CONTINUOUSWAVE

Q1: should the replacement of a fuel tank [of unspecified capacity] on a 1986 OUTRAGE [of unspecified length] with a fuel tank of only 25-gallons capacity be considered a "red flag", that is, a boat that should not be purchased?

BACK STORY
I may buy a one-owner 1986 Outrage [of unspecified length] with a 2012 Mercury 150-HP engine [of unspecified model]. During a 2012 refurbishment the factory fuel tank [of unspecified capacity] was replaced with a 25-gallon fuel tank. The boat has only been used on New England lakes so apparently the [limited] fuel tank capacity wasn't a concern for the present owners.

Q2: Outrage what?

Q3: Which model?

[A replacement fuel tank of only 25-gallons] will scare off a lot of buyers, but that is not hard to correct.

Expect to spend $1,500 to $3,500 to have a appropriate fuel tank fabricated and installed. Factor that into the offer price.

To answer your question, readers will need to know the length of the OUTRAGE and the capacity of the original fuel tank.

PREDICTING RANGE
Assuming the 150-HP engine is a modern four-stroke-power-cycle engine, and assuming the engine when running at cruise speed of 25-MPH will be producing about 100-HP, and assuming its fuel consumption will be about 9-GPH, and assuming a fuel tank of 25-gallon capacity for the purpose of range would be derated by 15-percent to only 21.25-gallons, then the small fuel tank would permit a running time of only about 2.4-hours, or a range (at 25-MPH) of barely 60-miles.

As for the current boat set up allowing only a 60-mile range and if that constitutes a "red flag", that will depend on your intended use of the 1986 OUTRAGE of unspecified model and length. Then on that basis, you must give more information:

Q4: what is your intended use for the 1986 OUTRAGE of unspecified length whose fuel tank capacity is only 25-gallons?

Also, if the present fuel tank is in excellent condition and its only fault is small capacity, you could easily modify the fuel system to have a second fuel tank that was on-deck and had a capacity of over 20-gallons. That would essentially double the range of the boat, as you could operate from the on-deck tank until it was out of fuel, then switch to the main tank. That accommodation would be much less expensive that tearing out the small fuel tank and having a new tank fabricated. A suitable fuel tank would be the Moeller 24-gallon on-deck fuel tank. See

The MOELLER 24-gallon White On-deck Fuel Tank for Boston Whaler Boats
https://continuouswave.com/forum/viewto ... f=4&t=5807

ASIDE: when I was cruising on my 1986 REVENGE 20 in the Pacific northwest on the inside passage behind Vancouver Island, to supplement the boat's 77-gallon fuel tank I also carried an on-deck fuel tank of about 12-gallons. Having some extra fuel on board was reassuring, as in some parts of the two-weeks- underway trip the availability of gasoline fuel was limited.