What is normal engine operating temperature

[mr300z87]

After a month long preparation which included upgrading my steering, upgrading to dry joint exhaust, replacing circulation pump, impeller on raw pump (bravo drive external belt driven pump) and a fresh coat of bottom paint my boat is in the water and running great. We have been using it a couple time a week since the holiday weekend. The engine is a 5.7L (see serial# in signature file) I was wondering what is normal operating temperature. I do not believe there is a problem since she has never over heated. My operating temps vary with rpm, at no wake speed 1000 - 1300 the gauge reads about 140 but at cruise speeds 2800-3000 the gauge reads about 165. I do not usually run it much higher than 3000 rpms but when I have for short bursts is gets even closer to the 175 degree hash mark on the gauge. Once back down to idle and or just above the temp drops back down to 140 ish which is just above the half way mark between the 100 degree and 175 degree marks. I have never seen it go above 175 dregees. My engine is raw water cooled, has the cooling hoses to the bottom of the manifold and also to the elbow and I used the pricey merc gasket with the restrictor one side of the gasket (dry joint exhaust). All parts used were mercruiser parts except for the circulation pump. I understand that gauges can be slightly inaccurate and I have not used an infrared gun so I do not know what the true engine temp. However I can say that with the new exhaust manifolds and elbows the temp have been much more consistent. One last thing on the last two outings the air temps have been in the mid 90s with high humidity, and bay water temps are approaching 75 degrees. As always any info is greatly appreciated. Mike

 

[JoLin]

Well, which t-stat are you running- 140 or 160? I run 160's. Port engine (2003) normally reads about 170 and starboard (2014 Quicksilver reman) reads 175-180.

 

[mr300z87]

Per the merc manual I am running a 140 t-stat also a merc part. From what your engines run sounds like mine is good.

 

[stonyloam]

Gauges can be inaccurate, however once warmed (regardless of the thermostat rating) the temperature should hold steady at ALL throttle settings. So it looks like you are not getting enough water flow through your engine. Either you have a pump problem or a restriction in the system that is limiting water flow. You have not overheated yet, but it looks like you are right on the edge. I don't know much about Bravo pumps, but I would recheck the impeller, to make sure it is OK! maybe even consider replacing it with a OEM. Check your thermostat in a pot of water to make sure that it is opening properly, and (don't laugh) make sure that it was installed right side up. Make sure there are no kinks in the hoses, and make sure that water can flow freely into the exhaust.

 

[thumpar]

I run a 160 degree t-stat in mine and it will go a tick over 175 on a really warm day. You should be fine.

 

[hnt]

My 5.7LX EFI Bravo III, raw water cooled, 160deg thermostat runs between 170-175 degrees on the gauge.

 

[mr300z87]

From what all are saying it seems like my engine running between 160 to 175 degrees is normal. BTW I do all maintenance myself so I know it's done correctly. Also I only use genuine merc/quicksilver parts. When time permits I a going to remove the aftermarket water circulation pump an replace it with an oem merc pump with a GM part no that is sitting in my shop. Got burned once trying to save a dollar or 2 by using aftermarket parts. Thanks all for the responses and have a great day. Mike

 

[stonyloam]

I am going to disagree here. The problem as I see it is not that it gets to 175, but that it INCREASES to 175 with "a short burst" of throttle. It should not do that.

 

[boatman37]

a t-stat only controls the minimum temp, not maximum.

 

[mr300z87]

I agree with the statement above regarding thermostats. A few years ago I sucked up some debris and it hung the thermostat open which in turn prevented the engine from reaching operating temp, ran about 100 dregees.

Can any one else verify what stonyloam is saying that it should reach an operating temp and stay steady at that temp no matter what rpm?

Going keep a close eye on it, I have also tested my over heat warning system. This is a 25 + year old raw water cooled engine with just 300 original hours on it used mostly in salt and brackish water but trailered almost all it life.

There is an issue with bravo drives where the hose going through the transom plate gets clogged by corrosion. Do a search for "bravoitis" if not familiar with this, unfortunaly it would be near impossible to check with the boat in the water. Going to do some more research on symptoms of this.

Mike

 

[stonyloam]

a t-stat only controls the minimum temp, not maximum.

I do not believe that is a true statement. The thermostat should allow enough water to circulate to hold the engine temperature stable at any given load. As the engine coolant warms up the thermostat begins to open and allow cooling water to enter the engine. As the load increases more heat is generated and the coolant temperature rises and in response the t-stat opens further to compensate. Once the engine us up to operating temperature the t-stat opens and closes to to regulate engine coolant temperature. Ideally the system should have excess cooling capacity so they the engine will not overheat even under maximum load ( just like your car). In this case with a 140 t-stat if it were stuck partly open it could be stable at cruising speed, and cool off when ideling, but at WOT not enough cooling water is circulating causing the temp rise. If there were insufficient water flow it could be enough to cool at lower RPM and not enough (even with the t- stat fully open) to cool the engine at maximum load. The former is no big deal, but the latter could result in a overheat. Remember this is about a temp spike with a "short burst", we don't know what would happen with sustained WOT operation. If the temperature keeps rising under maximum load, you have a problem that needs to be addressed.

 

[stonyloam]

Guess I should modify my answer a little, the thermostat holds the engine temperature within a specified range, controlling both the minimum, and maximum temperature.

 

[boatman37]

i guess i should say that a properly working t-stat is designed to control the minimum temp, not necessarily the max. a t-stat will only open so far, regardless of the temp setting, as far as i know. so the only control mechanism would be the rate of opening. i would have to research more but i have always been told by race engineers that it won't affect max temps

 

[stonyloam]

Yeah, if the cooling capacity of the system is adequate the thermostat should not have to open fully because the system should have excess cooling capacity. For example in this case with a perfectly functioning system, once up to operating temp, at idle you may use 30% of capacity, 3000 RPM 60% and WOT 85%, and the t-stat opens and closes to maintain a stable temp. If however the system is not up to par at WOT you might need 110% of the available cooling, but the system can not deliver, even with the t-stat fully open, so the temperature will begin to spike. The temp spike with a brief WOT run suggests that at 3000 RPM mr300 is running at near 100% cooling capacity. The test would be a longer WOT run, if the temp stabilizes at about 175, them maybe you will be OK. However if the temp keeps climbing then there is a water flow problem.

 

[mr300z87]

First let me clarify that I can run all day at 3000 rpms and the temp stays steady at 160 - 165 degrees. However if I do a wot run the temperature will slowly climb to 175 on the gauge. I have never seen higher temp than 175. We went out tonight 80 degrees outside 75 degree water temperature and I ran a little higher 3300 rpm with temperature again around 160 ish on the gauge.

When we got to our tie up spot I opened the engine cover the manifolds were hot but I could hold my hand on it, the elbow was warm and overall the engine seem like it should be.

Regardless of the purpose of the thermostat I am going to re ask my original question. What is normal operating temperature for a raw water cooled bravo 1 5.7l carburated engine.

 

[Fun Times]

What is normal operating temperature for a raw water cooled bravo 1 5.7l carburated engine.

Your situation is a little bit different then some of the others because most of the newer engines (with dry joint exhaust) utilize a 160 degree thermostat and a little bit of a different design thermostat housing too.

Your engine utilizes a 140 degree thermostat and a different designed T/housing which by the way they list 2 designs back in 1988 under your serial number 0C386372.

From what I recall with the older designed housings with a 140 T/stat, I'm not used to seeing them run as high as 175 degrees....< But that don't mean it don't, can't or won't run up to 175 as 175 is not to far out of a running range for any of these marine engines regardless of year or housing design. It's just less uncommon is all with your T/housing from what I recall.

If that turns out to be the case then there is a small possibility that the newer designed exhaust system is playing an effect with a higher temp at WOT due to these are warmer exhausts than your old style exhaust were. So like mentioned earlier, the concern would be the spike to 175 at WOT.....While I don't think it's normal for your T/housing design to go that high, 175 wouldn't really be a big concern at this point.....But if you went or go to anything over say a "confirmed" (not necessarily the dash gauge)183 degrees then it would be safe to say you do have a problem someplace and need to find it.

As much as you don't like to go WOT for a long time, at some point you're going to need to run up to top speed to ensure you don't go over the 183* mark as a maximum temp. Most newer engines don't go above 179 max...So I gave you a little wiggle room at 183.

STANDARD COOLING SYSTEM(DESIGN I)
STANDARD COOLING SYSTEM(DESIGN II)
Most (not all) newer engines are using this style housing now,
STANDARD COOLING SYSTEM(DESIGN III - ALPHA)

 

[mr300z87]

Fun Times, as always thanks for the reply, you are the only person that has given an answer to the question I asked. The Thermostat housing I am running is cooling system 2, I did not even consider the different style housing when I purchased and installed the dry joint system. The exhaust system I was running was the standard center mount 4" that would have originally had semi restricted gasket, which when I replaced them the counter guy said this is what you need and gave me full flow type. I do not remember exactly what temps I ran last year but it seems close to what I am running. As I stated in the beginning I am now running the elbow gaskets that are restricted on one side which I believe is the on the side with the bypass hose. See photo


I figured this would be as close to the original design as possible. I suppose I could buy a couple of unrestricted gaskets and try them they are a little pricey though to just try. I can say this the other night I could touch anywhere on the engine with out a problem. Can not say the same for the 383 in my Plymouth.

As far as blockages, I personally work on this engine and have been through it pretty good, so other than bravoitis or an engine block full of crud I am not sure what else to look for. I suppose I could take off the pump output hose and make sure I am flowing as per the specs. This engine is 26 years old and 100 % original with just 300 hours on it, she runs smooth has plenty of power for my little 20fter. As FT stated above even though I never really use full power I want to feel sure that it is running as it should be without the fear of an over heating.

This weekend is supposed to be perfect weather so I am going see if I can get my friend to come a long early Saturday morning to do some WOT testing before the crazies are out. The wife really doesn't like WOT, LOL. I think he even has inferred gun I can use. Where should I aim it at? Thermostat housing, elbow, exhaust manifold, engine, intake manifold, or all of the above. Another question how long do the thermostats last is salt water? I replaced it back in the beginning of boating seasoning 2012, (Merc part) am I do for a new one? I will post my results this weekend. Have a great night

 

[Fun Times]

Fun Times, as always thanks for the reply, you are the only person that has given an answer to the question I asked.

You're welcome but in all fairness to all the other members that have posted above with what their engine is running at temp wise and being open with you to what degree thermostat they know they are running with, their giving you their experience of what they typically see on their gauges like you asked them to do. With the majority of them saying they have a 160 degree thermostat and the highest they usually may see is 175* tells me that they aren't running the same exact setup/design T/housing or same degree thermostat you are running so it makes it a bit harder to get an over all temp that "everyone" is seeing.

In more fairness, The question would be more of what is the older engines (1988 - 1994ish) with the seconded designed T/housing running at to get a better idea for you to go by. With that mentioned, on basic average the most you'd usually see on the gauge is about 15 degrees higher than the temp setting of a normal working thermostat so that's why there is a small concern of your spike to 175* thus far. If it continues to climb than .

My friend has inferred gun I can use. Where should I aim it at? Thermostat housing, elbow, exhaust manifold, engine, intake manifold, or all of the above. Another question how long do the thermostats last is salt water? I replaced it back in the beginning of boating seasoning 2012, (Merc part) am I do for a new one? I will post my results this weekend. Have a great night

Yes!!! Anywhere the cooling system is located, shoot away 'that way you get to know your engine better, Test the temp of the alternator too while your at it.

Well typically you'd know when the thermostat has stopped working as the temp would most likely either be way to cold or too hot depending on where it became stuck.

And as you know running in salt could eventually make the thermostat react slower sooner vs. running in fresh which makes it difficult to put a time frame to it's expected life span.

Without recalling the exact temps you ran last year with the old exhaust makes your question a bit more difficult to say if you have a problem or not because technically while you've reached the higher end of the spectrum for you engine model/designed T/housing, etc., you haven't actually overheated.....'Yet and you may not. If you do, then personally I might start with a new thermostat before going into full test mode all the while bearing in the back of my mind that there's one potential weak spot on your stern drive model which is the water pocket cover & seal that could start to suck in hot exhaust at higher RPM. Item numbers 2 - 6, http://www.mercruiserparts.com/Show_...AND+DRIVESHAFT

^ Of course you've been here on iboats long enough to know by now that your impeller better be in tip top shape.:black_eyed:

 

[mr300z87]

I meant NO offense to any one here on Iboats as all have been great over there years. I have a Bravo 1 drive, external belt driven water pump so no water pocket issue there. More concerned about this (Bravoitis), but my drive is super clean for being 25 years old as this was a trailered boat.


The impeller was replaced with a Merc part back in June as part of my preseason prep. I will post more this weekend after some testing.

 

[thumpar]

I would use the heat gun before worrying about it much more. The gauges can be off by a bit.