Fuel line percolation in 1991 Volvo 740


Any ideas on how I can cheaply reduce the engine compartment temperatures. Percolation is a problem and I don’t have the time to wait around while the engine cools on hot summer days.


I seriously doubt that fuel line percolation (a.k.a. vapor lock) is your problem on a fuel injected vehicle.

What’s it doing exactly?


It has all the typical percolation [fuel starvation] symptoms after running in hot stop and go traffic. The problem is also intermitent. When the engine cools down the poblem self corrects and the engine runs fine until “the next time.” I agree, vapor lock became a thing of the past with fuel injection but apparently ethanol has allowed for a recurrence. My [non-dealer] Volvo mechanic says with our new bio fuels the alcohol is boiling at a lower temp than gas in the line, resulting in alchohol in a gaseous state passing through the injectors. He also said he’s seen more of this problem in cars over 100,000 miles. MIne has 171,000. I thought higher temps may be due to deteriorating heat sheilds. Doing things to cool the engine compartment is my idea.


What happens if you run non-alcohol based fuel in it?

Anything is possible I guess, but there are a number of things that can cause a temp-based symptom like this along with being intermittent. Coil, ignition module, fuel pump, ECT or ACT sensors, ignition switch or relays, etc. Even spark plugs or wires can come and go like this based on temperatures.

I have no idea on lowering underhood temps short of a ram-air hood scoop.
JMHO anyway.


I’ll find out about the non-alcohol based fuels when it comes out of the shop. [It was brought in on the hook on Friday] I’ll let you know what the analysis is. If it is excessive heat I’ll try wrapping the fuel line in an automotive grade heat shield wrap of some sort.