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S70 T5 Vapor-lock when Hot

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

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S70 T5 Vapor-lock when Hot

Post by VolvoAffair » Thu Jul 18, 2019 10:04 am


Recently experiencing vapor lock when the temps are high. Typically, I just have to wait for things to cool off––but this is increasingly taking upwards of 6 hours.

Thoughts, comments, recommendations?

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Re: S70 T5 Vapor-lock when Hot

Post by vovo850 » Thu Jul 18, 2019 12:51 pm

In the carb days we would add a wooden clothespin to the fuel line.
Add a spacer to the carb, insulate the fuel line.
Some would add a electric fuel pump to help.
Which leads me to say that seems really odd, is your fuel pump good?
Because I never heard of vapor lock in a fuel injected engine.

Edit to add I should have added fuel relay, it may be going bad, getting hot and failing. It also would not allow a restart until it cools off. Might be closer to a vapor lock symptom as well. That is fairly easy to test, just swap the relay out.

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Re: S70 T5 Vapor-lock when Hot

Post by erikv11 » Thu Jul 18, 2019 4:37 pm

What he said - it's not vapor lock. Start by testing the fuel pump relay (jumper it), then the fuel pump.

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Re: S70 T5 Vapor-lock when Hot

Post by bmdubya1198 » Thu Jul 18, 2019 4:41 pm

I've heard of these symptoms in 240s, but never a P80. Is your fuel pump running? What's your fuel pressure at idle?

+1 on the fuel pump relay, those are common failure items. It's very possible that it's overheating and failing.

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