Overheating at idle

[Rob_bie]

Hey there, looking for some help.
Engines Over heating on my 1990 5l merc at an idle. The engine itself is a new rebuilt long block. So far I have changed impeller system, circulation pump. Removed exhaust manifolds and elbows and then gave them the acid treatment. Flow is good. No kinks or blockages in any hoses. I have the t ball system thermostat housing with new 140 thermostat. I have on order the Sierra 18-1989 to see if that makes a difference. I am open to suggestions if anyone has any.

 

[kenny nunez]

Look inside the thermostat housing, there is a metered orifice which is the “by pass” when the thermostat is closed. If it is corroded shut the engine will overheat.

 

[Rob_bie]

Thanks for some input, I’ve had the housing out cleaned and inspected. It looks good, everything is free. Numerous mechanics are also baffled on it, I should add it’s an alpha one gen 1.

 

[Kola16]

What is telling you that it is overheating? A gauge? An alarm? Have you confirmed the temperature with an IR thermometer?

 

[Rob_bie]

Dash gauge and I’ve used a temp gun aswell.

 

[Scott06]

Hey there, looking for some help.
Engines Over heating on my 1990 5l merc at an idle. The engine itself is a new rebuilt long block. So far I have changed impeller system, circulation pump. Removed exhaust manifolds and elbows and then gave them the acid treatment. Flow is good. No kinks or blockages in any hoses. I have the t ball system thermostat housing with new 140 thermostat. I have on order the Sierra 18-1989 to see if that makes a difference. I am open to suggestions if anyone has any.

the balls in thermostat housing are supposed to restrict flow of raw water to elbows, if they have debris could be passing too much water into exhaust starving the engine of cold water.

Are you sucking air in at impeller if lower housing is corroded or water dam in there is damaged this can happen - did you use a cheap impeller or OEM? Replace housing too ? This is a gen one ?

You can put a clear hose in feed up from drive to see if any air bubbles

 

[zellerj]

My alpha 1 overheated after an impeller change because the copper tube caught and turned the rubber insert sideways in the water tube housing.

Another thing to check is that the water intake hose is not kinked. If it is kinked, it cools when turning in one direction, and warms up turning in the other direction. Or sometimes if the hose is kinked trimming your outdrive up a bit also allows it to cool.

I agree that if the part is rubber, buy OEM. This includes impellers and bellows.

 

[Bt Doctur]

can aslo remove the drive and put a hose into the inlet hole