Hello all. New to this site and have a few questions. I just purchased a 1978 Searay 18.6 with a 305 V8 MerCruiser. It runs hot when plained out, temp comes back down when idle. The previous owner told me he had lower unit impeller replaced because it was bad, and it still ran hot. He also replace water pump on engine. He thinks some of the impeller debris, or other fourign material causing a restriction somewhere?! Is this possible? If so where should I be looking? Anything I may be overlooking? If the outdrive need to be serviced, is it a big job? Thank you in advance.
Runs hot when plained
- Thread starter churchill
- Start date
tdappleman
Active Member
- Dec 17, 2007
- 1,608
- Boat Info
- 1996 270 Sundancer
- Engines
- New twin 4.3's - 235hp each with Alpha 1 Gen 2 Drives
I'd start with the exhaust system - how hot do the risers get when running? You should typically be able to hold your hand on them - so warm but not too hot. Next would be the thermostat since at plane you will be running a higher RPM - may be stuck or partially blocked.
blorincz
New Member
- Sep 24, 2007
- 40
- Boat Info
- 2002 310 Sundancer
- Engines
- 350 MAG's w/ V-Drives
Have you had the actual engine temperature checked to see if it's indeed running hot? I had the same symptom and it ended up being the temp gauge sending unit.
BillyT0020
New Member
If its running hot at higher RPM's its usually the exhaust manifolds or risers are corroded internally. If its running hot at idle, like mine is currently :smt013 , then its the impeller or water supply side. I would replace the exhaust manifolds and risers, they are probably long over due anyway.
Good Luck!
Good Luck!
tdappleman
Active Member
- Dec 17, 2007
- 1,608
- Boat Info
- 1996 270 Sundancer
- Engines
- New twin 4.3's - 235hp each with Alpha 1 Gen 2 Drives
For the exhaust check - put your hand on the risers themselves and check the temp. I'm not sure what they would look like on your year motor - maybe something like this:
The risers are the portions of the exhaust which rise up and turn towards the rear on each side of the motor. If water is circulating correctly in each they should be warm to the touch but not so hot you cannot touch them. If they need to be replaced the cost depends on if you go with Mercruiser parts which from others feedback appear to be of higher quality and will last longer. There are aftermarket brands like Osco which are cheaper but may not last as long. The labor can be extensive depending on how difficult it is to get to each side and how rusted the bolts are. Make sure you use new gaskets when you do the work. Here's a link to help you get started: http://www.ebasicpower.com/exhaust/ .
The risers are the portions of the exhaust which rise up and turn towards the rear on each side of the motor. If water is circulating correctly in each they should be warm to the touch but not so hot you cannot touch them. If they need to be replaced the cost depends on if you go with Mercruiser parts which from others feedback appear to be of higher quality and will last longer. There are aftermarket brands like Osco which are cheaper but may not last as long. The labor can be extensive depending on how difficult it is to get to each side and how rusted the bolts are. Make sure you use new gaskets when you do the work. Here's a link to help you get started: http://www.ebasicpower.com/exhaust/ .