Are these temps normal??

[Lucrative]

I have a 2000 Chaparral 270 with a 7.4 MPI with raw water cooling (run in salt water). Toward the end of the season last year, my temp gauge quit. I would typically run a right at 160 or a tick below once it got up to temp. This year, I just replaced the water temp sender and the gauge. I put it on the muffs to see check out the gauge, and it steadily increased up to about 200 on the gauge. Seemed wierd, so I got the infrared temp gun and I got these temps.

(All at idle on the muffs after idle for 20 mins)
On the t-stat housing by sender -125 gets to be about 135 toward the front of the housing, down under 110 at the closest point of the engine
Below the t-stat housing where the water flows in/out of the block- 155/160
Shooting the point where the exhaust manifold touches the block and the very bottom of the manifold got me some really high numbers (up to 240 or 250, but sometimes was like 190s)
Top of the starboard riser ran around 120 or so with variations a bit lower and higher

I tend to think that I got a faulty temp gauge, but when I was messing around looking at the temps around the exhaust manifold and block, I was kinda concerned because they seemed so high. Also, I thought the risers were supposed to be running a lot hotter than that at the top. Is this normal or not?

Also, I put the boat in the water before I got ahold of the infrared gun, and it did the same thing, climbed up to 200 and just sat there. I ran about 2 miles at 30 mph and then turned around and ran 2 miles back. All seemed to be well except for the temp reading.

 

[Scott Danforth]

I would be looking for a blockage somewhere. should not get over 180 anywhere, however possibly the very flange meeting the block (no cooling passages there)

 

[wrench 3]

Don't worry about the temps on the exhaust manifolds near the cylinder heads. As Scott said there is no cooling for the 3/4" or so between the head and the actual manifold. Since the combustion temperatures are around 1,200*f it can get rather hot there.
Do you have the correct temp sender for your number of gauges (single or dual station)?

 

[Lucrative]

Temp sender was Sierrra part #18-5897, which I crossed from Mercruiser part #97257A 1
Gauge was Sierra part #63480P

I believe those are both right, but I could be wrong. I have tried and tried again to find a blockage somewhere in my system, backflushed the cooling system, took all the hoses apart, checked the strainer on my oil cooler (my power steering cooler doesn't have a strainer), checked flow from the impeller, etc. I just don't see a water flow problem at this point. The only thing I can think is that maybe I have accumulated sand/sediment in the block somehow...but when I put the temp gun on the fixture right by the short water hose coming from the main water pump, it was reading 160, so that makes me think I'm not blocked off in there. I dunno, kinda lost at this point unless the gauge is just faulty.

 

[wrench 3]

The Sierra 18-5897 is for dual stations ( for example - One set of controls and gauges in the main cabin and another on the fly bridge). Is this the setup that you have?

 

[Lucrative]

I don't have a flybridge. I only have controls and gauges in the cockpit. Isn't the part number for the dual station was Merc #49734? I looked online at a few reviews of the Sierra 18-5897 on Amazon and people say it reads up to 190 for them as well, so I feel ok that I'm not overheating at least. I guess there's some resistor that can be added to the sender so it reads right according to one of the amazon reviews.....how annoying.

Just looked it up....Sierra dual station is 18-5898, the one I got was supposed to have been 18-5897, but I didn't look at the bag when it came, I just put it in. I think I got sent the wrong one.

 

[wrench 3]

The 18-5898 and the 18-5897 are both for dual station. The 18-5898 just has a larger thread were it goes into the engine.
The one you need is the Sierra TS26621 which, by the way, Sierra says is there replacement for the 97257A 1.

 

[Lucrative]

Closing up the topic here. I was getting the wrong temp sender. I have the right one in now (per wrench 3) and I'm running at normal temps. THANKS!!

 

[wrench 3]

I'm glad that you got it all sorted out. And an easy fix at that.
Happy boating.