stevekouts
New member
Ive got a 1987 4 brl Merc 180
Ive got a 1987 4 brl Merc 180 3.7L thats been giving me some overheating issues. This is a closed loop 50/50 antifreeze cooling system with a 4" heat exchanger. The engine will overheat under load not a real issue at idle. I am not loosing coolant and the compression is very good. I sent the head out for rebuilding and surfacing no cracks. I had the lower drive unit impeller replaced last season the boat stays in the water. There was plenty of pump presure coming out of the lower unit when I checked it and I can see clearly through the heat exchanger with a light. If no load is placed on the engine and you increase the rpms the engine cools down. Its under a load where it seems to have an issue. The timing is fine as well.
At this point the only thing I can figure is the the exhaust manifold and riser may be bad. They are made of cast iron and might be oem. Not sure what the issue is this is not a very complex cooling system but its got me baffled right at this moment.
Any advice or experience with this issue would be appreciated.
Steve
Ive got a 1987 4 brl Merc 180 3.7L thats been giving me some overheating issues. This is a closed loop 50/50 antifreeze cooling system with a 4" heat exchanger. The engine will overheat under load not a real issue at idle. I am not loosing coolant and the compression is very good. I sent the head out for rebuilding and surfacing no cracks. I had the lower drive unit impeller replaced last season the boat stays in the water. There was plenty of pump presure coming out of the lower unit when I checked it and I can see clearly through the heat exchanger with a light. If no load is placed on the engine and you increase the rpms the engine cools down. Its under a load where it seems to have an issue. The timing is fine as well.
At this point the only thing I can figure is the the exhaust manifold and riser may be bad. They are made of cast iron and might be oem. Not sure what the issue is this is not a very complex cooling system but its got me baffled right at this moment.
Any advice or experience with this issue would be appreciated.
Steve