New Heat Trouble

[screamineagle]

I have a pair of 502's bored and stroked to 540's with low compression and a conservative cam, running 850 Holleys with a crossover replacing the water pump. The crossover was on the boat when I got it as a 502. There were thermostats with 4 or 5 pretty good sized holes drilled around the outside edge. The motors never moved the temp gauge. After the rebuild to 540's at the end of last year and a lot of reading on here and the other site, I decided it would be a good idea to get a crossover with a bypass and try to regulate a little temp into the motors. I ran the end of last year and the first half of this year with no thermostats to keep the pressure down in the 540's. No heat on the temp gauges. This weekend I installed a beautiful set of Hardin Marine bypass crossovers. Painless install. Long weekend scratching my head/$$$! Both motors run at an indicated 130/135 with the 140 thermostats on plane. They both idle at 130/135 in neutral at the dock. The trouble I have is with the port motor idling in gear. It overheats when moving in gear. I can run it in neutral all day long with the starboard motor in gear and it's fine at 130, when I put it in gear, within a minute or two, the temp starts climbing. If I accelerate, it'll cool down or if I put it back in neutral at a high idle (1500 rpm's) it will cool down. First thing I did was to swap the thermostats, no fix. Next I replaced the raw water pump, still no fix.

I'm kinda stuck now. There are a couple of differences that I know of. First off, the starboard motor has a low water pickup and secondly it is about 5 or 6 pounds heavier on water pressure across the board. (15 lbs at 3k rpm versus 10 lbs on the port motor). There is no indicated pressure at idle on either motor but the pipes are dumping a pretty big amount

Any ideas what it could be ???

[Wobble]

i have 3 3/16th inch holes drilled in the flange of my t-stat. I am running the same crossover with the bypass hose and a sea strainer. this setup has been very stable for the past five years. I run the 160 stat though most prefer the 142*

[Airpacker]

sounds like the port raw awter pump impeller is coming apart.

[Ratickle]

sounds like the port raw awter pump impeller is coming apart.

What he said......

[Davidmnc]

What he said......

I'm with these guys

[Wobble]

been thinking about this, raw water pump impeller is the most likely as the others have suggested, second I would look for any obstruction in the raw water line from the engine back, such as old impeller pieces against the oil ps or fuel coolers, third I would remove drive and back-flush from the raw water pump through transom assembly.
make sure the oring on the mating surface between the drive and helmet is in place.

[MERPerformance]

I have a pair of 502's bored and stroked to 540's with low compression and a conservative cam, running 850 Holleys with a crossover replacing the water pump. The crossover was on the boat when I got it as a 502. There were thermostats with 4 or 5 pretty good sized holes drilled around the outside edge. The motors never moved the temp gauge. After the rebuild to 540's at the end of last year and a lot of reading on here and the other site, I decided it would be a good idea to get a crossover with a bypass and try to regulate a little temp into the motors. I ran the end of last year and the first half of this year with no thermostats to keep the pressure down in the 540's. No heat on the temp gauges. This weekend I installed a beautiful set of Hardin Marine bypass crossovers. Painless install. Long weekend scratching my head/$$$! Both motors run at an indicated 130/135 with the 140 thermostats on plane. They both idle at 130/135 in neutral at the dock. The trouble I have is with the port motor idling in gear. It overheats when moving in gear. I can run it in neutral all day long with the starboard motor in gear and it's fine at 130, when I put it in gear, within a minute or two, the temp starts climbing. If I accelerate, it'll cool down or if I put it back in neutral at a high idle (1500 rpm's) it will cool down. First thing I did was to swap the thermostats, no fix. Next I replaced the raw water pump, still no fix.

I'm kinda stuck now. There are a couple of differences that I know of. First off, the starboard motor has a low water pickup and secondly it is about 5 or 6 pounds heavier on water pressure across the board. (15 lbs at 3k rpm versus 10 lbs on the port motor). There is no indicated pressure at idle on either motor but the pipes are dumping a pretty big amount

Any ideas what it could be ???

Are you saying the stbd has a low water pick-up and the port is using the drive?

[screamineagle]

Wow, thanks for all the responses.

Air, Rat and Dave, I thought the same, the first thing I did was replace the entire pump. Housing,wear plate, and impeller. No change

This weekend I restricted the 1 inch hose between the crossover and the thermo housing with 4 hose clamps trying to force the water through th block at idle. It only succeeded in raising the water pressure in the port motor to about the same as the starboard. It still got hot idling in gear????

MER, the starboard drive has a handful of holes in the front of the nosecone as well as the normal pickups up higher on the sides and the port drive just has the ones in the sides.

Wobble, this weekend I back flushed the oil cooler and found 5 gallons of perfectly clean water. Nada in the oil cooler. I haven't looked back towards the drive.

The most disheartening advice I have had makes the most sense to me. Given the lower water pressure in the port motor, is it possible that I have a blown head gasket causing a loss of pressure?

This weekend I also went back to the crossovers with out bypass and no thermostats...next weekend will be time for a compression check...

[PatriYacht]

I have Imco lowers with the low pickup only. Once I got weedage that filled a lower and would not flush either forward or back. Took me an entire afternoon to get it to move to the point I was able to pull it out the lower with my fingers. You might want to drop the lower and see if there is anything blocking it. Good luck