and sent that warm water to the top of the thermostat housing. Take the front of the intake below the thermostat drill and tap it to 1/2 npt, use a #10 AN and your finished. Just cap or plug the cross-over or read your water pressure at that point.
From now on I use nothing but, the cast thermostat housings from Stainless Marine, they have a built in diverter to prevent this issue. I have used Stainless in the past with no problems, I used Eddie Marines, this was the problem. I called them about it once I knew the problem, their anwser was to drill holes until the issue went away. 800 HP heat doesn't go away with drilling holes in a thermostat! If this is the problem this is the answer to correct it. Or buy a housing from Stainless Marine, this goes for both engines if so the case. Let me know your test results. Mark