Cowling, Baffles and Cooling

This article collects Builder Technical Support answers on cowling, baffles and cooling.

Identifying baffle part numbers (Lycoming IO-360 and similar)

If you cannot find the part number for a specific baffle in the construction manual or on the web store, send a clear photo of the part (or the location it goes) and your engine model (e.g., IO-360, O-320) to Builder Tech Support. The baffle set varies by engine variant and accessory case, so a visual confirmation is the fastest way to get the right part number.

Radiator outlet hose looks different from the plans

If the radiator outlet hose you removed from your 912iS during prep does not look like the hose shown on Van's instruction page 50iS/U-05 (no woven cover, no shrink wrap), Rotax has shipped different hose materials over time. Confirm with Builder Tech Support before cutting - in most cases the as-shipped Rotax hose is acceptable as-is and only needs to be cut to length. Do not discard the original hose until you have confirmation.

Baffle Mods for Engine Swaps

If you are converting from one engine variant to another (for example O-360-A4A to A1F6 with a constant-speed prop), expect to modify the baffles to accommodate the prop governor oil line. Drawings for the baffle parts as-shipped are available on request, but custom baffle modifications are typically left to the builder.

Baffle Kits for Engine Variants

The baffle kit for the O-320 versus other Lycoming variants is not interchangeable. If a previous builder installed the wrong baffle kit on your RV-9A, you can request the installation instructions and engineering drawings for the correct baffle kit (e.g. BAF-320) from Tech Support to modify your assembly for proper cooling. Send your engine model and current baffle part numbers.

Rubber Baffle Seal Orientation

Rubber baffle seal pieces (for example the CB-00032 series) sometimes seem swapped between corners — a fellow builder may suggest swapping B and G, but if there is still an obvious gap on the centerline or asymmetric overlap, that points to an installation issue rather than a parts issue. Send photos to Tech Support showing all four corners.

RTV Between Baffle and Engine

Builders inspecting used engines often find liberal RTV between the baffle and engine. RTV in those interfaces is a builder/maintainer choice, not a Van's requirement. The proper sealing solution is the supplied rubber baffle seal and good fit-up. RTV is sometimes added as a field expedient where the rubber seal does not fully close a gap.

Rivet Hinge-to-Cowling Squeeze Height

On the RV-12iS, KAI37iS/U-12 and -13 call for squeezing rivets into fiberglass until the shop head HEIGHT is 1.2 of the hole diameter (not diameter). For a #40 hole at 0.098", that target is 0.118" tall. A 3-4 rivet unsqueezed at 0.170" and squeezed to 0.077" is over-squeezed by approximately 0.1". Re-read the spec carefully — height, not diameter, drives the call.

Overview

The engine cowl is one of the trickiest parts of any RV build - it sits between the rigid airframe and the rubber-mounted engine, and small mistakes show up cosmetically and on the CHT gauge. Here are the most common cowl-related questions.

Cowl baffle inlet seals are cut/torn off (RV-14A)

On the RV-14A with the EXP119 engine, the CB-00023N and CB-00023O cowl baffle inlet seals can split and tear off over time. The factory replacement is the full seal sheet. If you only need the inlet seals, contact Builder Support - we can sometimes provide digital templates so you can cut your own from rubber stock rather than ordering the full sheet.

Inlet ramp misalignment (RV-14A/IO-390)

If you're seeing a significant vertical gap between the bottom cowl air inlet and the engine air filter frame cover - more than the supplied baffle inlet seal (CB-00032N) can bridge - send Builder Support photos showing both inlet ramps with the engine and cowl in place. We've seen this often enough that there are documented fixes; we'll match yours to the right one.

Engines other than Lycoming (DeltaHawk, etc.)

Van's does not currently offer FWF support packages for non-Lycoming engines such as the DeltaHawk diesel. If you intend to install a non-supported engine, the cowl, baffle kit, and FWF integration become builder-engineered work — Van's cannot provide installation drawings or support.

RV-12iS radiator life concerns

If you've been pointed to a service difficulty report on the RV-12iS radiator separating along the bottom row of fins, contact Van's directly for the current SB or SL status. Don't rely on third-party forum reports for ongoing in-service issues - Van's publishes service bulletins and service letters as the authoritative source.

Recurring quirks

Laser-cut parts (SB-00128) - check whether your RV-10 kit is in scope
CAD files - Van's does not generally distribute CAD files for the RV-10; panel layouts are pre-designed for popular avionics suites
Cowling outlet sizing - if CHTs run hot, the cowling outlet may need enlargement; follow Van's guidance or a known-good builder mod

Fiberglass scratches and surface damage

Surface scratches in fiberglass parts (tips, fairings, cowl) are common during shipping and inventory. Minor scratches that do not penetrate the gel coat are cosmetic and will be covered by primer and paint. Deeper gouges or delamination should be photographed and sent to Builder Support to determine whether the part needs replacement or whether a documented epoxy repair is acceptable.

When to contact Builder Tech Support

For any of the above, include your builder number / serial number, the engine model, and clear photos. For baffle and cowling questions, photos of the part installed in place save several email round-trips.

Van's Tech Q&A: My Engine Runs Hot

Copied from Van's Aircraft Tech Q&A on 2026-10-01. Source: My Engine Runs Hot.

Other than the traditional “heavy wing” crisis, the most common first flight question is “My engine runs hot, what do I do?” After extracting as much pertinent info as the builder will share, usually the answer is “Nothing – keep flying.” Here’s why.

Read Lycoming Service Instruction No. 1427B.

It’s common during the first few hours of flight with a new or overhauled engine for it to run hotter than it will later when it is broken in. You need to run above 65-70% power for at least the first 2-3 hours (Lycoming say 50hrs, but the first few are the most important) to seat the rings properly, and until that’s done there is significant internal friction. Add-ons like electronic ignition, CS props, plenums, high-compression pistons etc. will exacerbate any heat problem.

Don’t worry about oil temps at or below 230F and/or CHT up to 440F or so. It is OK to run the engine at those temps for break-in; they are still below redline (245F for oil, 500 for CHT). Don’t throttle back below 70% power unless the temps reach those limits, or possibly you’ll glaze the cylinders.

Tips for initial flight tests to minimize heat problems:

Calibrate your oil temperature and CHT gauges with boiling water (212F) before you fly to make sure
they’re accurate.
It’s handy to have a Manifold Pressure gauge even on an airplane with a fixed pitch prop. If you’re relying on rpm only, you’re guessing at the power setting anytime the throttle is retarded from full. Power settings as a combination of MP and RPM can be found in the Lycoming Operator’s Manual or can be estimated by adding the RPM (in 100s) to MP (in inches). 2400rpm + 24” MP = 48, which is roughly 75% power. 45 = 65% power, so for break-in purposes you never want the RPM + MP to fall below about 46/47 (eg 2300rpm + 23” MP).
Check the plugs for correct heat rating, and the ignition timing.
Aim to do initial flights on cool days. If you must do it in Arizona in August, at least fly as early in the morning as possible. Ambient temps over 70 degrees won’t help. Early morning usually means smooth air too, another benefit. We get a lot fewer calls about hot engines in the winter.
Check the baffling. You did remember to install the inlet ramps on the upper cowl? And close all those awkward gaps around the baffles behind the spinner? And caulked all the gaps between the baffles and the engine case? Air that bypasses the cylinder fins is of no value.
Keep climbs shallow and airspeed high to maximize cooling. Do NOT climb out at 80smph. Make it more like 110-120smph minimum.
If the CHTs are low/normal, but the oil temp is high, check the Vernatherm valve to make sure it is diverting oil to the cooler properly. In addition, higher oil temps are common on angle valve and custom Lycomings that have piston oil jets installed as more heat is extracted through the oil in those engines.
If you have a CS prop, dial the rpm back to 2400 or so ASAP after takeoff, or even leave the blue knob back before t/o. Less rpm = less heat. Plus, the internal cylinder pressure will be higher, assisting ring seating.
Make sure the mixture lever on the carburetor or fuel servo really is at the full rich stop. Most carburetors will run richer at full throttle, so paradoxically the engine may run cooler at full, rather than partial, throttle. Lean only when necessary for high altitude operations, otherwise keep the mixture as rich as possible while maintaining smooth engine operation.

Van's Tech Q&A: Simulating Propeller for Fitting the Cowl

Copied from Van's Aircraft Tech Q&A on 2026-10-01. Source: Simulating Propeller for Fitting the Cowl.

In the process of building any of Van’s RV you will reach the point of fitting the cowl. The process is a bit daunting just because of its size and flexibility. A couple of things that can help are the following

DON’T install the propeller! It will simply get in the way while you are trying to install the cowl. (see the DO instructions)
DON’T install the exhaust system! It will only be in the way.
DON’T install the starter, alternator or carburetor! They will only be in the way too.
DON’T install the filtered air box! It must be fitted to the carburetor and the lower cowl after the cowl is fitted.
DON’T install the baffle kit! It will need to be fitted to the cowl after it is fitted.

What CAN I do?

1. Simulate the propeller location by the following method:

First be sure the starter ring gear is ON the engine (the toothy thing on the front)
Now locate a couple of feet of white PVC pipe that will just slip over the crankshaft lugs. (typically ¾”-1” pipe or so)
With a table saw or chop saw, cut 6 pieces of the pipe that are 2¼” in length if you are using a Sensenich or fixed pitch propeller or 2 1/8” inch length if you plan to use a constant speed propeller. Square the ends!
Now position the spinner backplate in front of the engine with it spaced ahead of the crankshaft ring gear on the PVC pipes. Ordinary hardware-store bolts can be used to hold it there. They go through the spinner bulkhead and the PVC and the starter ring gear and the crankshaft flange.
Eyeball the backplate for centering over the crankshaft and you are ready to go.

2. Follow the instructions! Here are a few things to help.

There are two different hinge types used. The hinge that attaches the cowl perimeter to the firewall is HINGE PIANO 1/8” and that is the only place you will use it. It has a .120” hinge pin (SSP-120) however, the hinge as delivered in the kit has an aluminum pin and it must be removed and replaced with the supplied steel pin (throw away all of the .120” aluminum pin). Use the replacement .120” steel pin everywhere EXCEPT for one area! In the heavily arced region (the upper third of the firewall) you CANNOT use the .120” pin (it won’t make the arc and go in or out) so we have supplied .090” for that area (SSP090). All the fairly straight sections will use the .120” steel pin.
The hinge that joins the upper and lower cowl halves together is AN257-P3 (or an equivalent MS number ending in –3). It has the .090” steel pin in it as delivered. It is used as delivered.
Fit the upper cowl first to the firewall be sure to space it back from the spinner backplate by at least 3/16” or ¼”. A little help can be had in positioning it by fixing a wooden block on the nose area of the engine that holds the front part of the cowl in the correct vertical position while you are trying to measure and mark the firewall part of the cowl for trimming.
Fit the lower cowl to both the firewall and the upper cowl.
Stand back and admire it!!

3. Now install the rest of the accessories including the carburetor and filtered air box.

4. Relax.