Raw water temp to engine temp

[mattyboy]

how much does raw water temp play in engine running temps?

last year the boat ran at about 170 then would spike to 200 or so after a hard run then after a minute at idle come back down to 170-175 this year the boat seems to run 180-185 at idle and spike to 200-210 after a hard run. the lake is warmer this year water temps mid to high 70s .

it is a HM crossover raw water crank pump not stat

will see if i can borrow an infrared gun and check the motor for hot spots

thoughts before I tear into the cooling system

[mike o]

Where's the pickup, could you be sucking air having fun with boat wakes on a busy weekend? Any time I have seen spikes like that is when some thing might be plugged up a little. Friday nite we a few pops while cleaning a 283 Chris Craft block pulled from a 61 wood Century Coronado that had a noise in it. Got 2 coffee cups of rust out of the water jackets and manifolds. Wonder if something in your motor has moved around and caused a small restriction some where.

[mattyboy]

the pickup is in the drive the pump is on the front of the motor the water is gravity fed up thru the drive thru the goose neck then sucked from there.

the impellor and motor are two seasons old the risers are not.

I did have a riser exit plugged last year started burning the hose but even with that the gauge didn't move much that was lake george much colder water

the port side does dump a bit more water than the starboard but I thought that was kind of normal like why they take your blood pressure on the right arm

[mike o]

Ya, I remember, THIS motor had one hot manifold and other plumbing stuff going on from sitting 3-4 yrs. But it did take out the head gasket causing steam in a cylinder. Should be able to put your hand on the flex exhaust hose. Or, water coming out of the pipe briefly without getting scaled. I had a 351 w for yrs and both side should pretty even. Sold the boat with 1800 hrs. ADDED. The boat was a 79 ski nautique. once in a while hot rodding around the temp that would normally run 160 would spike to 200. The pick up was under the boat. and the transmission cooler would have weed in it causing a blockage. So, it could be something simple like that 2 :crossfing:

[Ghost]

I may be answering something you weren't asking, but the spikes sound pretty normal to me, meaning I've observed that spike on multiple engines that seemed otherwise fine.

My belief is the spikes are due to LATENT heat buildup in the engine during the hard run. While running hard, a lot more heat is produced and the internal temps are higher than at idle, but there's a lot more cooling water going through the system, such that the RATE of wicking away BTUs is much faster than it is down at idle. The temp sensor only sees temp at one spot though, so we have a tendency to think about only that one. That measured temp might be close to the same at warmed-up idle ands during the hard run, even though the cylinder walls would be much hotter during the hard run.

The upshot is that when you back down from the hard run, your cooling flow drops way down. But there's still a lot of heat built up further in the engine that is making its way out to the "edges" so to speak. Because the relative trickle of cooling flow can't haul heat away as fast, the temp where the sensor sits rises for about a minute or two, until the smaller cooling flow takes care of the backlog.

That addresses the spike part (if that was even part of what you were asking :) ), but not the difference in absolute temp at steady state. That sounds like it COULD be related strictly to raw water temp, depending on our system, but I'd have my eye closely on it, recording measurements at different spots, in case something else was involved, restricting flow. I'd bet it's more than just the lake temp. The ten degree difference seems like a lot to me. How much warmer is the lake than normal?

[joseph m. hahnl]

With out a Tstat it uses a restrictor? Your question is actually about the ambient temperature. I think it could be possible that it could effect it some. If you run it on a cold water hose at idle and it still goes to 180, you might want to check for air leaks first. I check the heat of the water coming out of the pipes with my hand. If it is hot and not loop warm you have a problem with heat exchange. In mine with the head gasket blown the exhaust gas was escaping into the water passage super heating the coolant and in turn the cold water at the exchanger couldn't keep up. The water coming out of the pipes was razor hot:eek:

[mattyboy]

no restrictor this is a Holman Moody crossover system pumped into each side of the block by the timing chain cover then out of the intake then into each riser. the sender is at the exit of the intake no heat exchanger or bypasses to the risers

on the hose at idle it doesn't get to 140 or so but I don't go above idle rpms may be 1000-1500 for short periods


every HM setup I have seen spikes a little after a hard run then comes back down

the numbers on mine just seem to be 10 degrees or so warmer this year?

[MOP]

Matty you may have better results with a Tstat, when I was racing Ford 60's they would run quite a bit hotter without restricters. Note all raw cooled engines spike when coming off a run, the water slows way down allowing the hottest water to rise giving a false reading. I had to demonstrate this to quite a few customers, they would come in with a new boat freaking out about it over heating. It is possible that the cross over is allowing the water to run through the block to fast, if so it may not pull out the same BTU's as regulated water.

[mattyboy]

I would think if the water temp is going up that water is slowing down in the system allowing the water to stay longer taking more heat out of the block??

[Morgan's Cloud]

I haven't seen an engine that doesn't show some sort of spiking after a hard run regardless of its cooling system type .
I know that in my case , no matter how hard I've run , I always anticipate in advance where I'm going to need to really slow down and do it well before that point. A moderate slow/fast idle period before 'stopping' avoids the spike from residual heat soak down.

Otherwise , there's only one way to put this to bed .
Find a cooler lake and test it out there . But you're already on the 'queen of lakes' !

[gcarter]

I haven't seen an engine that doesn't show some sort of spiking after a hard run regardless of its cooling system type .
I know that in my case , no matter how hard I've run , I always anticipate in advance where I'm going to need to really slow down and do it well before that point. A moderate slow/fast idle period before 'stopping' avoids the spike from residual heat soak down.

Otherwise , there's only one way to put this to bed .
Find a cooler lake and test it out there . But you're already on the 'queen of lakes' !

Steve, the Minx (and the TR also) had/have electric circ pumps and do not spike regardless what you do. Of course, under full throttle, the temp does climb, but when the throttle is chopped, the temp will work its way down slowly until it reaches normal temperature. The system runs at a steady 55 GPM.

[mattyboy]

My lake is 10-15 degrees warmer than lake George so I figure I will send the toon boats out ahead of me and dump a trail of ice that should do it

[mattyboy]

did some testing yesterday ran her on the hose for a half hr temp never went above 150 or so. I have a flush valve installed so now I am wondering if I have some kind of blockage coming from the drive.

[maddad]

Matty, the AQ water tube through the drive has a few O-ring seals that go bad. At speed they're out of the water and let the crank driven pump draw air into the loop spiking the temps, at idle the seals are back in the water where it doesn't matter if they're bad. Check the seals, and do yourself a favor, consider getting your water through the hull.

[mattyboy]

Maddad I forgot about those my 16 had a thru hull pickup any easy way to test those seals?

[mattyboy]

Looks like I had two issues one

A. I rerouted the water intake hose alongside the stringer and up to the pump this season. Instead of it running along the bottom of the hull That was my 10 degree difference
B. it is running hotter on plane then off plane 170 off plane and 200 on plane so it looks like the seals in the drive are bad