1988 OMC 140 hp V4 Thermostats

[Solittle]

I am trying to solve a problem with my two 1988 OMC V4s (Sea Drives) that don't want to idle. They tend to die when put into neutral with the boat in the water. RPMs in the water are 6-700 and 12-1300 RPMs on the trailer with muffs.<br /><br />I believe that part of the problem is that both motors are running cold as the thermostats were either removed or had the "nibs" cut (term a mechanic told me). <br /><br />I want to put in new thermostats. The engines have that large bowl shaped exhauxt cover (for 140 hp I guess) so that access to the thermostats is restricted at best. My mechanic would be glad to do the job but said that the powerheads would have to be removed so that you can have access to the thermostat covers and thermostats. Labor would cost $250.00 to pull the powerheads.<br /><br />I would like to play driveway mechanic and do this myself (preferably without pulling the powerheads) and am looking for tips and "secrets".<br /><br />Both engines run fine otherwise.<br /><br />Thanks,<br /><br />Howard - Miami Fl

 

[Solittle]

Re: 1988 OMC 140 hp V4 Thermostats

^

 

[DJ]

Re: 1988 OMC 140 hp V4 Thermostats

SoLittle,<br /><br />I ASSUME these are crossflows?? Thermostats together at the bottom of the block in a block with three bolts attaching the t-stat block to the bottom of the powerhead??<br /><br />If so, you CAN get to them, albeit a bit tedious, by removing all of the bolts that hold the lower cowl pan. You'll have to remove the covers that attach to the "leg" or exhaust housing to get it to move. These are plastic pieces-so be careful. Once removed, you can pull down on the pan just enough to get the bolts out. Again, a bit tedious.<br /><br />If you do have to pull the powerheads, YOU CAN, do it yourself. If you do have to pull the powerheads, it would be a godd time to replace every hose under the hood. From my experience.

 

[Solittle]

Re: 1988 OMC 140 hp V4 Thermostats

Thanks Djohn19,<br /><br />Yes they are the crossflows and I was hoping to get a reply from someone who has been there done that. I have a 79 manual and the motors look pretty much the same as my 88s. I think I will try your suggestion. If the engines wern't running so well otherwise I would go ahead and pull the powerheads but I don't like to a) do more than is necessary and b) screw around with something that is basically working.<br /><br />Anybody have problems going this route?

 

[FreeBeeTony]

Re: 1988 OMC 140 hp V4 Thermostats

SoLittle,<br /><br />I just replaced the thermoststs on my '89 88hp, I was able to get to the 3 bolts with just a small 3/8" open end wrench. It took some time to remove them but it wasn't too bad...now my overheating problems are gone...and I noticed today that it isn't idling as well. Maybe its running too cold now? Anyway...just have patients and you will be able to do it!<br /><br />Good luck!

 

[Joe Reeves]

Re: 1988 OMC 140 hp V4 Thermostats

SoLittle..... As DJohns has stated, those thermostats can be changed w/o removing the powerhead, and again as he stated in not so many words, it does take a little patience. I've done it many times.<br />--------------<br />FreeBee_Tony... You start out with the statement of replacing the thermostats, but later say that maybe now the engine is running too cold. That engine must run at a certain temperture to compensate for the twisting action in the combustion chamber. Running without thermostats will most certainly result in piston damage. It's more reasonable to install a new complete water pump assy.

 

[FreeBeeTony]

Re: 1988 OMC 140 hp V4 Thermostats

Joe, I replaced both the water pump and thermostats. I also installed a temp gauge that didn't seem to work. I attached a wire to what I believe is the temp sensors (tan wire), the battery and ground on the gauge. The gauge starts at 120 deg F and the needle never reached there.<br />Any tips here?<br />Thanks,........Tony

 

[Joe Reeves]

Re: 1988 OMC 140 hp V4 Thermostats

FreeBee.... That tan wire is strictly to operate the warning horn if you're speaking of the tan wire that is within the engine wiring harness.<br /><br />A temperture gauge requires (and should have come with it) a "L" shaped bracket that attaches to one of the cylinder heads. The "L" shaped bracket has a threaded hole into which a "Sender" is screwed to a point whereas the base of the sender is adjusted so that it is .010 away from the surface of the cyl head. A wire is then run from that sender to the gauge.

 

[FreeBeeTony]

Re: 1988 OMC 140 hp V4 Thermostats

Joe, the tan wire was coming out of the harness ( not connected to anything, had a female connector on it). It appeared to be going to 2 what I thought were sensors in each head. Are these the switches for the horn? The horn goes off intermittently......I really don't think its heat, any tips on troubleshooting the horn? First time I ran this engine (just bought it) I had new gas tanks and forgot to open the vents, I heard the horn and found out later that the horn is also used for the fuel system (vacum) problems. Now when it sounds intermittently I don't quite know what to think!<br /><br />Can I send you pics to show you exactly what I'm talking about?<br /><br />Tony

 

[Joe Reeves]

Re: 1988 OMC 140 hp V4 Thermostats

FreeBee..... The 88hp does not have a warning setup for the fuel system (Fuel Restriction). Also the 88hp does not incorporate a VRO, but rather has a normal fuel pump (you mix the oil with your fuel). The warnings for your engine are:<br /><br />1 - A steady constant beep = Overheating.<br /><br />The engines using a VRO setup have the warnings as follows:<br /><br />1 - Steady constant beep = Overheating.<br />2 - Beep every 20 seconds = Low tank oil level.<br />3 - Beep every other second = VRO failure, no <br />oil, oil restriction, oil/air leak in line.<br /><br />The V/6 engines also have a fuel restriction warning which is the same as overheating, a

 

[Joe Reeves]

Re: 1988 OMC 140 hp V4 Thermostats

FreeBee..... The sensors in the cylinder heads are the overheat warning sensors. Connecting anything to the other end of that system, other than to the warning horn will cause the horn to be erratic.<br /><br />The 88hp does not have a warning setup for the fuel system (Fuel Restriction). Also the 88hp does not incorporate a VRO, but rather has a normal fuel pump (you mix the oil with your fuel). The warnings for your engine are:<br /><br />1 - A steady constant beep = Overheating.<br /><br />The engines using a VRO setup have the warnings as follows:<br /><br />1 - Steady constant beep = Overheating.<br />2 - Beep every 20 seconds = Low tank oil level.<br />3 - Beep every other second = VRO failure, no <br />oil, oil restriction, oil/air leak in line.<br /><br />The V/6 engines also have a fuel restriction warning which is the same as overheating = A steady constant beep.<br /><br />Fee free to send pics if you like.<br /><br />ReevesJ32@aol.com