I’m gonna say something that I’ve been working on for over a year now. It will not be received positively from the community. But please, understand that I’ve been taking measurements across over 80 200s under lot of conditions. It took me a long time to even accept this as I just didn’t feel the failure was what I “wanted to believe.”
Also, don’t take what I say as gospel, I would like to be proved wrong here. It frustrate me a lot on what I believe the issue is.
What I’ve found, is the following. Let go of anything aftermarket causing fuel boiling. Just let it go, it’s not the culprit. 200s have been boiling fuel long before most things were even available for our trucks. Elevation doesn’t necessarily matter. Ambient temp doesn’t necessarily matter. Fuel type and octane equivalent levels doesn’t necessarily matter. Emissions equipment doesn’t matter. Age sometimes matters, but I’ve seen plenty of brand new, bone stock 200s boil gas when off road or towing.
Toyota uses a return style fuel system. Just like on the 4.7L, Toyota found that it was best to run the fuel pump wide open. Then uses a fuel pressure regulator to manage the fuel needed for the motor. The extra goes back to the tank. BUT!!! This is where it gets interesting. They use the extra fuel to cool various components on the top end of the motor. Fuel is a hell of a cooling liquid and Toyota uses it, along with engine oil and coolant to keep their V8s from ever over heating.
So… when you are applying a lot of load on the engine, it is going to run hotter. You are now sending hotter fuel back to the tank. After awhile, you will raise the fuel temperature of the tank to where it will boil. Fuel only needs very low 110ish°F to boil. And higher octane fuels have lower boiling points, so that isn’t helping. Detonatates higher, but boils lower. Anyway, can now boil away in the tank, but still not cause vapor lock like on old carbureted motor due to their pretty well designed pressure regulator and pumps that can still flow boil liquors good enough to never mess with a perfectly running 5.7.
I’ve plopped temp sensors in tank, in line on the send and return lines, and it pretty clear that the 150° fuel returning to the tank is raising the tank temp level. Auxiliary fuel tanks, engine bays loaded with batteries, aftermarket bumpers, skid plates, big tires, roof racks with massive RTTs, it doesn’t matter. This is a deeper problem.
So I feel from my findings building these trucks that, ugh… it pains me to say this.
Toyota F’ed up.
They put so much emphasis on keeping the engine cool, that they forgot about the stuff behind it. Toyota can put in 2 transmission coolers, one engine cooler, steering cooler (which is legit because I broke my Tacoma rack due solely to heat) but they needed to put a cooler for the fuel.
I’m heavy into other Toyota forums from BudBuilt, and the Tundra guys with 5.7s also are plentiful with fuel boiling statements. And if you didn’t know, under those trucks, it’s wide open with space, but they still boil. Because it’s not about crap around the truck, it’s about the motor and fuel system itself.
The 4.0, both single and duel VVT-I and the 3.5 bit have very little reports of boiling fuel. From tuning my own 4.0, how Toyota ran the fuel back to the tank on those, it did not have to cool as much and the way back to the tank. I personally melted a stock resin fuel tank skid on my FJ from exhaust heat. Just melted it like a grilled cheese, but NEVER boiled fuel, or head about anyone boiling fuel then. But have always heard about it from 100 series guys. In Iraq, I ran a lot of 100s and 200s with gas motors (they worked better for our needs than the diesels, that and I blew a lot of turbos and needs more reliability) we boiled fuel all the time. I just had many other things I cared about at the time.
So that’s it guys. Our precious, should be the most perfectly engineered vehicles of all time, is not perfect. Toyota should of managed fuel heat, they didn’t. I have been working on a solution, but honestly, at this point, I’d rather help everyone with knowledge than providing a future solution. We just need to cool the fuel. It’s not hard, it doesn’t hurt reliability (as I know that will be the next thing that most of us won’t be able to accept) it just needs a simple cooler in a good spot. I’ve played with the concept already, and proved that it works. What I haven’t done is made a good kit for it to be plug and play.
So that’s my story guys. On this particulate issue, we need to become Jeep and Land Rover enthusiast, and fix what the factory failed to do in the first place. It’s hard to accept, I’ve personally lost months of sleep over this.
Some extra reading on data points if you want them. I e found that under racing conditions, it’s hard to boil fuel. The reason is because most of the fuel is consumed, and air flow over the top of the motor is high. Remember, there is now factory air flow under the motor, but that’s not the problem, it’s cooling if the top end, and heat rises. High load, and no wind, that builds heat, but uses little fuel, and little cooling from air being literally rammed through the engine bay. Which is off roading or slow towing. LCDC ‘19, I watched two separate 200s with nothing more than all terrain tires boil some serious fuel. I also saw one 200 with a lift and slider boil, and a super built 200 with freaking everything boil. They all did it when off roading. Have air vents won’t help a thing, because heat rises. The air cooling only helps when air is being forced right through the grill over the top of the motor, that it, it has nothing to do with heat down low off differentials or exhaust. I personably have a Jet-Hot coated headers to muffler that cuts radiant heat over 50%. That. It advertised, that real life testing I did. Guess what, didn’t do a damn thing for fuel temps.
Best thing to mirage right now. Don’t ever open your fuel cap, even if you see fuel boiling out. Just like your radiator, pressure raises boiling points. So keep the cap on, unless you like to lower you fuel’s boiling point even lower. Then, turn your engine off. No more fuel running over a hot motor, it then cools very very quickly. Wheeling with people who s*** their 5.7s off a lot seem to never boil. Those who run in low range constantly and leave this motors running when stopping to access the trail, seem to boil much more regularly. Also, as the motor itself gets older, it runs hotter, just how it works, so while I’ve seen more sub 5,000 mile 5.7s boil fuel, it can happen more when they get up there in mileage. Another thing I’ve found it people adding aftermarket wiring to the engine room (the technical term for the fuse box) I’ve seen that play havoc with the fuel delivery and air injection systems cause the motor to run hotter, which as a side affect, boils gas.
