This page has questions raised by Perkins owners about issues with their engines. Thanks to Robert Aston, we also have scanned copies of some original Perkins manuals: (Caution, these are 1.5 to 6.6 MB files and may take a while to load.)

Perkins Operators Manual
Perkins Shop Manual
Perkins 4-108 Parts List (Incomplete)



Was interested to see Michal's email of July 16. Fyi, about a month ago, after several emails/phone calls -- I sent him about 60 pages from the Perkins Manual and Shop Manual (mine was the $60 version, purchased in 1996). Given all his questions, perhaps we can get him to signup for I36 Assoc. membership! I suggested this, so we'll see if he senses a benefit that he can't "tap" free of the Internet. I'll take a crack at a few of his latest questions; and presumably others will also.

My overheating problem now seems to be sorted out. It was primarily due to a clogged bronze "L" fitting ( at the end of what Michael described as a reverse letter "U"). Beyond this, also had the heat exchanger "boiled", impeller replaced and a number of new major coolent hoses installed. Now runs at 162-165 deg., which is where it should be with my thermostat. Will be heading up to delta this Thursday, via overnight at Benecia, with ultimate destination being Piper Slough (Mike Fitz-Gerald's place -- this is a TYC event, but Mike, as you probably recall, owns Shenanigans and is a member of the I36 Assoc). A good test for the engine!

Having just resolved the overheating problem -- thought I'd comment on a couple of your open questions:

(1) Re the "reversed letter "U" pipe you mentioned. If this taps off of the heat exchanger, which it does on mine --and, if it can't be "cleaned-up, you might contact List Marine in Sausalito. They just installed either a new one -- or did a super clean-up of the old one on my boat last week (I didn't ask at the time, but when the bill comes, I'll know!). (Incidentally -- my overheating problem was primarily due to the "L" bronze pipe coming off the aft portion of this pipe being clogged. Also had the heat exchanger "boiled" out, which contributed somewhat to the overheat problem.)

(2) According to my mechanic at List Marine -- there are no sacrifical zincs in the engine per se. The only one is in the heat exchanger (I change this every year -- In most cases, the "pencil zinc's" (available at W. Marine) have to be cut down about 1/2 inch with a hack saw to fit. When changing, recommended procedure is also to open "cap" at end of the heat exchanger, and clean out resedue build-up.

(3) Running temp is, in part a function of the thermostat you have (varies); and, to a lesser extent, the size of the prop. My 4-108 has a 165 degree thermo, and drives a 12/8 3 blade propeller. Normal operating temp -- when all is going well -- is between 162 and 168 degrees. (In recent months -- temp gradually increased to 180 deg F, and enroute back from Benecia last weekend -- rose to 190 deg. Hence, the recent work by List Marine. It's now running at the temp it should! Not an engine problem -- all in the coolant sytem infrastructure).

(4) Cruising RPM is very much a function of the transmission and the propeller size/pitch. I have a 1:1 transmission with a 12/8 3 blade -- my max. "effective" RPM is around 2200 - 2300. Best way to establish proper "cruising" speed, my mechanic says -- is to use a GPS on calm water -- and gradually increase the RPM, as you monitor the "ground speed". At some point (about 1950 RPM on my boat), the "over the ground" speed recorded by the GPS will not increase -- to go beyond this simply uses fuel and overly exercises the engine. Again, I've been told that 90% of the max RPM you're engine/prop will deliver is often appropriate for ongoing cruising. (The owner's manuel references to RPM are not particularly relevant -- each boat/prop/transmission configuration will determine appropriate cruising and max. RPM).

(5) Oil pressure is also "boat" sensitive -- but most 4-108's tend to operate between 50 and 60 psi, depending on Rpm and operating temp.

(6) Perkins (and most "English" built engines") tend to have some ongoing oil leaks -- often around the oil fill pipe, the raw water pump and the rear engine seals. I've been lead to understand that if these are minor "showings" of oil -- not measurable leaks, that is not unusual -- and no major concern. Just be sure to check your oil level on a regular basis. (I change my oil & oil filter every 70-80 hrs, and rarely have to add oil inbetween). As an aside -- if the oil level, per the "dip stick" begins to rise -- and there is a "milky" appearance -- shut the engine down immediately. It is indicative of water getting into the crank case, usually due to a malfunctioning raw water pump, but it can also come from other sources. Corrective action is to immediately flush the crank case -- with a minimum of 3 or 4 oil/filter changes -- after correcting the basic problem (e.g., raw water pump).

Hope some of this proves helpful --- and, when time permits, don't forget to join the I-36 Association (application forms on our Web site). I think you'll find it very worthwile as the owner of what will prove, if it hasn't already, to be a design and sailing classic.

Don Henderson