New engine in, now both temp guages just read off the dial

[rcon]

First, the story and my apologies, it is a little long.

Just had new engine dropped in.

During sea trail with the mechanic, noticed new engine (port)was now reading significantly high (200F). We hand checked riser and t-stat housing, both appox 75C/165F (I make a lot of milk for coffee and know my 65C well :grin. At this point we suspect the new engine just reads "different" and this is to be the "new normal"

Ran her home for 3 hours, 20 min on the plan @3800RPM, then 10 min 2500-3000rpm as per recommendation from mechanic. Starboard ran at it's normal 160F-ish, starboard at 200ish (as per sea trail)

Fired up yesterday, and both gauges read off the chart, hard to the right.

Port (new engine), was quickly up to temp on both its riser and t-stat housing and all was well
Starboard, both risers and t-stat remained cool, then one riser started to get warm (but well less than 75c/165F), t-stat a little warm but nothing like the riser

Based on this we start 30 min out puttering around outside the marina in the 1000-2000rpm range so my old man could play.

Now, berthing was a little challenging as wind picked up, so I didn't get a chance to test this immediately, but approx 3-5 min after engine shutdown, the riser on starboard was, I would guess, at around 50C/120F, leading me to think it had started working as per normal.

One more thing (making me this I've got a short of some sort), 4-5 times during the trip, the new engine's oil pressure gauge would sharply drop to 0 and spring right back up to normal.

Now the story out of the way, some questions,
1. Is this hand testing of t-stat and risers a valid way to check operation of cooling system? (I'll be buying an IR temp gun today)
2. Is there likely to be any common link between temp senders, a short possibly?
3. With one riser much cooler than the other, I assume intake is one side, exhaust the other - correct?

As per above, let me see if I've got this right, water gets picked up thru my alpha one drive, pumped into intake riser, t-stat measures the temp of engine somehow (exhaust gasses? block?) then opens up and allows raw water to flow around the block, gets mixed with exhaust gasses and is expelled via the other riser thru the drive at the center of the prop. Temp sender unit runs from the block, not the t-stat housing. Have I got all that right?

 

[Lazy Daze]

Seawater comes directly into the t-stat housing. Although, it will pass through your power steering cooler and fuel cooler (if you have EFI) on it's way.

The t-stat opens/closes based on the temp of the water in the block. It is normally closed. As it heats up (from block water), it starts to open. When it's closed (cold block), the water then goes directly to the exhaust. As the block heats up, the t-stat starts to open and allows the seawater to mix with the water already in the block.

Both exhaust manifolds are just that - exhaust. The manifold will be just exhaust (gas) -- water and exhaust (air) will mix higher up (basically where the hoses from the t-stat housing connect to the risers).

Yes, using your hand on top of the elbow is a very good way to judge temperatures. You should not have to remove your hand. It is also normal for one elbow to be hotter than the other - this is just due to the way water flows through the t-stat. I've IR'd elbows, but don't remember the exact differences. It will also change slightly from engine to engine. Just giving a round-a-bout guess, I would say that the difference is probably never more than about 20* from one elbow to the other. One side typically feels "warm" to "quite warm" while the other feels "cool" to "warm".

 

[tdschafer]

I'm not sure I follow you 100% but let me see if this makes sense. You think the water enters one riser and exits the other? Also as you stated this is a raw water cooled motor or motors.
As I understand it that is not the case. Your alpha-1 does pump the water up to the motor. This water is received at the circulating pump on the front of the engine. It is then pumped up to the t-stat housing where it gets distributed. If the engine is cold then the t stat stays closed and the water circulates around the exhaust manifolds and thru the risers where it meets the exhaust gases. They then pass out together thru the out drive. Once the motor reaches temp, some of the cool raw water circulates thru the block to maintain temperature then mixes with the manifolds, risers and out the out drive. That is the main just of it as I understand it. If it was fresh water cooled then a heat exchanger comes into play but I don't think that is the case based on your post.
Also, if you are looking for a very general difference in temps I guess the hand touch method is ok but, since it is not calibrated I wouldn't be placing a temp value on it! The IR gun is the way to go and they are relatively cheap from Harbor Freight.
I hope this helps! Goid luck!


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[tdschafer]

Damn Dennis!! You typed faster than me!! LOL And you had better information too!!


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[Lazy Daze]

Sent from my iPhone using Tapatalk

That's only because I'm on a computer - and even at that, you were awfully close!

 

[rcon]

Thanks guys, very informative. This community is fantastic. As for putting a temp on it, I measure my milk temp when frothing it (65c), and I'm a very good judge ;-)


Any ideas on what both gauges might have spat it at once? I'll give my yard a call in a bit, hopefully they're open this time of year!, but its always good to have an understanding of what I'm asking about before I call.

 

[rcon]

Follow up. by implication, if the t-stat housing is at 160f/75c I can assume the cooling system is working regardless of the temp gauges? This is obviously only a stop gap measure until a fix can be found.

 

[Lazy Daze]

Follow up. by implication, if the t-stat housing is at 160f/75c I can assume the cooling system is working regardless of the temp gauges? This is obviously only a stop gap measure until a fix can be found.

I think I would rely more on the risers as a good indicator. Since they are the "final answer", so to say.

I'm a little confused on your initial post, too. Would you mind reading back through it and see if it all makes sense? For one, it seems like you're referring to the stbd engine when you should be referring to the port - or vice versa.

One thing that can make a gauge read funny, though, is not putting the t-stat/gasket/spacer in correctly.

The oil pressure gauge reading funny... I take it the alarm never went off? Since it didn't, I highly doubt anything is seriously wrong. It could be a piece of dirt on the sender, but I would lean towards the sender being on the fritz (bad). Change the sender or swap with the other engine if you want to verify.

 

[Lazy Daze]

Oh, here's something easy you can do to get a better idea of how your cooling system works. It's one thing to have it explained in writing, but you'll probably make much more sense of it if you touch/feel it yourself...

Start at your t-stat housing and simply follow your hoses. Start with the intake hose - it's the one on the port side of the housing, front. It should not have another one the same size as itself and it will be the smaller of the two "oddball" sized hoses. The other oddball one is the big one that goes from the housing to the circ pump.

Back to the intake hose - you'll see it eventually goes towards the back of the engine and hooks into the inner transom plate (the big black thing attached to the transom wall), but it will hit the power steering cooler and possibly fuel cooler along the way. When you get to these coolers (round tubes, basically), you'll see two small diameter hoses attached. Follow these hoses and you'll end up back at the power steering pump and, respectively, the fuel/water separator. You get the idea - just start following hoses/lines and you'll get a better understanding of things.

Plus, it forces you to take a good long look at the various components (good for general maintenance, checking for leaks, etc).

 

[Jimmy Buoy]

I stepped away for about an hour... I'm obviously a bit late...

What a great site to be so responsive!! Well done guys!!

 

[rcon]

I think I would rely more on the risers as a good indicator. Since they are the "final answer", so to say.

I'm a little confused on your initial post, too. Would you mind reading back through it and see if it all makes sense? For one, it seems like you're referring to the stbd engine when you should be referring to the port - or vice versa.

Thanks LD. No, its all correct, but I was confused when writing it, so my post reads equally confused.

Basically one engine, the shiny new (not recon'd!) port engine behaved exactly as it should and I could touch everything for a 3-4 seconds before having to remove my hand from one of the risers/t-stat housing. Temp gauge was jammed over well above 200F, and appeared to be touching the side of the gauge.

Other engine, not-so-new (rebuilt head 18months ago) starboard engine performed well, but *both* rises and t-stat housing remained cool for a long time, then finally the t-stat housing and one riser finally got "warm", but not nearly as warm at the other engine. t-stat housing did seem appropriately warm a few minutes after we berthed. Temp gauge was *also jammed right over well above 200f*, this gauge until yesterday would sit right at 165/170f. Neither showed signs of dropping by the time we departed 30min later.

So the post boils down to .... "can I assume my cooling system is working if the t-stat housing/hotter elbow remain at appox 165f?"

lol'ing at myself for thinking one was intake, one exhaust.

Many thanks all for contributions so far and I'll be tracing my water lines shortly!

 

[Bob & Sue]

First, the story and my apologies, it is a little long.


One more thing (making me this I've got a short of some sort), 4-5 times during the trip, the new engine's oil pressure gauge would sharply drop to 0 and spring right back up to normal.

Everyone else has covered your cooling issue +1 on getting an IR gun I use a Raytek Raynger ST60 very accurate. I had my engine out July 2011 to replace the coupler by the Sea Ray dealer after getting it back my water temp gauge would sometimes work fine or not read at all then start working a couple days later the oil pressure gauge starting bouncing from 0 to normal. Sea Ray sent out a 20 year plus experienced Mercruiser mechanic checked both gages by shorting out the pins both worked, he then pulled the wiring harness connector apart on the engine and found corrosion on several pins. After scraping off the corrosion and putting some die electric on the connector housing mating surfaces (not the pins it will not conduct electricity) all gauges worked like they should.

I'd be concerned about a mechanic that would just let you run at 200 degrees saying it was ok with a new engine.

 

[Lazy Daze]

So the post boils down to .... "can I assume my cooling system is working if the t-stat housing/hotter elbow remain at appox 165f?"

It sounds like you have a simple electrical issue. Now, when I say simple, take that with a grain of salt since we all know that electrical gremlins aren't always "simple". But if you can comfortable keep your hand on top of the elbows, then you are OK. You also have a high water temp alarm that will go off. Since the engine didn't physically feel hot, chances are the alarm is functional and you just have something funky going on with the gauge or sender.

As far as the port engine being cool, that could be explained by something being stuck in the t-stat. Like I mentioned above, it's normal for one elbow to be warmer than the other. Using your hand is also a good method for testing. But where the hand method fails is that it's hard to convey that "feeling" via a forum. And again, that 20* difference I mentioned is just a general guess.

What would I do?

Start by checking all connections, like Bob mentioned. The fittings that have only a single wire going to them will ground through where they screw in. You might want to remove, clean and reinstall.

I would also pull the t-stat housings off (and t-stat out) and check for obstructions in both the t-stat and the housing (look inside). When you put it back together, make sure the little copper contacts in the housing gasket will make a good contact with both the housing and the block. It's best not to use any grease here. If either of the t-stats are more than a few years old, just replace them.

Are both t-stat's the same? Meaning, do they both have the same temp rating stamped on them?

Are the impellers good? You can test them by running the intake hose into a bucket and time it for 30 seconds. Then compare to the other side. I can't remember exact numbers, but I seem to recall that in 30 seconds, you should pretty much fill a 5-gallon bucket (if the boat is in the water).

And, for what it's worth, I do like using an IR gun. Just don't get too caught up in small differences from one engine to another or even when comparing one spot on a particular engine at different times.

 

[rcon]

Update.

No IR gun yet (so much choice!), but engines and gauges all ran fine yesterday, with "hand test" also suggesting everything was in order. Everything seems to be pointing toward a contact/corrosion/short issue

Did speak with the guy who did the work before we went out and we'll go over the gauges/connections when we slip later this year.

I'd be concerned about a mechanic that would just let you run at 200 degrees saying it was ok with a new engine.

Whilst the gauge read 190-200, t-stat housing was similar temp to other engine and I was able to hand on there comfortably for 3-4seconds.

Again, thanks for all your advice/input. It is fantastic to have some idea what I'm talking about when I call the yard so I can at least preempt some information gathering/not be taken for a fool

(I have good relationship with my yard, that was tongue in cheek)