1994 7.4L Bravo Gen V temperature

[JGabeH]

I have a 1994 24' SeaRay with a 7.4L Bravo engine in it. I'll have to head to the marina tomorrow to get the serial number. I've owned the boat for about 5 years but have recently started doing the maintenance on my own. The temperature in my boat (per the gauge) has always run around 160-165 degrees F. The other day I was making a WOT run and felt like there was a loss of power for a second but I'm not sure. My eyes jumped to the temp gauge but it only read 170F. After reading online, I found out that my engine has a 140F thermostat in it. Is my temperature way too hot?

Since this episode, I changed the raw water pump impeller and housing, thermostat, water separating fuel filter, and temperature sending unit. I took the boat out today and it still ran around 165 degrees F and crept up to 170F as I backed off the throttle after a 3/4 throttle run. It doesn't seem to go above 170F. It seems to cool down to around 160F when getting up onto a plane at WOT then slowly works its way back up.

At this point I am wondering what direction to go or if anything is really wrong. My next thoughts would be to back flush the cooling system and check the exhaust risers/elbows as I have no idea if they are original or not. Any suggestions are appreciated.

Thanks,

Gabe

 

[Scott Danforth]

welcome aboard.

first, the gauge on the dash is merely an aproximation. an infared thermometer is a handy tool to tell you the actual temp the motor is at, and in various places

you have owned the boat for 5 years, is this a salt water boat? if so, pull your manifolds and risers and inspect them. they could be clogged with rust and near needing replacement.

also, early Bravo drives have a water supply tube corrosion issue where the tube goes thru the transom plate. there is a kit to correct it.

generally if your boat ran a bit cooler than now, you are experiencing a water flow issue. either water comming into the motor is restricted, or water exiting the motor.

 

[alldodge]

I'm thinking two things, either you have a 160 degree thermostat in it (thinking you have a 140), or your running in pretty warm water.

Might be wrong, has happened many times before

 

[JGabeH]

Thank you for the quick replies guys. First off, the boat has been a freshwater boat all of its life (almost). I lived in Florida for 10 months and used it about 5 times in salt water. It was flushed very well each time. I can tell you currently that it is a 140F thermostat, not a 160. It had 140 engraved right on the rim of it (also I know I ordered a 140). As far as water temp, I'm in northern Georgia in a spring fed mountain lake. The water temp currently is probably in the upper 60s or 70... or less.

As far as the water supply tube corrosion, is this something I can check without pulling the drive? That is one maintenance item I have not yet attempted. Could I check the waterflow at one of the hoses to see how the pump is pumping? I will probably order a gasket kit for the manifolds and risers so I can pull them and check them out. I can hold my hand on the riser elbows for as long as I want... they do not get very hot. The process removing them seems straightforward enough. Finally, I'll buy a temp gun. What places on the engine should I shoot to get the most accurate running temperature?

Thanks again for the quick replies. Any other input is greatly appreciated.

Thanks,

Gabe

 

[alldodge]

The water hose connection is on the transom assembly where the hose connects to it. They can clog and get pretty messed up, but it doesn't happen so much in fresh water. It is tight back there but here is one which was pretty messed up.

Wonder if it could be circulating pump, don't know

 

[HT32BSX115]

Howdy,

Welcome aboard!

If I am not mistaken, you should have an oil cooler in the raw water circuit after the raw water pump, but prior to the T-stat housing raw water input.

If you (or a prior owner) had a full/partial raw water pump failure, pieces of that pump could have ended up in the oil cooler. It would still pass water but it wouldn't be unrestricted.

Mine was almost completely plugged but the engine didn't overheat. I had to use needle-nose pliers to get the debris out of the oil cooler. simply "back-flushing" wouldn't move the pieces at all!


Regards,


Rick

 

[JGabeH]

I do have an oil cooler between the raw water pump and that T stat housing. When I changed the impeller this year I tried to remove the hoses to the oil cooler but they are quite low in my bilge with very little arm room. I will have to figure a way to get them off and get an inspection camera into that oil cooler. If there are pieces, I'd have to remove the cooler to be able to get needle nose pliers in. Do I need to drain the engine oil completely before removing the oil cooler or can I just under the lines without a bunch of oil running everywhere?

I purchased an infrared non contact thermometer. Where should I check on the engine to get the most accurate running temp?

 

[alldodge]

Very good point HT good catch. Jgabeh, the oil cooler is for the power steering pump.

 

[HT32BSX115]

I do have an oil cooler between the raw water pump and that T stat housing. When I changed the impeller this year I tried to remove the hoses to the oil cooler but they are quite low in my bilge with very little arm room. I will have to figure a way to get them off and get an inspection camera into that oil cooler. If there are pieces, I'd have to remove the cooler to be able to get needle nose pliers in. Do I need to drain the engine oil completely before removing the oil cooler or can I just under the lines without a bunch of oil running everywhere?

I purchased an infrared non contact thermometer. Where should I check on the engine to get the most accurate running temp?

You may have both an oil cooler and a power steering cooler or a combined cooler for both.

Mine is a 97 model (GEN VI) 454. It has separate oil and PS coolers. My oil cooler is actually on the front of the engine, on the Port side, mounted vertically. The PS cooler is horizontally mounted on the Port side below the exhaust manifold.

The raw water hose goes from the raw water pump discharge, under the engine and to the back of the PS cooler on the side.

Then there's a hose from front of the the PS cooler to the bottom of the oil cooler mounted vertically on the front Port side of the engine. The (raw water) output of the oil cooler then goes to my aftermarket San Juan Engr heat exchanger.

I have not experienced a raw water impeller failure since installing the closed cooling system. I have had a plastic housing crack though,

I had to remove the oil cooler to see inside. (the previous owner of my engine told me that he'd replaced the impeller and it was still intact......... (....those pieces had been in the oil cooler for quite some time!!!)

Point your IR thermometer right at the T-stat housing (intake manifold side) which is usually where the temp sender is.

//

 

[JGabeH]

My 454 is a Gen V and only has one cooler. The raw water pump outlet has a hose that goes into the rear of the oil cooler that is mounted on the bottom port side of my engine (WAY down in my tight bilge). The outlet of the oil cooler has a hose than bends around the front of my engine to the top and into the TStat housing. If I remove the fittings in the oil cooler, will all the power steering fluid and/or oil leak out all over my bilge? I have very tight access to reach that oil cooler. I think my first action will be to remove the water lines from the oil cooler and look inside with an inspection camera. If I identify impeller parts... I'll have no choice but to pull it some how.

This weekend I will let it warm up to 165F on the temp gauge then start shooting with my infrared thermometer. Maybe it's not even running hot. To be clear though, with a 140F thermostat, the temp at temperature sending unit should be 140F, right?

 

[Bondo]

I think my first action will be to remove the water lines from the oil cooler and look inside with an inspection camera. If I identify impeller parts... I'll have no choice but to pull it some how.

Ayuh,.... You should be able to just back-flush the cooler with a garden hose,.....

Water in, in the hose at the t-stat housin', 'n water out at the 1st connection beyond the cooler,....

 

[HT32BSX115]

I think my first action will be to remove the water lines from the oil cooler and look inside with an inspection camera. If I identify impeller parts... I'll have no choice but to pull it some how.

If you can see inside, I wouldn't hesitate to try to flush it backwards using a garden hose...........it didn't work for me, but it may work for you. And since you can see well using the small camera, you'll be able to tell right away if it doesn't work.........

This weekend I will let it warm up to 165F on the temp gauge then start shooting with my infrared thermometer. Maybe it's not even running hot. To be clear though, with a 140F thermostat, the temp at temperature sending unit should be 140F, right?

If you haven't verified your temp gage, you should!

Your temp at 165 is not all that hot. Mine has a 160 deg stat. It runs closer to 180. It's quite normal.

Now, having said that, Since you have an easy way to see with the camera, you should STILL look into the inlet of the oil cooler to see if there's any debris in there.

 

[JGabeH]

Sorry about my absence the past couple of weeks. I finally got a chance to go down to the boat with my temp gun and verify some temperatures. I did most of it at idle. My temp gauge on the dashboard reads 165-170F once up to operating temperature. The following are temperatures from my temp gun:

1) Thermostat housing (warmest point on it) near the hose exiting to the starboard exhaust manifold - 143.9F
2) Thermostat housing where the temp sending unit is fitted - 137.0F
3) Port Exhaust Manifold (hottest point I could find on it) - 169.5F
4) Starboard Exhaust Manifold (also hottest point) - 172.2F

Temperatures on both risers were between 95-105F at any given time.

Should any of those temps give me any concern or at this point can I assume my temperature gauge on my dash reads 20-30 degrees high?
Anyone recommend a specific brand/model of temperature gauge? Or should I just subtract 20F from the reading and keep the current gauge?

Any thoughts are greatly appreciated.

 

[alldodge]

Remove the wire off the sender and with an ohm meter measure the resistance.


If the resistance is off from what is shown, remove sender and put in a pan of water and retest.

 

[mr300z87]

Here is one more thing to check the reading on your gauge, last year I notice when I put a load on my power supply to the dash (running light) I would notice my temp gauge (other gauges as well) to show higher temp then normal. So check the 12 V supply to the gauges. This year I added a new circuit up to the dash to take the load off the supply to the instruments. BTW those temp numbers I got last year doing the same tests for the same reasons. With minimal load on dash circuit the gauge was really close the housing temp with the IR gun.

 

[JGabeH]

Thanks for the advice. I'll check the sending unit resistance, but I replaced it this year thinking it may have been the problem. It reads the same as the old one.

What would I have to do to run a new circuit for the gauges? Just run a wire from the battery switch to the gauges? My voltage gauge always reads lower than the actual battery voltage too.

 

[JGabeH]

Well, I'm back to having overheating issues after storing the boat for winter. I don't have any water in the oil and don't see any leaks so I don't believe anything froze. Other than fogging, oil change, etc, I winterized the boat by draining the water and refilling with RV Antifreeze using my Superflush system (which supposedly you can just run antifreeze through it to winterize without draining). The temp at the exhaust risers rose to near 200 and at the temp sending unit on the thermostat housing to near 180 before I shut it down. I changed the water pump impeller last year and all the hoses seemed to heat up so I believe at this point that water is at least flowing. The thermostat and temp sending unit was also new last year. Any thoughts? The only thing I wonder after some research, and I hope its not the case, is that because the boat has been run in salt water a few times, the antifreeze turned to gel? Does RV Antifreeze do this or just normal cooling system antifreeze. Any advice or thoughts would be greatly appreciated. I'm feeling a little lost now.

 

[alldodge]

I winterized the boat by draining the water and refilling with RV Antifreeze using my Superflush system

I'm thinking you burned up your impeller. The problem with these flush systems is they are restrictive. My guess is the motor was running and trying to suck the antifreeze in, and was not able to do it very well and burned the impeller.

 

[JGabeH]

Sorry. I should have specified that with the Superflush System the boat was not running while running antifreeze through the engine. If it had been, I would have considered burning up the impeller a prominent option. The Superflush System just replaces the plugs in the bottom of the block with ports and it adds T's into the water lines before the exhaust risers. This allows water (or antifreeze) to flush through the engine on both sides of the thermostat without running it up to temperature and using a flushing device. The Superflush manifold pulsates the water through these areas when pumped through. I do agree though, the T's that are in the lines do slightly restrict flow but have not caused hot temps like this. Any other thoughts would be great. Can thermostats go bad sitting over the winter even if they were new?

 

[alldodge]

It would be rare for a thermostat to go bad but can happen. Most over heating issues come from the impeller. Pull the hose coming from the pump to the thermostat, get water running or better have the boat in the water. Have a 5 gallon bucket and see if the water comes out with force. If its in the water the bucket should be filled in 20 seconds.

The issue with your exhaust being hot makes me think its not pumping water. If the thermostat was stuck closed then the exhaust would be warm but not hot. The water bypasses the motor when the thermostat is closed, so water continues to flow out the exhaust.