Boat Engine Overheating
Overheat alarm going off? Here’s what causes overheating on outboards and inboards, and what to do right now to avoid serious damage.
Ethan, the owner and mechanic, answers the phone · Open 7 days a week
- Same / next day availability
- On-site & marina service
About This Problem
When the overheat alarm goes off, bring the engine to idle and shut it down if the temperature keeps climbing. Running hot can warp heads, burn pistons, and turn a $200 impeller into a new motor. Most overheating has a simple cause.
Temp alarm going off? Shut it down and call Ethan. He’ll tell you what to check first.
Call 786-351-5363Most Common Causes
These are the causes we find most often.
Worn or burnt impeller
The most common cause. Impellers should be changed yearly or every 100 hours.
Blocked water intake
Weeds, a bag, or barnacles over the intake starve the pump.
Stuck thermostat
Corroded thermostats stick and restrict flow.
Heat exchanger
On closed-cooled inboards, a clogged or leaking heat exchanger causes overheating and coolant loss.
Exhaust manifolds and risers
Internal corrosion blocks water flow on inboards and sterndrives.
Cracked fittings
A cracked water inlet fitting can cause an overheat on its own.
What We’ve Found on Real Jobs
From Ethan’s job log across South Florida.
Impeller never changed
A 2019 Yamaha had its first impeller change after six years and 150 hours. The owner thought it didn’t need service.
Heat exchanger
A motor losing coolant and overheating had a bad heat exchanger.
Cracked inlet fitting
A cracked water inlet fitting was the whole cause of one overheat.
High-speed overheat
An engine that only overheated at high speed was fixed and running cool again.
What You Can Check Before You Call
- Check the tell-tale stream on an outboard
- Look for anything blocking the water intake
- On inboards, check coolant level when cool
- Look for steam or water leaks around manifolds
When to Call
Don’t keep running an engine that’s overheating. Shut down, check the intake, and call. We can often fix it at your dock.
No call center. No front desk.
When You Call, the Owner Picks Up
Every call goes straight to Ethan, the owner of EG Marine Services and the mechanic who does the work. There’s no receptionist taking a message and no waiting on a callback from someone who’s never seen your boat.
Tell him what’s going on: the alarm on the display, the noise at idle, the engine that won’t turn over. Ethan knows Yamaha, Suzuki, Mercury, and the rest of what runs in South Florida inside and out, so you’ll usually get a straight answer on the first call, whether that’s something you can check yourself or a visit to your dock.
- Straight answers, not a script
- Diagnostic questions answered on the phone
- Honest advice, even when the fix is simple
- The person you talk to is the one who shows up
Ethan
Marine mechanic
Describe what the boat is doing and get a real answer from the mechanic, not a message taker.
Call Ethan: 786-351-5363Open 7 days a week
How We Fix It
Engine Overheating Repair
Impellers, thermostats, heat exchangers, coolant service, and exhaust manifolds and risers.
Learn moreCorroded Exhaust Manifolds & Risers
Overheating, rust stains, or water in the cylinders: manifolds and risers wear out.
Learn moreOutboard Not Peeing
Weak or no tell-tale stream: a clogged hose, worn impeller, or blocked intake.
Learn moreGet an Engine Overheating Repair Scheduled
Call Ethan directly786-351-5363Open 7 days a week · No call center or front desk, you talk to the person doing the work
Prefer a free quote?
Leave your number and we’ll call you back.
Frequently Asked Questions
Why does my MerCruiser overheat at idle but not at speed?
Often a stuck thermostat, a weak circulating pump, or a worn raw water impeller that can’t move enough water at low RPM. Shut it down and call before it causes damage.
Why does my boat overheat at high RPM or under load?
Usually a worn impeller, a partly blocked intake or heat exchanger, or restricted risers and manifolds. We pressure test and inspect the cooling system at your dock.
What should I do when the overheat alarm sounds?
Throttle back to idle. If the temperature doesn’t come down quickly, shut the engine off and check the intake and tell-tale.
Can I run it home slowly?
Sometimes, at idle, if the temperature stays normal. If it keeps climbing, don’t. Call for a tow or a mechanic.
How often should impellers be replaced?
Once a year or every 100 hours, whichever comes first.