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Clean or replace a Flame trap on B23 - B230 series engines

For B20 engines click HERE


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New Flametrap

Do you know where the Flame trap is located on your Volvo ? Probably not, I guess.. You better find out soon, it could save you lots of problems and money later !!

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All the used Volvos I bought in the past or inspected for others had flametrap problems, most had completely blocked flametraps. Recently, I inspected a Volvo 740 owned by a lady in our village and yes ....... there was an old type flametrap completely blocked. The problem was that the owner of the car had the Volvo serviced by a local garage not familiar with Volvos and this flametrap was probably the original one from new. Luckily, I keep some spares for our own fleet, and I was able to fix the problem for her and probably saved her an expensive seal replacement job.

On older Volvos like my 1968 Amazon (B18) crankcase pressure is released to the air through an oil trap on the side of the engine block. On later engines the gasses are re-circulated to the intake manifold to avoid release in the atmosphere.

The flametrap is installed in that circulating hose on the 200 series Volvos. The flametrap itself is a little disc (top photo) of the size of a NZ$2 coin. The old type flametraps were of the metal wound type as shown in the top photo, however they were replaced about 10 years ago by a plastic type with larger openings and which is a lot easier to clean. In particular the older type flametraps collected oil and other dirt and in the end plugging the flametrap completely.

A blocked flametrap means crankcase pressure build-up and forces oil past the seals causing oil leaks so common with the older Volvos or even blowing out seals completely (I speak from experience) and losing most of your engine oil !!

Replacing the flametrap is just regular preventive maintenance. On 1976-80 models you'll find the trap at the cam cover. On 1981-88 models you'll find it under the intake manifold on the side of the block. Access is not easy, but by following the hoses as shown on the photo of my 1988 240GLT engine, you will find it.

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To simplify access to the flame trap, you could remove the bellows from the throttle housing. Now you can much more easily reach the flame trap and you can also clean the throttle plate. However, if you know what you are doing, it is possible to remove the flametrap unit without removing the bellows. It is always a hassle putting the bellows back on properly.

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of the air/fuel unit
Location of flametrap
bellows removed
Flametrap pulled
off the oil seperator

The flametrap housing can be pulled off the oil separator and the hoses, a big one and a small one, can be pulled off the flametrap housing. The plastic piece is probably very brittle. Be careful when removing this piece, it is very easy to crack the "Y" piece that attaches to a vacuum hose. Use a pair of needle-nose pliers and be gentle! It can be done without removing any other equipment. Make sure that all the hoses and the nipple on the manifold are not blocked. On 1988 and later models the flame trap is nestled in between the cylinder head and intake manifold, it is easily accessed from above. Also some people have re-located the flame trap that way for better access and I think that even sells a special kit for that.

A flametrap costs around NZ$10 and is available from your Volvo Service Dealer. Do NOT clean the old metal wound flametrap but REPLACE it by a new plastic one. Replacement of engine seals means removing the gearbox and would cost around NZ$500.

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When you are doing this job, also ensure that all hoses and nipples are clean and not blocked. Inspect all hoses for cracks or split hoses. Any problems with hoses could unsettle your engine or create starting problems. I found this split hose on a bypass valve when servicing the flametrap on my 240GLT. 

I had my fair share of crankcase pressure build-up on my old 1982 Volvo 244GLT over the years because of a blockage that the (Volvo) garage couldn't find. After many seal replacements I found the culprit myself. Fed-up with the ongoing problem, I removed the intake manifold and fuel injection unit to access the oil separator mounted on the side of the B23E block and found part of an old metal wound type flametrap pushed in the exit (top) of the oil separator, it was stuck and blocked circulation completely, thereby causing pressure build-up in the crankcase which blew the seals out when revving the engine !! Somebody had knowingly done that. Maybe the previous owner or his mechanic. This problem had cost me over NZ$1000 at that time (10 years ago).

Jim Hekker
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