Mercruiser 5.7 liter overheating

[P89Jeeper]

I've got a 1996 Chaparral Sunesta 230 with a Mercruiser 350 5.7 liter. The problem that I;m having is the temp. It's ok in the no wake zone, but as soon as I give it any throttle the temp goes to about 200 or 210, then shoots down to like 160, and then shoots back up to 200. I think my thermostat is sticking, thus the jumping from one temp to another. Also for some reason the guy that usually works on my boat had taken off the water pump to winterize it and I put it back on. Is is just like any other 350 on a car, meaning that the water pump just goes on, or is there something special I need to do. Thanks for the help.

 

[P89Jeeper]

Re: Mercruiser 5.7 liter overheating

btt

 

[retodd]

Re: Mercruiser 5.7 liter overheating

From the way you describe the problem, it sounds like the needle bounces around? If this is the case, then check the connections from the temp sending unit for a loose or corroded connection.

 

[John_S]

Re: Mercruiser 5.7 liter overheating

Don't know why the mech would have removed the water pump from the front of the engine, usually just remove hoses from it. <br /><br />Thermostats don't open and close quickly. If not the electrical issue, as mentioned, maybe air being ciculated. I believe that is one of the issues that can develop with the alpha 1 gen II water pump, in the drive.

 

[bluemist]

Re: Mercruiser 5.7 liter overheating

Hi, <br />Sounds like air. <br />Connect a clear legnth of hose between the transom inlet from the drive to the thermostat housing and run the engine. Look at the hose to see if air bubbles tavel through it. If so; something in the drive is suspect. <br />Exhaust gas fills the dive where the pump sits. If the slinger, or a gromet is bad the pressure will infiltrate the pump and enter the engine.<br />Good luck <br />AL

 

[P89Jeeper]

Re: Mercruiser 5.7 liter overheating

How can I bleed the system if it does have air in it? I looked for the valves that you would see on a car motor to bleed the coolent, but couldn't find anything.

 

[bluemist]

Re: Mercruiser 5.7 liter overheating

It should bleed out by itself. The problem lies in stoping it from getting in.<br />AL

 

[paulie0735]

Re: Mercruiser 5.7 liter overheating

Assuming is not a closed system... I think you will find the thermostat is opening and closing to quickly, I had a similar problem with a 'so called' fail safe thermostat I tried a few years ago. Replace the thermostat with the genuine part OEM part, should solve your problem. Good luck.

 

[P89Jeeper]

Re: Mercruiser 5.7 liter overheating

I took off the thermostat houseing (sorry for the spelling if it's wrong) and the thermostat is stuck up in there. When I have change thermostats on cars, they just come out. I tried pulling it out, prying it out, and nothing. Is there a trick to it?

 

[Fishermark]

Re: Mercruiser 5.7 liter overheating

Does your housing look like this? If so, there is a plastic sleeve that holds the thermostat in. It may be stuck, but it just slides out otherwise.<br /><br />

 

[crazy charlie]

Re: Mercruiser 5.7 liter overheating

My temp did the same thing and it was the stat.You will need a very thin needlenose pliers to insert into the slot between the plastic retainer and the housing.It may be silted up and in that case you will need one of those cheap little razor knives to insert inbetween the plastic retainer and the housing to scrape the crap out so it will eventually come out.

 

[P89Jeeper]

Re: Mercruiser 5.7 liter overheating

That's what it looks like, but I have to wires going to the housing, not one.I pull as hard as I could, but couldn't get it out. I give it another shot, thanks for all the advice yall, I let you know what happens.

 

[crazy charlie]

Re: Mercruiser 5.7 liter overheating

Stop knocking yourself out and break the plastic retainer.It is a $3 item to replace.The retainer may also be brass.If you want to continue to fight it then get one of those small plastic handle knives with a small razor on the end and scrape the crap out .

 

[natwales]

Re: Mercruiser 5.7 liter overheating

I feel your pain. I had a brass retainer. I had to completely destroy mine in order to remove it which was no trouble. I'll warn you though, in my situation there was an equal challenge in inserting the new thermostat and sleeve back into the housing. Although I used all factory mercury parts, I found that the thermostat and the brass retainer ring were of exactly the same diameter and it was impossible to get the thermostat to fit in the ring and into the housing. The only way I was able to get it all back togeather was to very carefully trim back the rim of the thermostat until it would finally fit snuggly into the housing.

 

[bomar76]

Re: Mercruiser 5.7 liter overheating

Easy solution....6th grade physics.....put retainer in freezer, put housing in boiling water.<br /><br />Allow retainer to get good and cold, pull out housing from boiling water with tongs...retainer will drop in.

 

[natwales]

Re: Mercruiser 5.7 liter overheating

well, I didn't have a freezer available or a pot of boiling water available at the time, but I sure did heat up the housing (brass ring inserted) with a propane torch - never did expand enough to allow that thermostat to slip through.