Volvo C70 '99 swap B5254T with B5234T3

Fef0 · Post by **Fef0** » 19 Sep 2025, 11:36

Hi guys,
I own a stock 1999 Volvo C70 equipped with a B5254T (2.4T LPT, it's an European model) and a manual transmission.

The odometer shows only 101k km (around 63k miles) but the engine burns oil (clouds of grey smoke occasionally comes out of the exhaust whenever I downshift gears), so I guess that it has some kind of issue with piston rings and/or head gasket.

Since I'm forced to open the engine, and eventually rebuild it while I am at it, I was thinking about swap it with a B5234T3 from a '97 S70 T5 to get more power and torque.
As far as I know, the two engines should be pretty much the same, except for the obvious differences in displacement, bigger turbo and different ECU.
Is there anything else I would have to change/adapt to run the new engine? Am I forced to change the ECU or it just needs a tune? What about wiring?

Thank you for the help!

Post by **abscate** » 19 Sep 2025, 14:39

Your 97 engine won’t have vvt in the exhaust so the 99 eco will be unhappy about that. You will have to stay with the 99 ecu as it talks to the CDm and other stuff and is VIN matched

Fef0 · Post by **Fef0** » 20 Sep 2025, 02:26

Thank you very much abscate, do you think it would be just a matter of an ECU tune or I might have other problems?

What about other components? For example, is ETM electronic like in my '99? I have the infamous Magneti Marelli one

Thanks

Post by **abscate** » 20 Sep 2025, 02:39

1999 was the first year with electronic ETM. You can move the coil on plugs to the older engine and then block off the distributor hole with a cap thatVolvo sells. A tune could remove the VVT function, I don’t know a lot about that. Pcv is different on the older block but that’s some hoses to adapt fuel line attaches differently so the intake manifold amd injectir rail has to be swapped.

If you are near Turin or Rome I’ll come by for an MVS picture!

Fef0 · Post by **Fef0** » 20 Sep 2025, 03:40

Thank you for the info, unfortunately it's more work than I thought (especially for the lack of ETM which will be a PITA for sure) so for now I will try to find a newer engine, maybe a '99 or '00, but since they are so rare in the italian market it's almost impossible to find one in good condition (or even to find one in the first place)

I live in Sicily, southern part of Italy, so pretty far away from both of those cities!

Post by **scot850** » 20 Sep 2025, 08:02

I know of guys that have used newer engines in older models but not the other way around. They could do this as the block is mostly the same or still has the bolt holes that were used in older engines. The difficulty in moving to a later model is even the dashboard wiring harness is different from a -98 to that of a 99-. The cvvt solenoid on the exhaust side of the 99- engines would be difficult to remove.

The issues with your current engine are surprising at that mileage. It is more likely one of 2 issues, or both:

1) Valve stem seals have hardened and failed allowing oil to bypass down the valves into the combustion causing smoke. This is mostly seen on accelerating, slowing down and sometimes at idle, especially when cold.
2) Turbo has a blown oil seal. Again noticeable in the same way as #1)

There is one other possibility and that is the PCV system has a blockage from possibly many short trips and not enough engine oil changes. This can be tested by using a rubber/latex glove with an elastic band wrapped around it placed where the oil fill cap is. Look up rubber glove test.

I would suggest having cylinder compressions checked and let us know what those results are. They can be tested 'dry' which will give a better idea of the piston condition, and then with a small amount of oil in each cylinder to help confirm the pistons are good or the valves are bad. If the compressions improve, the issue is piston, if they don't it is valves.

Neil.

Post by **Clemens** » 20 Sep 2025, 16:52

I'd first suspect the valve stem seals or the turbo as well. Hard to believe the turbo would be bad with these little miles. My 94 T5 would smoke like hell once the turbo went bad at around 300.000 km.

The valve stem seals harden up with time. This is likely after these years. Check for it by letting the car idle for about 3-5 minutes and then floor the gas pedal. If it smokes violently, the valve stem seals are likely bad. Also, bad valve stem seals cause a cloud of smoke after startup im the morning.

I think your LPT should have a 13T Turbo. If that is correct and you need a spare turbo, I think I have a 13T in my garage that I bought mislabeled as a 15G.

Fef0 · Post by **Fef0** » 20 Sep 2025, 17:17

Hi guys, thank you very much for the help.

I had my turbo checked and they told me that it is still ok.
I will try the glove test just because I'm pretty sure that the previous owners didn't check the PCV in the entire lifetime of this car. The smoke only comes out of the exhaust, not the oil cap nor the dipstick, do you believe that the PCV might be the issue?

For sure I will also have a compression test done ASAP as scot850 suggested.

Again, thank you for the help guys!

Post by **matthew1** » 20 Sep 2025, 17:22

abscate wrote: ↑20 Sep 2025, 02:39 1999 was the first year with electronic ETM.

Keep in mind he has a Euro spec, and they got things a year before we did. Not that it makes a difference in this case.

@Fef0, I took my son to Sicily in 2017. We stayed in Aci Trezza. The first 4 of these are getting to Sicily, but the rest are Aci Trezza, Mt Etna. You can see Aci Castello in the background of one. viewtopic.php?p=598728#p598728 Excellent places, excellent people.

Sorry about your engine. Post back here if/when you decide to dig into it and repair rings or valves.

Fef0 · Post by **Fef0** » 20 Sep 2025, 18:58

matthew1 wrote: ↑20 Sep 2025, 17:22
abscate wrote: ↑20 Sep 2025, 02:39 1999 was the first year with electronic ETM.
Keep in mind he has a Euro spec, and they got things a year before we did. Not that it makes a difference in this case.

@Fef0, I took my son to Sicily in 2017. We stayed in Aci Trezza. The first 4 of these are getting to Sicily, but the rest are Aci Trezza, Mt Etna. You can see Aci Castello in the background of one. viewtopic.php?p=598728#p598728 Excellent places, excellent people.

Sorry about your engine. Post back here if/when you decide to dig into it and repair rings or valves.

I live less than 30min away from Aci Trezza, it's truly an amazing place even for people born and raised here in Sicily, same thing for Mt Etna!

I will keep you guys updated, thank you!