502 temp gauge and overheating issues.......help
 

Second time in the water since complete rebuild and am having overheating issues. Engine is a slighty worked Mercruiser 502 mpi bored to a 509 with isky cam, isky rollers, scorpion rockers, JE srp pistons, ecm tuned by Mark, adjustable fuel regulator set at 40 and Lightning headers with only break in time on engine before installing in boat.

While the boat is on the trailer and ear muffs on the drive the engine and temp gauge seem to run at normal temp. Gets up to 160 then drops down a bit as the thermostat opens and fluctuates with the rpm as normal. The gauge goes between 160-170 and with a laser thermometer pointed at the oil cooler to check oil temp it shows between 190-200 degrees after engine runs for a bit. Now the problem starts when I put her in the water and first thing that goes awry is the temp gauge. As soon as I start the engine and let it idle up to temp all looks good until I give the engine any throttle then it drops down to 100 degrees and does not move from that position til I turn the engine off and turn to key back to on position then it will read the current temp. I can do this over and over again and same results. When underway the gauge sticks on 100 and does not show me correct temp but using my laser temp tool on different parts of the engine I can see the water temp starting to creep up to 190-200 degrees. I am totally at a loss at would could be causing my problem because I have checked and confirmed all my grounds are under .5 ohm resistance, have replaced sea water pump impeller, back and forward flushed entire water path through engine and drive, checked thermostat in a cup of boiling water and oil pressure stays at 40psi steady. On the last test of the day yesterday I checked the oil temp at the oil filter and had risen to 230-235 degrees while the water temp had risen to 200.

Any ideas where I should start to look?

I have a full array of Livorsi gauges and am wondering if the factory mercruiser temp sensor is compatible with my gauge or do I need a new sensor? I have an oil temp gauge in my cluster but have never figured out where the sensor is for that one but am going to do research and get that gauge working.

It sounds like you have two distictly different problems here:
1. A water temp guage-sensor-connection issue.
2. A high water temp and oil temp operating temperature issue.

For the first obviously it might possibly be just as simple as a bad guage unless something was changed or the water temp sensor or connections were damaged during rebuild -removal-replacement, or wiring bad or damaged.

The second we seem to see a lot here on OSO Tech a lot after engine rebuilds and many times it has to do with mis-plumbing the remote oil cooler -oil filter or leaving out a oil by-pass valve in the rebuild process. What year is the 502 and was the oil filter cooler system modified or changed as part of the rebuild? This problem manifests itself it higher than normal oil temperatures that reult in the engine temperature climbing slowly above norms.

Best Regards,
Ray @ Raylar

Thanks Rylar for the response.

When I get home today I am going to take a look at the two oil lines coming out of the oil filter to the oil cooler. I know there is a hard stainless line that runs down the length of the valve cover and think that line goes to the inside port of the oil filter and the shorter flexible line which comes out of the center goes down to the cooler. Is that the correct path? Where is the oil by-pass valve and how would I know if it was left out?

I am wondering if not having the Mercathode connected yet would cause any issues with the gauges? I noticed a little pitting on a portion of the drive that had gotten nicked during installation and have heard that there can be some electric current produced due to the stainless and aluminum in the drive. The gauges seem to work perfect out of the water but as soon as I drop it in the water (which is salt) the gauges act up.

What is the good operating range of water and oil temp anyway?

Anyone know a good marine mechanic in the Jacksonville/St Augustine Florida area?

Just got home and looked at the plumbing of the oil lines into the filter, cooler and adapter plate towards the aft end of the engine. The small flexible line comes out of the oil filter in the center location and goes directly into the top port of the oil cooler. From the bottom end of the cooler and is another flexible line goes into the adapter plate port closest to the oil pan and then the outlet furthest from the oil pan that is a flexible line that changes to a stainless hard line goes into the outside port of the oil filter closest to the valve cover. Does that make sense?

As far as the oil bypass valve I am unsure about and have called up the guys that built the motor and they assured me it was built to spec and nothing was left out and that it must be something that I did. Great.

Z302:

The oil should leave the offset outlet on the block oil adaptor and run to the offset opening on the remote oil filter base. The oil then goes thru the filter and travels out the center outlet on the remote oil filter adaptor and routes to the oil cooler. The line out of the other end of the cooler then takes the oil to the center opening in the block oil adaptor where it returns to the pan thru an oil passage in the block behind the adaptor.

The pressure relief valve that we are speaking of is in the block fitler pad area offset from the center. This is there in case the filter clogs or a restriction in the lines or coolers build a pressure above 11 psi due to restrictions or blockage. At that point of restriction or blockage this valve will open and allow the oil to feed back to the engine for oil circulation for the engine and oil pump. If this small pressure relief valve is bad or left out the oil will not flow properly thru your remote oil filter or oil cooler and hecnce will return direct to the engine unfiltered and uncooled. This can slowly build heat in the engine because the oil is not being cooled properly and eventually this added heat can transfer to also start overloading the engines water cooling system since oil is not just for lubrication in an engine but is also responsible for a great deal of engine cooling.
We replace this small pressure relief valve with a 30psi GM vlave instead of the stock 11 psi unit that is a lot of GM engines to allow a little more pressure buildup in the system before the bypass opens and allow more oil to by pass thru the cooler and remote filter. We find this ensures a little more oil cooling in the remote system and lowers oil temps better especially in a higher performance build.
Some builders and shops completely plug this port to force all the oil thru the filter and cooler, but we don't recommend doing this with a stock size filter, line sizes and smaller oil ccoler as its difficult to always flow enough volume of oil thru the stock engine line sizes, fittings and cooler ports to feed the engine under all oil pump flowing conditions.
This practice of plugging this port I feel should be left for instllations of a larger capacity remote oil filter, larger oil feed lines and bigger cooler port and volume sizes.
I don't think this is something you did during the build as normally the shop doing the block work would be re-installing this bypass valve after they removed it to machine the block and then make sure all the oil passages were cleaned and cleared of any metal particles from machining. Some shops and builders leave this valve in during machining, we don't to make sure we get all the oil passages in the block free of any metal debris from machining and thats when we re-install the 30 psi replace ment valve. They are staked in place after installation.
You can easily remove your oil adaptor fitting from the block and with an inspection mirror you can view where this valve should be in place and make sure its there and hopefully in the closed postion.
If your oil pressure is low and even lower under use when warmer you should also make sure one of these pressure relief valves is not installed behind the center screw nipple in the center of the block pad where the adaptor center fitting pulls it up to the block. This is where the oil is returning to the block from the cooler and installing a valve here restricts the in block port passage down to about 3/8" in the center of the valve and will drop oil volume and flow from the filter and cooler and again add heat to the oil from reduced flow. This second valve should only be used in Gen 5-6 blocks where the oil passage ports on the pan rail in front of the block oil filter pad area are being used to route oil to the remote oil cooler or such as sometimes used in trucks and such. In your Mercruiser installation in a 1998-1999 502mpi this second valve is not used and should not be there.

As for water and oil temps I think you should see water temps between 160-175 degrees under almost all conditions and use based on your cooler water temps with a 160 degree thermostat. As for oil temps with your system and cooler size I suspect you should see oil temps when the engine is at operating temperatures above of about 190-220 degrees during most operating conditions. After long hard runs in higher temperatures its not uncommon for temps to go slightly above these with water temps maybe seeing 175-180 and oil temps getting to 230-240 , but these should drop very quickly when you pull back to cruise rpms or idle rpms if you cooling systems for both water and oil are properly sized and are working properly.

As for your Mercathode system non-connection and galvanic action causing your guages to go erradic, I have never heard of that, but I am not an expert on that so maybe someone else some expierence with that possibility. I thin I would just look for connection or guage issues unless someone can confirm this is a possibility.

Best Regards,
Ray @ Raylar

Thanks Ray,
As allways, a great information, for all of us,never stops worry about oil by-pass valves - routing
Bjorn.

(Not my intention to brake in to your post Z302)

I have 502 crate engines that had oil issues also, to the point that one of them had to be rebuilt because of lack of oil to the mains.. So I decided to remove the center valve and plug the outer one, hoping this would solve my high oil temp issues.. Well with 140 t-stats my water temp ran about 160 and my oil temps climbed well above 250* on the hose...

Is it possible that there isnt enough water going thru the system by being on the hose for the oil temps to be so high?

We did install crane 731 cams in the engines, also installed huge oil coolers and a teague block adapter, I should add that I used the stock remote filter adapter and the stock oil lines from a 454 mag on the 502.. Is it possible that the oil lines are restricting the flow of oil and slowing it down as it travels through the system?

I do have another question! I have dry exhaust if there isnt enough water flow thru the cooling system of the block and oil cooler could that cause the high oil temps? Basically I guess I'm asking if I'm not dumping enough water from the cooling system would it cause the oil temps to be higher than if I was using say stock mercruiser exhaust?

I finally found time this week to work on my engine and it's overheating issue. After replacing sea water impeller and housing and still having the same issue I decided to remove all hoses and coolers to visually inspect for any blockages. I did find a could pieces of the impeller in the oil cooler but they were really small and would not of caused any real blockage of the water flow. I did not find any other restrictions anywhere in the other coolers and or hoses and decided to take off the circulating pump to flush out the block and see if any thing was lodged in there that would cause an issue. Bam! Found the issue as soon as I removed the circ pump as it rattled like a baby rattle. Took apart the backing plate and found the impeller broken in to two pieces. Problem is hopefully solved and will find out as soon as I pick up my parts from KE in Palm Coast (nice to have a performance boat parts warehouse only 20 minutes away).

Thank you all for the support and advice.

I'd pitch the circ pump and get a crossover kit with the bypass from KE instead, one less part to fail.

Well the new pump is on and she is finally running like she should. I bought a really nice quality water pump from the guys at Hardin Marine(Hardin Marine, KE and CP Performance I think are all one company now) in Palm Coast for just over 100 bucks as well as a high flow 160 degree thermostat. Ran the engine for almost 45 minutes and never got over 125 so now hopefully when she is under load I am going to be right where I need to be. Used my old igloo marine cooler to draw water from to make sure all cooling components are working correctly.

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