Buying a 1998 Maxum 2100 SR – What to Watch For?

[MAXMAXUM]

Hi everyone,

this Saturday I’m going to look at a 1998 Maxum 2100 SR with a 5.7L MerCruiser EFI (300 hp).
The engine block was replaced in 2020, so the previous owner invested several thousand euros in the engine and drive overhaul.

I’d really appreciate your advice on what weaknesses I should be watching out for with this model.

One of my main concerns is the fuel tank – since it can’t really be inspected easily, is a leaking/rusty tank just a matter of time on a 1998 boat?

The seller also mentioned that a “carb cleaning” is needed, but this is an EFI engine – so that confused me a bit.
In addition, he said the oil pan gasket needs to be replaced. Is that something that can realistically be done with the engine in place, or does it require pulling the motor?

Thanks a lot for your help!
Best regards
Max

[mmwjr]

I would approach this with great caution. The sell has given conflicting information about it being a carburetor vs fuel injected. The standard engine would have been carburetor. Now he may have repowered with a newer Vortec long block which is the EFI block but installed a carburetor intake manifold, I did this when I repowered in 2016. Count the number of bolts on the intake, if it’s 12 it is not an Vortec which has 8 bolts. Another caution is it needs a carburetor cleaning, get him to do it! In many cases I have heard this line and in the end the buyer gets stuck with a bad engine that needs major work as the seller knows it’s bad but uses that line to cover up why it’s running bad. The engine needs to be removed to fix the oil pan gasket. A fuel tank of this age can go bad but can also last much longer. The main thing that shortens their life is if high bilge water is left in the boat for extended periods of time.

[MAXMAXUM]

Thanks a lot for your detailed answer, that really helps me.

I’m not sure the seller will actually do the carburetor cleaning before selling – it feels like he just wants to put in as little work as possible and move the boat at the end of the season.

Why would someone put a carburetor intake on an EFI block? Is there any advantage to that, or is it simply because the original EFI intake didn’t fit the long block?

This boat also has a wakeboard tower, so I assume it has been run hard. But can a repowered block already be worn out again after only 5 years?

The leaking oil pan gasket makes me wonder if it could also be a sign of high crankcase pressure (which could point to the end of the engine).

During a sea trial, what else should I watch out for besides exhaust sound, smoke, and power? I don’t think I can do a compression test on all cylinders on site – should I still ask for one, as well as the carb cleaning?

I also have the invoices from the shop that did the repower. Would it make sense to reach out to them directly to verify what exactly was done?

Link to picture of engine (Looks similar to another 300hp EFI i looked for comparison but without the cap ober intake)

https://s1.directupload.eu/images/250915/uacntizy.jpg

[shrew]

I wouldn't bother reaching out to the shop unless you know someone there. The seller is the shop's customer, not you. You have no idea what their relationship is, but I assure you the mechanic is going to strongly support the quality of his work.

I don't trust difficult to verify explanations for common and sometimes significant issues. "It just needs a carb cleaning".......famous last words.

[MAXMAXUM]

Thank you so much for your input. Great to have this Maxum Forum.

So, I reached out to the seller (who is very nice and friendly) and asked about the symptoms. I specifically asked what the mentioned “cleaning” was about. The seller said the fuel amount is electronically regulated, but he suspects the injectors might be contaminated with rust or similar debris. He already checked and flushed the fuel lines.

The symptom is: when going WOT (full throttle quickly), the engine kind of bogs down / stumbles (to me it sounds like too much air and not enough fuel catching up). Under normal acceleration and cruising it seems to run fine.

He also told me he had already bought a large ultrasonic cleaning tank to clean the injectors, but never got around to it. In the meantime now, he upgraded to a bigger, more modern Maxum.

Does that sound like a common/solvable issue? Any ideas what else it could be?

This was starting 2 years after the full rebuild, he actually brought it in the shop to get a look at this. They changed: sensor TPS, Ignition finger and cap, spark plugs and fuel filter in mid of 2022 for that reason (did not improve anything).

I asked about bringing the boat for a checkup to the mechanic who rebuild the engine, but he was not very motivated to do so and recommended another mechanic (they put a too tight belt on the rebuild engine and the impellerpump and servopump needed replacement because of noise/bending later).

There were no intake changes, TPS Sensor is only on the EFI Model and was not changed later.

Link to picture of engine:
https://s1.directupload.eu/images/250915/uacntizy.jpg

Best regards
Max

[MAXMAXUM]

Thank you so much for your input. Great to have this Maxum Forum.

So, I reached out to the seller (who is very nice and friendly) and asked about the symptoms. I specifically asked what the mentioned “cleaning” was about. The seller said the fuel amount is electronically regulated, but he suspects the injectors might be contaminated with rust or similar debris.

The symptom is: when going WOT (full throttle quickly), the engine kind of bogs down / stumbles (to me it sounds like too much air and not enough fuel catching up). Under normal acceleration and cruising it seems to run fine.

He also told me he had already bought a large ultrasonic cleaning tank to clean the injectors, but never got around to it. In the meantime now, he upgraded to a bigger, more modern Maxum.

Does that sound like a common/solvable issue? Any ideas what else it could be?

This was starting 2 years after the full rebuild, he actually brought it in the shop to get a look at this. They changed: sensor TPS, Ignition finger and cap, spark plugs and fuel filter in mid of 2022 for that reason (did not improve anything and fed up of shop after another expesive bill).

So he basically also told me that he was not very satisfied with the mechanic, because the belt model put on was too tight so he needed a new impellerpump and later had to change the servopump himself because the old one got bent.



Best regards
Max

[MAXMAXUM]

So, I reached out to the seller and asked about the symptoms. I specifically asked what the mentioned “cleaning” was about. The seller said the fuel amount is electronically regulated, but he suspects the injectors might be contaminated with rust or similar debris.

The symptom is: when going WOT (full throttle quickly), the engine kind of bogs down / stumbles (to me it sounds like too much air and not enough fuel catching up). Under normal acceleration and cruising it seems to run fine.

He also mentioned that he had already bought a large ultrasonic cleaning tank to clean the injectors, but never got around to it, since he upgraded to a bigger, more modern Maxum.

Another point: he wasn’t very satisfied with the company that did the engine overhaul. About two years later he went back to them because of this exact problem. They changed spark plugs, distributor cap, rotor, and the fuel filter – but without improvement. Because of that, when I suggested having them do a full check-up at my expense, he wasn’t too motivated.

Important detail: the intake is still the same with TPS sensor (only with EFI, no change was made during the overhaul).

Does that sound like a common/solvable issue? Any ideas what else it could be? He also cleaned the Fuel lines himself.

[mmwjr]

Impossible for us to know how difficult and expensive the fix will be over the internet. Does it currently run and if so will he allow a sea trail? This would give you some idea of how bad it runs. Pictures of the engine for us may help. Depending on the asking price which IMO would have to be no more than half the market value to cover potential repairs it may be too much of a gamble.

[MAXMAXUM]

Yes, we will do the sea trial on saturday.
It seems to run great but when you really punch it quick WOT it stubles down. I'll keep you updated.

Best regards
Max

[mmwjr]

That appears to be the early throttle body fuel injection system. Do you have a picture with the flame arrestor removed? If not can you get one. The symptom you describe is what happens when the accelerator valve is bad on a carburetor. On fuel injection it’s probably due to the injectors being dirty or worn nozzles.

[MAXMAXUM]

I bought the 1997 Maxum with a 5.7L MerCruiser EFI yesterday (it was listed as 1998). I’m really excited for the upcoming season.

I’ve already done some test runs – overall it runs fine, though there are a few small issues (idle still a bit high, occasional backfire at full throttle). I’m currently checking the old fuel, filters, and ignition system step by step.

Looking forward to tips and experiences from other Maxum or MerCruiser owners – and hopefully I’ll be able to give something back to the community as I learn more.

I added 4 bootles Mannol 9202 to ~80 Liters of fuel and idle went down from 1800 to 1000 after 30 minutes of driving.

Best regards from Berlin
Maximilian

[mmwjr]

Congratulations! Did you get a picture with the flame arrestor removed?

[MAXMAXUM]

Not yet. I will keep you updated. I think the fuel cleaning additiv with a strong mixture of >1 bottle per 30L already worked very well. I will update when you when the stumble and backfire at fast WOT is gone. Today on the short drive i did not go WOT but already reached >55 km/h on plane with the 4 Blade Prop.

The Mercruiser plastic with decal on top of the Engine/ throttlebody is missing. Is it possible to order a replacement?

[mmwjr]

Not to my knowledge but if you have the engine serial number you can look it up here and see if you can find one.

https://www.marineengine.com/parts/m...iAAEgJMvfD_BwE