How do know if need to replace a thermostat?

Motor has been running 10-14 degrees hot and going to clean heat exch, ucoolers, etc. Wondering if should also change out t-stat? No idea how old it is.

If you get steam out the exhaust, I'd up the raw water flow. If the coolant temp is high, even at idle, I'd replace the thermostat. Of course, there is that chance its stuck at some setting where its ok at idle and runs hot at cruise. I'm just saying that chance is less than the other "unknown" stuff in your raw water side. But, its a fairly easy job, your call.

Is the right temp for the coolant measured at the thermostat housing and should be around 165-170? I measured ysterday at cruise and one side was about 168 and this side which showed running about 183 at guage measured about 180-188 at t-stat housing. What does this indicate? Trying to figure out what is causing overheat.

How would determine if raw water or coolant side is causing to be too hot? And how bad is the 183 temp? Other side runs about 170.

rmm said:

How would determine if raw water or coolant side is causing to be too hot? And how bad is the 183 temp? Other side runs about 170.

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You are about 15 degrees hot. Again, is there steam out the exhaust? Either when cruising or when throttled back after a high speed run? That drives my decision on what to do.

These motors have always steamed some, maybe a trail 3-5 feet back, have niticed the hot motor steaming slightly more, haven't noticed more steam when slowing or back off plane after run. Andbasically none at idle.

I have the exact same issue. One motor idles at 160 and cruises at 165; the other idles at 160 and shoots up to 180-183 at cruise. So far, here's what I've done.

1) New raw water impeller. Old impeller had one partially torn vane. Pump looked fine. No change in cruise temp. after impeller replacement.

2) New risers and elbows. Now cruises at 178-180; 160 at idle. Small improvement but nothing to speak of.

3) Inspected raw water strainer and intake feed to raw water pump. All clear, strainer lid sealed. Water rushes in from intake feed like there is no tomorrow.

4) Disconnected raw water inlet and outlet hoses from u-cooler. Back flushed u-cooler using 80 psi dock pressure. Water rushed right through cooler. A few tiny pebbles came out. No obstruction apparent.

5) Removed and had heat exhanger prof. cleaned and pressure tested. (This was last year).

6) Visually inspected raw water flow at idle. Appears about the same on both sides. Good flow. Steam is similar on both sides at cruise, at least from the bridge there are no major differences.

Still have nearly 20 degree temp rise at cruise on the affected engine. (And I cruise in 65 degree sea water).

I was about to try a new u-cooler but after it passed the above test it is doubtful a new one would make any difference. Could also be an inefficient heat exhanger, but that's an expensive guess. Maybe there is a way to meaured the delta T of the raw water at cruise before its injected into the exhaust; that might tell you something about heat exchanger efficiency. Would have to use the other side as a control...

I guess I'll replace both 160F t-stats with 180F t-stats. From there no temp. rise will be apparent. Not much of a fix, though, unless the t-stat on the affected side only opens part way.

major_tom said:

1) Pump looked fine.

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This means the graphite bushing in the cover is not oblong, there are no deep scores in the cover, and the cam is not sharp on the leading/trailing edge.

major_tom said:

4) Disconnected raw water inlet and outlet hoses from u-cooler. Back flushed u-cooler using 80 psi dock pressure. Water rushed right through cooler. A few tiny pebbles came out. No obstruction apparent.

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You might consider swapping P & S coolers. At cruise, you pump MUCH more water than a garden hose can produce.

major_tom said:

6) Visually inspected raw water flow at idle. Appears about the same on both sides. Good flow. Steam is similar on both sides at cruise, at least from the bridge there are no major differences.

Still have nearly 20 degree temp rise at cruise on the affected engine. (And I cruise in 65 degree sea water).

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As an fyi, I'm cruising in 85 deg water now, no detectable steam from the tower view. My last fix was a new pump cam and cover. That actually eliminated the last of the steam!

major_tom said:

I guess I'll replace both 160F t-stats with 180F t-stats. From there no temp. rise will be apparent. Not much of a fix, though, unless the t-stat on the affected side only opens part way.

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One issue is during warmup. You are circulating very little water thru the exhaust manifolds during warmup from a cold start. And those warm up fast. Faster than the engine. Waiting another 20 degrees of engine temp MIGHT cause some boiling in the manifold, not sure. But, I don't see a good reason for doing the thermostat swap.

Sounds like were in the exact same spot. Frustrating thing is this seems to happen on this motor every other year or so. I typically do all of what you listed and one or some of the things help it to come back down. Guess should do one at a time but much easier to do all at once while cool.

Going to replace the T stat with a 160 today (dont know whats in there), also going to pull end caps and clean heat exchanger.

Will let you know what happens.

Dave interesting thought on the coolers, might try that. Was thinking about switching pumps, but it appears to me they turn in opposite directions so would screw up the impellors correct?

AH ! That steam thing again....Mine have steamed from the day I bought the boat. Usually a 4-5 foot trail. Weather plays a factor in mine and when the trail gets longer, I start to look for developing problems... I see a few steamers out there but only 12-15% of them... A pet peeve of mine that it does this

Thanks Dave.

I don't see a good reason for replacing the 160 F t-stats either. Looking at a previous post I replaced it a little over a year ago.

I thought a saw a post here a year or two back where Crusader now recommends a 180F t-stat instead of the 160F t-stat for fresh water cooled engines? This along with the slight possiblity that my existing 160 F t-stat might not fully open were the reasons for the proposed change.

But a search of the forum did not turn up the post about the 180F t-stat. Maybe I'll just leave it alone. It doesn't go over 180F.

Don't forget that crusader also has changed the style of their exhaust systems.

Also, I can't say I've ever seen an accurate eye for measuring water flow thru anything, especially an oil cooler or a HX. I believe the proven method of bucket and stopwatch, before and after the item in question, is the only reliable way to find a cooling system restriction.

Is it. Possible to retrofit the newer style exhaust on 88 motor?

Yes, bolts right up....did functionally the same thing a long time ago due to cost and availability. Biggest 'surprise' was not realizing the elbows move forward and the exhaust hoses would need to be lengthened.

Interesting thanks, guessing they changed it for a reason, do know in what aspects the design is better?

I can't looked in detail but a first glance, from the external view, they have adopted the center riser style - smaller and lighter so cheaper. May also reduce the quantity of risers needed to stock.

May also not had a choice...many foundries located domestically have shut down.

could also have something to do with their "reduced emissions" strategy (changes coming in the future).

In my case, I had access to mercruiser (and other) parts at wholesale prices. compared to crusader retail, it was a no brainer, even going aftermarket. weight reduction was a big factor. Also got the merc 4" stainless elbows (still in use, today).