{"id":494,"date":"2026-09-09T14:14:53","date_gmt":"2026-09-09T14:14:53","guid":{"rendered":"https:\/\/oayachtservice.com\/knowledgebase\/?post_type=docs&#038;p=494"},"modified":"2026-09-09T14:14:54","modified_gmt":"2026-09-09T14:14:54","password":"","slug":"exhaust-overheat-probes-cleaning-maintenance-intervals","status":"publish","type":"docs","link":"https:\/\/oayachtservice.com\/knowledgebase\/?docs=exhaust-overheat-probes-cleaning-maintenance-intervals","title":{"rendered":"Exhaust Overheat Probes Cleaning &amp; Maintenance Intervals"},"content":{"rendered":"\n<h2 class=\"wp-block-heading\"><a>1. Background<\/a><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Most yacht diesels use a wet exhaust. Hot exhaust gas leaves the turbocharger, and raw (sea) water that has already passed through the engine&#8217;s heat exchangers is injected into the exhaust at the mixing elbow or injection ring. From that point aft, the exhaust gas is cooled enough to run through rubber hose and fiberglass mufflers to the transom.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">That arrangement depends entirely on water flow. If raw-water flow stops or is reduced \u2014 a blocked sea strainer, a failed impeller, a collapsed hose, a scaled injection ring, or a fouled heat exchanger \u2014 the exhaust temperature downstream of the injection point climbs within seconds. Exhaust hose softens and delaminates, mufflers can crack or melt, and in the worst case the hose fails and hot exhaust enters the engine room.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The exhaust overheat probe (also called a wet exhaust temperature sensor, exhaust high-temperature alarm, or exhaust water temperature sender) exists to catch that condition. It is a temperature sensor mounted in the wet exhaust, normally within the first section of hose or pipe after the injection point, and it reports to the vessel monitoring or alarm system (for example B\u00f6ning, Maretron, Aqualarm, or the builder&#8217;s alarm panel). When the temperature at the probe exceeds the set point \u2014 typically in the region of 70\u201395 \u00b0C (160\u2013200 \u00b0F), depending on the installation \u2014 an alarm sounds at the helm.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Two things are worth being clear about:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>The overheat probe is not an engine sensor.<\/strong> It does not measure combustion or turbocharger temperature. The engine&#8217;s own exhaust gas temperature (EGT) sensors, where fitted, sit on the dry side before the turbo and report to the engine controller. The overheat probe protects the exhaust system, not the engine.<\/li>\n\n\n\n<li><strong>The alarm is the last line of defense, not a maintenance reminder.<\/strong> By the time it sounds, the raw-water problem already exists. The probe&#8217;s job is to give the crew enough warning to shut down before the hose is damaged.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><a>2. Why probes foul<\/a><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The probe tip sits in an environment that alternates between hot exhaust gas and salt water spray, and it fouls in three ways.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Scale.<\/strong> Raw water flashing to steam at the injection point leaves mineral scale (calcium and magnesium carbonates) and salt crystals on every surface, including the probe sheath. Scale is an insulator. A scaled probe responds slowly and reads low, which delays the alarm exactly when it is needed.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Soot and carbon.<\/strong> Diesel combustion deposits carbon throughout the exhaust path. Low-load running, extended idling, and poor fuel quality accelerate it. On the probe, carbon builds into a hard glaze that has the same insulating effect as scale.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Corrosion.<\/strong> Salt, heat, and moisture attack the probe sheath, the mounting boss, the sealing washer, and the wiring connector. A corroded connector produces intermittent or false readings; a corroded sheath eventually cracks, lets moisture into the element, and the sender fails outright.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The practical consequences are false or nuisance alarms, an alarm that fails to sound during a real overheat, and \u2014 with enough build-up or corrosion \u2014 a damaged sender that must be replaced rather than cleaned.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><a>3. Symptoms that indicate attention is needed<\/a><\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><td>Symptom<\/td><td>Likely cause<\/td><td>Action<\/td><\/tr><\/thead><tbody><tr><td>Overheat alarm at start-up or intermittently at steady cruise, water flow at the outlet normal<\/td><td>Fouled probe, corroded connector, or failing sender<\/td><td>Inspect and clean probe and connector; test; replace if reading is still erratic<\/td><\/tr><tr><td>Overheat alarm with reduced water or steam at the exhaust outlet<\/td><td>Real raw-water restriction<\/td><td>Stop the engine. Check strainer, impeller, and hoses before restarting<\/td><\/tr><tr><td>Displayed exhaust temperature reads noticeably lower than a known-good sister engine at the same load<\/td><td>Scaled probe reading low<\/td><td>Clean probe; if reading does not recover, replace<\/td><\/tr><tr><td>Displayed temperature frozen, dropping to zero, or jumping<\/td><td>Connector, wiring, or sender failure<\/td><td>Check connector and wiring; replace sender<\/td><\/tr><tr><td>Alarm never sounds during function test<\/td><td>Failed sender, wiring fault, or alarm system fault<\/td><td>Trace and correct before the vessel sails<\/td><\/tr><tr><td>White or green deposits at the probe boss, salt tracks on the hose<\/td><td>Leak at the probe seal<\/td><td>Reseal or replace the sealing washer; inspect boss for corrosion<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><a>4. Cleaning procedure<\/a><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Who:<\/strong> Vessel engineer, or ECYG as part of scheduled service. No special tools are required beyond a suitable socket or wrench for the probe body.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Time:<\/strong> About 30\u201345 minutes per probe including soaking.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><a>4.1 Preparation<\/a><\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Engine stopped and cooled. Isolate the start circuit.<\/li>\n\n\n\n<li>Note the probe location, cable routing, and the alarm set point on the monitoring system before disturbing anything.<\/li>\n\n\n\n<li>Photograph the probe and connector in place.<\/li>\n<\/ol>\n\n\n\n<h3 class=\"wp-block-heading\"><a>4.2 Removal<\/a><\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Disconnect the cable at the connector. Inspect the pins for green or white corrosion, moisture, and loose crimps.<\/li>\n\n\n\n<li>Remove the probe from its boss with the correct size socket or wrench on the hex body. Do not grip the sheath or the cable. If the probe is seized, apply penetrating oil and allow time; do not force it \u2014 a snapped probe in a fiberglass or bronze boss becomes a much larger job.<\/li>\n\n\n\n<li>Remove and discard the sealing washer or O-ring.<\/li>\n<\/ol>\n\n\n\n<h3 class=\"wp-block-heading\"><a>4.3 Inspection<\/a><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Inspect the sheath before cleaning and decide whether cleaning is worthwhile:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Clean:<\/strong> light scale or powdery soot, sheath straight and intact, connector serviceable.<\/li>\n\n\n\n<li><strong>Replace:<\/strong> cracked, pitted, or thinned sheath; cable insulation hardened, cracked, or chafed through; connector body corroded beyond cleaning; or a probe that has already been cleaned once and still read incorrectly. Overheat probes are inexpensive relative to an exhaust hose; when in doubt, replace.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\"><a>4.4 Cleaning<\/a><\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Descale.<\/strong> Soak the probe tip in a mild acidic descaler. White vinegar (5% acetic acid) is effective and safe on stainless sheaths; a marine-grade descaler such as Barnacle Buster or Rydlyme, diluted per the label, works faster. Soak 15\u201330 minutes, longer for heavy scale. Do not submerge the connector or cable entry.<\/li>\n\n\n\n<li><strong>Remove soot.<\/strong> After descaling, wipe the sheath with a lint-free cloth and, if needed, a soft nylon or brass brush. Isopropyl alcohol or a mild solvent-dampened cloth will lift remaining carbon film.<\/li>\n\n\n\n<li><strong>What not to do.<\/strong> Never use a wire wheel, abrasive paper, sandblasting, a scraper, or a grinder. The sheath is thin-walled; any damage changes the thermal response and shortens its life. Never bend the sheath to straighten it. Never use hydrochloric (muriatic) acid \u2014 it attacks stainless and the element inside.<\/li>\n\n\n\n<li><strong>Rinse and dry.<\/strong> Rinse thoroughly in fresh water to neutralize the descaler, and dry completely.<\/li>\n\n\n\n<li><strong>Clean the connector.<\/strong> Electrical contact cleaner on the pins, then a light coat of dielectric grease on reassembly. Replace the connector if the pins are pitted or the locking tab is broken.<\/li>\n\n\n\n<li><strong>Clean the boss.<\/strong> Chase the threads in the boss and wipe out scale from the seat so the new washer seals.<\/li>\n<\/ol>\n\n\n\n<h3 class=\"wp-block-heading\"><a>4.5 Testing<\/a><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Before reinstalling, confirm the probe and alarm work together:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Reconnect the probe to its cable with the probe out of the exhaust.<\/li>\n\n\n\n<li>Heat the tip in hot water. For most alarm probes, water just off the boil (95\u2013100 \u00b0C \/ 200\u2013212 \u00b0F) will exceed the set point; for a temperature-reading sender, compare the displayed value against a thermometer in the same water.<\/li>\n\n\n\n<li>Confirm the alarm sounds at the helm and, where a display is fitted, that the reading tracks the thermometer within a few degrees.<\/li>\n\n\n\n<li>Let the tip cool and confirm the alarm clears and the reading returns to ambient.<\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">A probe that does not alarm, or reads more than about 5 \u00b0C (10 \u00b0F) off the thermometer, is replaced.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><a>4.6 Reinstallation<\/a><\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Fit a new sealing washer or O-ring. Apply a thin film of high-temperature anti-seize to the threads only, not the tip.<\/li>\n\n\n\n<li>Install and tighten to snug plus a quarter turn, or per the manufacturer&#8217;s torque if specified. Over-tightening cracks fiberglass bosses and distorts bronze ones.<\/li>\n\n\n\n<li>Reconnect the cable, secure it on its original clips clear of hot surfaces and chafe points.<\/li>\n\n\n\n<li>Run the engine and check for exhaust or water leaks at the boss, then confirm the monitoring system shows a sensible reading at idle and at cruise.<\/li>\n\n\n\n<li>Log the work: date, engine hours, condition found, whether cleaned or replaced, and test result.<\/li>\n<\/ol>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><a>5. Cleaning intervals<\/a><\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><td>Interval<\/td><td>Task<\/td><\/tr><\/thead><tbody><tr><td>Every run<\/td><td>Glance at the exhaust outlets \u2014 steady water flow, no steam. Note the displayed exhaust temperature where fitted and compare with the other engine.<\/td><\/tr><tr><td>Monthly or 50 hours<\/td><td>Visual check of the probe boss and connector for salt tracks, corrosion, or chafe.<\/td><\/tr><tr><td>Annually or 500 hours, whichever first<\/td><td>Remove, inspect, descale, clean, and function-test every overheat probe (mains and generators). Do this together with the mixing elbow \/ injection ring inspection, since the elbow is off and the same scale is present.<\/td><\/tr><tr><td>Every 2 years or 1,000 hours<\/td><td>Replace probes regardless of condition on vessels that operate mostly in warm salt water or do significant low-load running.<\/td><\/tr><tr><td>Condition-based<\/td><td>Any overheat alarm, any nuisance alarm, or any erratic reading \u2014 inspect and test before the next run. Any real overheat event \u2014 inspect the probe and the first section of exhaust hose for heat damage before returning to service.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Shorten the annual interval to six months for vessels that spend most of their time in the tropics, run generators for long periods at light load, or have shown heavy scale at a previous cleaning.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><a>6. Related items serviced at the same time<\/a><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Because the overheat probe protects the wet exhaust, it makes sense to service the rest of the wet side while it is out:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Mixing elbow \/ injection ring<\/strong> \u2014 remove, inspect internally, descale the injection ports, replace on condition. A partially blocked ring is the most common root cause of a real overheat.<\/li>\n\n\n\n<li><strong>Exhaust hose<\/strong> \u2014 check the first section after the injection point for softening, bulging, cracking, or heat discoloration. Heat-damaged hose is replaced, not monitored.<\/li>\n\n\n\n<li><strong>Hose clamps<\/strong> \u2014 retorque; replace corroded clamps with 316 stainless.<\/li>\n\n\n\n<li><strong>Raw-water system<\/strong> \u2014 strainer, impeller, and hose condition, since these are what cause the overheat in the first place.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"><a>7. Operating practices that reduce fouling<\/a><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Avoid extended idling and prolonged running below the engine&#8217;s minimum load band. Where low-load running is unavoidable, follow it with a period at cruise load to clear the exhaust path.<\/li>\n\n\n\n<li>Keep sea strainers clean and replace impellers on schedule.<\/li>\n\n\n\n<li>Never silence an overheat alarm or raise its set point. An alarm is a stop-and-investigate event.<\/li>\n\n\n\n<li>Keep a written record of every alarm, even if no cause was found; a pattern of nuisance alarms is usually a fouled probe waiting to be cleaned.<\/li>\n<\/ul>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\"><strong>Need Assistance?<\/strong><\/p>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\">For technical support, warranty assistance, parts, or to schedule service:<\/p>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\"><strong>Ocean Alexander Yacht Service<br><\/strong>East Coast Yacht Group<br>2955 W State Road 84 Fort Lauderdale FL, 33312<br>954-530-2033<br><\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter is-resized\"><img decoding=\"async\" src=\"https:\/\/s.w.org\/images\/core\/emoji\/17.0.2\/svg\/1f310.svg\" alt=\"\ud83c\udf10\" style=\"width:42px;height:auto\"\/><\/figure>\n<\/div>\n\n\n<p class=\"has-text-align-center wp-block-paragraph\"><a href=\"http:\/\/www.oayachtservice.com\/\"><strong>oayachtservice.com<\/strong><\/a><\/p>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\">Follow us for maintenance tips, technical updates, and service announcements:<br><a href=\"https:\/\/www.instagram.com\/eastcoastyachtgroup\/\">&nbsp;<strong>Instagram<\/strong><\/a><\/p>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\"><em>This article is part of the Ocean Alexander Yacht Service Knowledge Base. Information is provided for general guidance and should not replace the applicable Owner\u2019s Manual or service procedures.<\/em><\/p>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\">\u00a9 Ocean Alexander Yacht Service \u2013 East Coast Yacht Group, Inc.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>1. Background Most yacht diesels use a wet exhaust. Hot exhaust gas leaves the turbocharger, and raw (sea) water that has already passed through the engine&#8217;s heat exchangers is injected into the exhaust at the mixing elbow or injection ring. From that point aft, the exhaust gas is cooled enough to run through rubber hose &#8230; <a title=\"Exhaust Overheat Probes Cleaning &amp; Maintenance Intervals\" class=\"read-more\" href=\"https:\/\/oayachtservice.com\/knowledgebase\/?docs=exhaust-overheat-probes-cleaning-maintenance-intervals\" aria-label=\"Read more about Exhaust Overheat Probes Cleaning &amp; Maintenance Intervals\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"doc_category":[10],"doc_tag":[],"class_list":["post-494","docs","type-docs","status-publish","hentry","doc_category-mechanical-2"],"year_month":"2026-09","word_count":1739,"total_views":0,"reactions":{"happy":0,"normal":0,"sad":0},"author_info":{"name":"admin","author_nicename":"oaadmin","author_url":"https:\/\/oayachtservice.com\/knowledgebase\/?author=1"},"doc_category_info":[{"term_name":"Mechanical","term_url":"https:\/\/oayachtservice.com\/knowledgebase\/?doc_category=mechanical-2"}],"doc_tag_info":[],"_links":{"self":[{"href":"https:\/\/oayachtservice.com\/knowledgebase\/index.php?rest_route=\/wp\/v2\/docs\/494","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/oayachtservice.com\/knowledgebase\/index.php?rest_route=\/wp\/v2\/docs"}],"about":[{"href":"https:\/\/oayachtservice.com\/knowledgebase\/index.php?rest_route=\/wp\/v2\/types\/docs"}],"author":[{"embeddable":true,"href":"https:\/\/oayachtservice.com\/knowledgebase\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/oayachtservice.com\/knowledgebase\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=494"}],"version-history":[{"count":1,"href":"https:\/\/oayachtservice.com\/knowledgebase\/index.php?rest_route=\/wp\/v2\/docs\/494\/revisions"}],"predecessor-version":[{"id":495,"href":"https:\/\/oayachtservice.com\/knowledgebase\/index.php?rest_route=\/wp\/v2\/docs\/494\/revisions\/495"}],"wp:attachment":[{"href":"https:\/\/oayachtservice.com\/knowledgebase\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=494"}],"wp:term":[{"taxonomy":"doc_category","embeddable":true,"href":"https:\/\/oayachtservice.com\/knowledgebase\/index.php?rest_route=%2Fwp%2Fv2%2Fdoc_category&post=494"},{"taxonomy":"doc_tag","embeddable":true,"href":"https:\/\/oayachtservice.com\/knowledgebase\/index.php?rest_route=%2Fwp%2Fv2%2Fdoc_tag&post=494"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}