I/O Cooling System - How does it work?

[Jimmie.jazz]

My buddy and I purchased a 1986 Four Winns 190 with a Merc 230 (Chevy 305) two days ago, and I'm trying to figure out how the cooling system works. It is my first boat, and this is my first post here. <br />I have a Seltec and Clymer manual in transit to me already, yet based on comments I've read here regarding these manuals, I suspect that there will not be a comprehensive theory of operation for the cooling system within either book. What drives my curiosity is the Engine Water Temperature gauge. The needle of the gauge twitches when the key is turned on, but even after 15-20 minutes of running it doesn't register. I suspect that:<br />a) The gauge has failed<br />b) The sending unit has failed<br />c) The thermostat has failed<br />d) An electrical connection has failed<br />e) A combination of above<br />f) It isn't supposed to register (see below)<br /><br />Running it with earmuffs results in plenty of water pumping out of the engine, and a half-hour run on the lake went fine, but I'm leary of running it again until I can verify the gauge is once again working correctly, since hose pressure is different than running in open water, and I didn't think to observe the water output while checking out the boat on the lake prior to taking possession of it. <br />I'm already planning on replacing the lower impeller right away along with all fluids and filters, just to establish a baseline. <br /><br />The demo/checkout driver said that because the water was 60 degrees Farenheit it was normal to not have a temperature reading on the gauge. I asked him what purpose the thermostat served, if it was not to keep the engine at optimum operating temperature. His response was that after 30 minutes the thermostat was designed to stay open all the time, therefore the constant replenishment of cold lake water kept the engine water temperature below the point of registering on the gauge. I asked him to point out the 30-minute timer on the engine, (hehehe) and he replied that the thermostat was held open by internal pressure that accumulated over the 30 minute timespan. Keep in mind he said this with a straight face. I replied that there would be no reason for a thermostat or a gauge at all, if this were true, and that clearly the gauge was not operating properly. He had no further response.<br /><br />So, given the length (sorry) of this post compared to my question, I apologize for the disparity, yet I felt it necessary to fully explain my concern and confusion resulting from the explanation I was given. <br /><br />Where can I find a diagram or explanation of my cooling system, and what troubleshooting procedures would you recommend to restore the functionality of my temperature gauge?

 

[Don S]

Re: I/O Cooling System - How does it work?

<br /> I suspect that:<br /><br />a The gauge has failed<br />b The sending unit has failed<br />c The thermostat has failed<br />d An electrical connection has failed<br />e A combination of above<br />f It isn't supposed to register (see below)

Yes, It's probably going to be one of them.<br />and yes it is supposed to register. It's obvious your demo driver didn't have a clue what he was saying.<br />Best thing to do is forget the Seloc and Clymer manuals and get the OEM Mercruiser manual for your engine serial number and get another one for your drive. It will have all the steps in checking your instruments to find the problem exactly without a lot of unnecessary parts changing.<br /><br />Regarding you cooling system, do you have raw ater cooling, or Fresh water cooling. The Freshwater systems have a round tank with a radiator cap on it where antifreeze goes. Raw water is just hoses everywhere.

 

[Peter J Fraser]

Re: I/O Cooling System - How does it work?

jimmie jazz, <br />Welcome as all would say.<br />a,b, or c are the culprits as you have listed.<br />The first thing to check is c, the thermostat. Remove the housing and have a good look at the thermo. If it looks OK then place it into a pot of water on the stove and bring the water up to temp. If the thermo opens at the right temp (anywhere from 160 - 175 deg) then it should be ok.<br />BUT !<br />Compare it with a new thermostat at the dealers to ensure it is the correct style for the application as there may be some changes in design and if yours is not correct then it may not be working properly when installed.<br />The thermostat is needed to maintain an even temperature in the block, it is not stuck wide open at 60 deg as your salesman suggested. He needs to go to a mechanics school and be reprogrammed.<br />If you have any buddies who are into motor sports they may have an Infrared Temperature Gun that you might be able to borrow. That will give you a very good indicator of what the temps are around your engine.<br />With the correct working thermostat installed you should not be able to hold your hand on that thermo housing.<br />With the thermo working properly you can turn your attention to the gauge if there is still a problem.<br /><br />Regards<br /><br />Peter

 

[Don S]

Re: I/O Cooling System - How does it work?

I'm not sure why eveyone wants to blame the thermostat for anything that happens temperature wise on a marine engine. If that T-stat was taken clear out the gauge would still register. If it was stuck shut the gauge would register.<br />In a marine engine, the thermostat is probably the last thing in the system to go wrong not the first.

 

[Jimmie.jazz]

Re: I/O Cooling System - How does it work?

It's a raw water cooling system, and yes, there are hoses everywhere. It's been raining since I brought it home, so I haven't been able to sit and stare at their routing to determine function and flow. I've seen some nice PDF's for later model years at boatfix.com, but I can't find a main navigation point there that would lead me to a 1986 5.0 litre configuration. <br />Where is the best source for the official Mercruiser manual?<br />Do closed water cooling systems have a lower impellor too? I guess if they do, it is just to cool the internals of the outdrive..?

 

[Don S]

Re: I/O Cooling System - How does it work?

Well Jimmy, to find the exact flow diagram that shows exactly how your thermostat housing and system all works together, you are going to have to get the Mercruiser service manual. You need manual #9, part number 90-14499--1. You can order one from any Mercruiser dealer, or even stop in and they can probably make a photo copy of the flow schematic for you.<br /><br />You can also order a manual online if you have a serial number for your engine.<br /> Order Mercruiser Manuals

 

[Lou C]

Re: I/O Cooling System - How does it work?

The guy who told you that the motor didn't register on the gauge because it was on the water hose was wrong, even with cold water from the hose my OMC will warm up to the rated temp on the thermostat in about 15 min depending on the outside temp. At times the water the boat is in has been as cold as that and it still fully warms up at idle. There must be a problem in the sender, gauge or wiring. If you let run on the hose, you will feel the bottom of the manifolds start to get warm, then the top and the risers will feel slightly warm, and when teh thermostat starts to open, you will feel the top of the stat housing get hotter, and the big hose that goes from there to the engine circulating pump will start to get hot. The manifolds/risers shoud not get so hot that you can't put your hand on them. The thermo housing may though, as it does on my OMC when the stat opens. Get a good Merc OE manual to learn more and trouble shoot it.<br />The Alpha drive has an impeller in the lower unit. This sucks up the water from the lake, and it is pumped to the thermostat housing. Some then goes thru the manifolds, and the rest to the engine. The water is circulated through the engine by the water pump on the front of the engine.

 

[trog100]

Re: I/O Cooling System - How does it work?

seems an awful lot of info required for what is most likely a faulty sender..<br /><br />trog100

 

[Don S]

Re: I/O Cooling System - How does it work?

Sure it's a lot of information trog, but the information was for Jimmie Jazz, not you. And with the information about the manuals he can find out if it's actually a faulty sender or not. What you seem to want him to do is change the sender because YOU say it's the most likely, if that doesn't work, come back and you will give him something else to change and see if that works, if not come back and .........<br />Is that how you want it done SIR ????

 

[Bt Doctur]

Re: I/O Cooling System - How does it work?

Make sure it does indeed have a thermostat in the housing, ground the sending unit lead to the block and check for full scale deflection of the gauge with the key in the "on/run position.<br />"NO"-bad wiring/bad gauge/ no 12volts supplied to the gauge.<br />"YES"- everything fine to the sender plug, replace sender.<br />Even without a therm. you should still see about 100deg. on the motor.

 

[Jimmie.jazz]

Re: I/O Cooling System - How does it work?

This is great support guys, thanks. Hopefully I'll get up to speed on this and can start helping out here, myself. <br /><br />

Make sure it does indeed have a thermostat in the housing, ground the sending unit lead to the block and check for full scale deflection of the gauge with the key in the "on/run position.<br />"NO"-bad wiring/bad gauge/ no 12volts supplied to the gauge.<br />"YES"- everything fine to the sender plug, replace sender.<br />Even without a therm. you should still see about 100deg. on the motor.

Thanks Bt Doctur, I'll give that a shot as soon as it stops raining. <br />

You need manual #9, part number 90-14499--1. You can order one from any Mercruiser dealer, or even stop in and they can probably make a photo copy of the flow schematic for you.<br /><br />You can also order a manual online if you have a serial number for your engine.

Great! Not too expensive, either! Thanks Don S. I have the engine serial number but my outdrive serial numbers are both missing. The upper one is just wiped off, but the lower plate is just gone. I'll look it over in the daylight and maybe I can find another way to I.D. it.<br /><br />Going into maintenance mode...

 

[Don S]

Re: I/O Cooling System - How does it work?

The one for the drive is easy.<br /> Service Manual #6

 

[trog100]

Re: I/O Cooling System - How does it work?

"Is that how you want it done SIR ????"<br /><br />firsly don i work on the principle that questions that get asked on here aint private information.. email is for that..<br /><br />one guy starts a thread.. two hundred guys read it and "hopefully" benefit from whats written in it..<br /><br />my comments are biased towards the bigger lurker type readership i must admit..<br /><br />i dont like simple things over complicated.. i do think that in a general situation folks (readers in genral) might be mislead by this thread hence my comment..<br /><br />i am finding myself having to to reply to your "put downs" on a regular basis don.. there is only one "SIR" on this forum don and i dont think its me..<br /><br />as i said somewhere else do try and tolerate me.. i do u..<br /><br />if my comment sounded a little trite.. it wasnt intended..<br /><br />as for what to do when u have a temp guage that dosnt read.. well yes.. repacing the sender would seem the sensible thing to do.. this last comment is aimed at general readership of course.. not Jimmy in particular<br /><br />as for Jimmies search for Knowledge about how a marine cooling system works.. nothing wrong with that at all.. just as long as folks in general dont think u have to go to all this trouble to fix a temperature gauge that dosnt work..<br /><br />trog100

 

[rodbolt]

Re: I/O Cooling System - How does it work?

what bt doktur says is how I test them quite often. what DonS is trying to do is get a novice used to doing the RTFM method of troubleshooting. what trog is trying to do is toss some parts at it and hope for the best. that sender from merc is close to 50 dollars. if you open the bag its non returnable.<br /> so with the key on engine off momentarily ground the sender terminal. if the gauge gets full deflection its either a bad sender or no t-stat. its not uncommon to see a no register situation with the t-stat removed. so either way a bit of elementary testing may save 50 bucks or so. and that will buy some cool refreshing beverages or a payment on the hair replacements

 

[Jimmie.jazz]

Re: I/O Cooling System - How does it work?

So if grounding the lead to the gauge results in pegging it, then it's likely the sender is bad, or the T-Stat just isn't there at all. I think in this scenario, I'd pull the sender, ground it back to the block from it's threads and drop it in a pan of hot water with it's leads attached. That way, even though I'm planning on replacing (or perhaps really just 'installing') the T-Stat anyway, I'll know for sure. To me, on a car at least, T-Stats are something that get replaced whenever I replace coolant, say every 2 years or so. Sound reasonable?

 

[Don S]

Re: I/O Cooling System - How does it work?

When you ground the sender wire and the gauge pegs, that means the gauge and the wiring are good, and something in the sender is not working.<br />Testing in the water would only help if you do it at several different temperatures and used an OHM meter to check the resistance at different temp settings and compare to book values.

 

[Don S]

Re: I/O Cooling System - How does it work?

Jimmy, I just looked up the OEM Mercruiser parts for your engine.<br />The Thermostat is PN. 59137 and is a 143° stat for raw water cooled engines. $13.60<br />The good news is the Temp sender. It's not the spendy one, it's pn. 97258A1 and only $14.90.

 

[Jimmie.jazz]

Re: I/O Cooling System - How does it work?

Thanks Don,<br />I've verified that the temperature sensor is faulty, so that is good news. I grounded the gauge and it works fine. I boiled some water, and clipped ground & the gauge lead to the sensor and held the sensor in the 180-degree water and there was no reading on the gauge. Then I hooked a regular Chevy 305 sensor to the same setup and the gauge read 'a' temperature, but of course the calibration isn't right. I'm going to go grab a 97258A1 and thermostat /gasket at the local dealer and plug 'er in!<br /><br />Thanks for your help!!

 

[Jimmie.jazz]

Re: I/O Cooling System - How does it work?

Installed the new sensor and all is well. Had to pay 15.50 for it locally, but I wanted it now, instead of waiting. I tested it in a pan of hot water before installing it and it is 'dead on' accurate.<br /><br />Also, I was able to determine the flow and function of the cooling system while I had the cover off of the engine, so now I understand what's going on with it, etc. I'll put together an ASCII description and post it here in this thread in case someone else with the same question does a search.<br /><br />Thanks for your help guys!