Volvo 850 10v to 20v Conversion.

[2ndGenVolvos]

Hi everyone.

I've got a 1996 Volvo 850 wagon that I just bought. Its got a B5252S engine (10 valve) and it burns oil and there is air in the coolant system. I took the thermostat out and its gone bad so I'm going to replace that and hope that fixes the coolant issues. (it has actually got the original thermostat from 1996)

My dad is a Volvo Mechanic at our local dealership, used to work for Volvo Canada, where he trained other mechanics and has a vast knowledge of these cars. He thinks we should be able to do this modification fairly straightforwardly and that it'll just take a lot of work to get it done. He's been working on and with Volvo cars since the early 1990s.

However, instead of fixing what we believe is the valve stem seals that are causing the engine to burn oil. But instead of repairing the 10v head, we're toying with the idea of converting the head to a 20v.

I've got a couple of questions about the feasibility of actually, successfully achieving this. Firstly, has anyone successfully done this? From what we understand, I'd most likely need to replace the intake and exhaust manifolds and the wiring harness. But would I need to replace the Fenix 5.2 ECU for Bosch Jettronick ECU?

Thank you to anyone who reads and responds,
I'd be happy to update this thread once we actually get started on the project if there is any interest in that.

[454cid]

My 96 20v uses a Motronic 4.4.

[xanthefin]

You maybe want check if 20V pistons has some extra cuts for 4 valves to prevent them hitting them but i can be wrong on this.

[misha]

It will never run properly if it would run at all.
Not just wiring....ALL sensors are different including engine management.

It's way more cheaper and less headache to just rebuild 10v head or put in a used 10v engine.

[abscate]

Or swap in a 20V engine if you want the power! I think the turbo swap is feasible too, for the monkey wrencher

[2ndGenVolvos]

My 96 20v uses a Motronic 4.4.

Do all the 96 and onward cars use Motronic 4.4? Or specifically 96?

[2ndGenVolvos]

Or swap in a 20V engine if you want the power! I think the turbo swap is feasible too, for the monkey wrencher

I wanted to see if the conversion was possible. A swap is a lot of work but if its the best option I might just go for it. I know where I can get an entire 20v 850 for $900 CAD

[2ndGenVolvos]

It will never run properly if it would run at all.
Not just wiring....ALL sensors are different including engine management.

It's way more cheaper and less headache to just rebuild 10v head or put in a used 10v engine.

Hmm interesting. And lets say I did convert all the sensors, would it run properly then? Or would it still have problems?

[2ndGenVolvos]

You maybe want check if 20V pistons has some extra cuts for 4 valves to prevent them hitting them but i can be wrong on this.

Well I'd assume I'd need to replace the pistons anyway if they're bad enough from the oil burning. Who knows whats actually going on inside the engine. It might just be more sensible to swap out the motor.

[scot850]

What mileage is on the current engine? If is is fairly low mileage it may be the cheapest to have the head rebuilt if you and your Dad can do the strip and rebuild. You will need a machine shop to plain the head and have the head rebuilt with new seals. But you could probably do that for around $1000-1200 or less as it is a 10V motor.

Yes you can buy a $900 car with a motor in it but how good is that motor?

You can compression test your existing motor to see what the compressions are like. Your Dad will know how to do that.

Neil.