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Thread: Is it the infamous hot soak......

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    Is it the infamous hot soak......

    So I drove home from work last night (10 miles), got home turned the van off and went into the house to get ready to take the girlfriend to dinner....20 minutes or so).... As we get in the car and start it up, it would crank, start and then die. So, I start it and give it some gas and hold steady at 2-3k...... then it was ok.

    What does that sound like it could be? I just took it to a mechanic friend of mine to go through it and it checked out great. Curious if it's the hot soak problem ive heard about and if so what is that and how do i cure it?

    P.S. this is the first time it has happened.

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    Re: Is it the infamous hot soak......

    You could either replace the fuel pressure regulator for a 1989 Toyota Van regulator, or put up with it. I chose to just put up with it for now. Won't hurt anything. They, supposedly solved the hot soak issues in the 1989 models by using a higher pressure regulator.

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    Re: Is it the infamous hot soak......

    Oh, OK. So basically it's not hurting anything?

    What is causing this and does my vans symptoms even sound like a hot soak problem or something else?

    Thanks guys!

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    Re: Is it the infamous hot soak......

    It sounds like it. There is a sequence of events and certain conditions that lead up to hot soak. It's hard to accurately duplicate these conditions for testing, so chasing down and proving the problem can be difficult.

    I will attempt to explain the issue as I understand it. Since the van is a mid-engine vehicle the engine compartment cannot be vented on top (smoke and noxious fumes in the passenger compartment isn't a good thing). So as a result the engine is sitting under a sealed metal dome. When you shut off the engine, since the cooling fan is run by the water pump, the coolant circulation and the air ventilation go away. Since heat rises it gets trapped there in the dome and cannot escape. If it's a hot day and/or if you've been driving it hard (like going up a steep hill or freeway driving) then there's even more heat getting trapped there. To complicate things, the fuel rail, injectors, pulsation damper, and FPR (Fuel Pressure Regulator) sit right above the exhaust manifold and are covered by the upper half of the intake manifold.

    The extreme heat that's trapped there soaks into the fuel rail and depending on the quality of gasoline and the pressure in the rail, the gasoline may boil. The result is expansion and vaporization.......otherwise known as a vapor lock condition. Since there is still pressure in the fuel rail, the regulator will not allow more fuel into the rail until pressure is reduced. The only way vapor/pressure can escape is through the injectors (when you are trying to start). Of course vapor isn't dense like liquid, so there's not enough energy being delivered for your engine to start or run correctly. As the vapor/pressure escapes into the manifold new fuel trickles into the hot rail and immediately vaporizes. When vaporization occurs, volume increases exponentially (expansion) and that keeps the pressure up. This in turn prevents sufficient amounts of fuel from entering the rail. Once started, keeping the engine RPM's up helps because the injectors will vent vapor/pressure faster and allow more new gas to enter the rail. The faster the cool gas flows into the rail, the quicker the rail cools. Once the rail is cool enough to hold liquid gasoline the problem disappears and the van runs normal again.

    Because this involves boiling and vaporization, there is a direct correlation between the quality of gasoline and this problem. Back in the 80s this wasn't such an issue because gasoline had a higher boiling temp. Todays gasoline has lots of additives (such as ethanol) and this can significantly lower the boiling point. You can minimize this problem by staying away from the gas that says it has a high percentage of alcohol/ethanol but this option may not be available. It's my belief that gasoline is becoming standardized and brand name doesn't matter much anymore.

    So this leaves you 2 other options:

    1. Increase fuel pressure in the fuel rail (higher pressure = higher boiling temp)

    2. Provide ventilation to your engine compartment after shut-down

    I'm not crazy about option #1 because increased pressure = more stress on injectors and other fuel system components (IMO this is more of a safety issue). If and when a fuel system leak occurs, more fuel will leak and your fire danger goes up. That being said, there is an easy way to automatically increase your fuel pressure for only a couple of minutes after start-up. IMO, the benefit of this is questionable because you will only be increasing pressure AFTER the fuel has been boiled. In other words this will minimize the effects of hot soak, but will not prevent it from happening.

    There is also a way to permanently increase pressure in the fuel rail, and this makes more sense to me because it's more likely to prevent the problem from occurring. Of course this benefit is off-set by decreased safety.......and that's not to be taken lightly. Fuel leaks in the fuel rail area are not uncommon and several vans have gone up in smoke (sometimes taking other property with them).

    Before changes are made, one should understand how the system works. Our FPRs (Fuel Pressure Regulators) have 2 output pressures. When vacuum is applied to the FPR diaphragm it will put out around 30 psi. When no vacuum is present, it will put out around 40 psi. There is a temperature switch on the engine coolant filler neck (vans that came with factory AC). This is a simple on/off switch that's triggered by coolant temp. The switch is normally open but when coolant temp hits 230 deg F it closes and grounds the wire going to it. That wire is attached to the ECU (Electronic Controlled Unit). Each time the van is started, the ECU monitors that circuit and if it detects a ground condition it activates the EFI VSV (Electronic Fuel Injection Vacuum Switching Valve) for a period of about 2 minutes. When the EFI VSV is activated, it shuts off vacuum to the FPR and vents the FPR diaphragm to atmosphere. With no vacuum, the FPR holds pressure at around 40 psi. After about 2 minutes, the ECU turns off the EFI VSV, vacuum returns to the FPR, and pressure returns to around 30 psi.

    The existence of this system tells me that Toyota realized the potential for heat soak, but miscalculated the activation temp (of course the changing fuel market is partly to blame). Later on when heat soak became a bigger issue Toyota issued a service bulletin (TSB #E020). Part of that bulletin requires mechanics to replace the 230 deg F switch with a much much lower temp 140 deg F switch. The lower temp switches were only available for this service bulletin campaign (see PDF file attached to this post) and are now NLA (No Longer Available).

    If you think about it, the normal operating temp of the engine is about 185 - 210 F so this means the new switch will activate the "pressure up" mode of the fuel injection system almost every time the van is started (unless the van has had over an hr to cool). Because of this, I think it's reasonable to assume it wouldn't hurt for the "pressure up" mode to be activated on every start (including cold ones). This can be easily achieved by simply cutting the wire off of this sensor and attaching it to ground.

    To permanently increase pressure, there are several ways this can be done, but probably the simplest method would be to disconnect the vacuum line from the FPR and plug it to prevent a vacuum leak. I wouldn't put a cap on the FPR port because you'd want the diaphragm in there to breath. Again, I don't recommend this, but I'm providing the info to help create a better understanding of these issues.

    Personally, the remedy I like best is the "ventilation after shut-down" method. I'm using this method (and this method only) on my van and I've been happy with it. A side benefit to this ventilation is increased life span of rubber seals, rubber hoses, and other sensitive parts (due to reduced temps in the engine compartment). I've heard other guys talk about opening their hoods each time they stop or using computer fans and ducts to ventilate small amounts of cool air into this area, and I don't disagree with the success of such methods, but who wants to have a super heated and/or smelly cabin on a hot day? As for the small fans and ducts, there's already limited space here and access to key areas is already tough enough. That's why I chose to install electric cooling fans on my radiator. I built a shroud and installed (2) 10" high output electric fans on the back-side (engine side) of my radiator. I rigged them up to be thermostatically controlled and wired direct to the battery (so they have power all the time). I got an adjustable t-stat with a submersible probe, put the probe into the extra 16mm port near the front of the head, and set the t-stat to come on at 200 deg F. Now whenever the coolant temp is 200 deg F or above, the fans will run (doesn't matter if the ignition is on or off). This has worked out great for me and completely solved the heat soak issue.

    The fans do come on and run (on and off for about 20 - 30 min after shut down), but they eventually stop and I've always been able to restart the van easily.

    I just realized this is a pretty long winded post so I'll stop here. If anybody is interested in pictures or more details, please ask and I'll be happy to answer questions and/or post pics/schematics. Tim

    PS: Installing an 89 FPR will help, but only slightly. I probably wouldn't replace an earlier version just for this benefit, but if it needed replacement anyhow, I'd definitely go with the 89 FPR. FWIW, normal operating pressure of the earlier FPR's is 27-31 psi and the "pressure-up" mode is 33-38 psi. 89 FPR's normal operating pressure is 30-33 psi & "pressure-up" mode is 38-44 psi.

    This thread has a bit more related information: http://www.toyotavantech.com/forum/s...tached-diagram
    Attached Images Attached Images

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    Re: Is it the infamous hot soak......

    WOW...... Now that was a response!!!

    Very very useful info Tim and definitely helped me understand what "heat soak" is. However, one last question.... Can "heat soak" hurt your engine?

    It has only happened once and I run 91 octane from either chevron or shell.

    Thanks as always guys!

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    Re: Is it the infamous hot soak......

    Lol, I'm surprised you made it through all that. Sometimes I get started and just can't stop . Heat soak is hard on your starter and embarrassing when witnessed by others......other than that it's just a nuisance. Over time, the excessive heat in the engine compartment will harden rubber and plastic parts. Tim

    BTW, high octane gas won't help. If your engine doesn't ping on the 87 octane stuff, then more octane is just a waste of money.

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    Re: Is it the infamous hot soak......

    Quote Originally Posted by timsrv View Post
    BTW, high octane gas won't help. If your engine doesn't ping on the 87 octane stuff, then more octane is just a waste of money.
    Holy crap balls!! I thought I read somewhere that your van will run better and get better gas mileage on 91? Please tell me I haven't been wasting my money.....

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    Re: Is it the infamous hot soak......

    Octane ratings effect pre-detonation, which can be an issue on high performance engines.............but we're talking about boiling points here. So unless you've done something to effect compression ratios, 87 octane should be fine for your van. I'd be a little weary of the no-name discount gas..........especially if has ethanol. Usually they will display a sign that says 10% ethanol or whatever. If you can run it and have no problems, then fine. If however you get heat soak issues more on one gas then another I'd avoid the gas that gives you problems. I'd also monitor gas mileage and avoid fuel that consistently gives you poor MPGs. Tim

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    Re: Is it the infamous hot soak......

    Awesome, looks like im back to 87

    Thanks Tim!

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    Re: Is it the infamous hot soak......

    hey, I've tried both the solutions that Tim "detailed". Grounding the temp sensor heloed a little but didn't completely solve the problem. Ventilation solved the problem. I kept the stock cooling fan and fan clutch and installed an additional fan on the front of the radiator and hooked up a thermostat probe to the (return) fuel line right above the fuel rail. Set the thermostat to activate the fan at a temperautre such that the fan does not run during engine operation (except under extreme conditions like very slow ascent or idling in very hot conditions) but kicks on after shut down when the temperature climbs in the engine compartment. This was a relatively simple modification and worked awesome

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    Re: Is it the infamous hot soak......

    If someone could post photos of the fan install I would appreciate it.

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    Re: Is it the infamous hot soak......

    well I should really try to take some pictures - maybe next weekend?

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    Re: Is it the infamous hot soak......

    Here's a bunch of pics of my fan set-up. I plan on writing a detailed article but haven't gotten around to it yet.

    The shroud is made of 22 ga galvanized sheet metal and soldered at the seams with 50/50 solder. It is made to perfectly fit (2) 10" electric fans.













    The adjustable thermostat I'm using to make my fans turn off and on is a capillary type with a 1/4" sensor probe on the end. To make the transition from the 1/4" sensor to 16mm X 1.5 pitch threads (the size of the extra unused port), I purchased a brass adaptor at the local hardware store. It originally was 3/8"mpt on one end and 1/4" compression on the other (these are readily available). I also purchased a 16mm X 1.5 die and simply chased the slightly larger 3/8" threads to convert to metric. The larger size 3/8 pipe thread was almost too big to chase without turning in a lathe, but with a little effort and patience this can be done by hand with only a vice and hand threading tools. After chasing, the new metric threads are perfect. You cannot even tell it was ever a standard 3/8 pipe thread . See the t-stat and modified brass adaptor below:








    Here's some links to thermostats controls: http://www.amazon.com/Flex---lite-31...3160624&sr=8-6 http://www.amazon.com/Flex---lite-31...3160624&sr=8-1

    The one in the black box is basically the same thermostat but it has a relay and some diodes added. I like this one because the relay protects the t-stat. The other cool part is it gives you multiple options for triggering fans. One of the posts hooks to your AC and turns the fans on anytime you're running AC, another post is for a manual override switch on the dash. I have this control installed on one of my vans and it's easier and cleaner than building one from individual components.

    I see that Flex-A-Lite now has a variable speed fan control that uses a thermistor type probe with wires. It is a metal probe and could most likely be immersed in the coolant (most accurate way to trigger fans). Tim

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    Heat soak

    Suddenly I have heat soak issues (vapour lock) on my 89 4wd. My experience with VW and Porsche tells me pressure has gone down in the fuel rail which allows the gas to boil. Given that 89 FPRs are higher pressure and somewhat free of this issue I am going to assume my FPR is bad. On the German cars the problem was almost always a bad fuel check valve (often part of the fuel pump). We had work arounds for Porsche 911s with their really high pressure and metal lines involving an in-line check valve unit (cheap) to avoid fuel pump replacement (costly). Do our vans have a check valve that might be the culprit or is it just the FPR that keeps the pressure up when the engine is off? I can open the engine hatch and bleed heat when I park etc but I think a new FPR is the way to go - right? Unless there is a check valve trick someone knows about?????
    Arghhh. Har Har Har. It's a pirate's life for me!

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    Re: Is it the infamous hot soak......

    Yes, it could be low fuel pressure, but it could also be the result of cheap gasoline. I'm not sure about where you're at, but in some places they introduce a "winter blend" gasoline around this time of year. This "winter blend" often has an even lower boiling point than the "summer" gasoline and could be at least partly to blame for your problem. I would recommend testing your fuel system with a pressure gauge before spending time and money on a fuel pressure regulator. FWIW, I have replaced the FPR on a 4wd van before and I can tell you that job really sucks. 2wd vans are manageable but the 4wd vans are very challenging. I'm a seasoned mechanic and I had to use about every trick and swear word in my vocabulary .

    Here's a write-up I just posted on Testing the fuel system / Replacing fuel pressure regulator. Tim

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    Re: Is it the infamous hot soak......

    Thanks Tim.
    I guess this is just another darn job I should have done when I did the injectors and had the intake manifold off.
    Man, I missed the boat on that one and left the hose of death, the TPS and the FPR untouched.
    I deserve a beating!
    Chevron Gas. Canada. West Coast near Bellingham Washington.
    Arghhh. Har Har Har. It's a pirate's life for me!

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    Electric Fan Set-Ups - Hot Soak Re-Revisited 2013

    Living in Texas, I'm looking to make my van Hot Soak proof. It seems an Electric Fan setup is the only reliable way & the extra cooling capabilities might help a bit during summer (which is year round here) too.

    I did a general Google search & there are plenty of other classic vehicles that are struggling with modern ethanol gasoline too. Likewise, electric fan setups appear to be the standard practice.

    Tim did a write-up on his thermostat set-up before but I've yet to see where & how y'all are putting your electric fans.

    Tim did mention that the thermostats are a bit dodgy & need to be replaced every few years. Has anyone found an ultra reliable Thermostat?

    Does anyone have any photos, part numbers, wiring diagrams, etc... I don't want to be the guy who can't start his vehicle on the Ferry this summer.


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    Re: Electric Fan Set-Ups - Hot Soak Re-Revisited 2013

    I ran the set-up shown above for about 5 years & it worked great. The only bad part was this style thermostat seems to fail every 2 or 3 years. I had thermostat failure twice & both times resulted in an overheat (before I realized what was happening and turned on the manual override switch). The 1st time it happened I thought it was a fluke, but the 2nd time really annoyed me so I replaced with a Flex-a-Lite #31165 variable speed control. The thermistor sense probe used with this controller is also 1/4" diameter so it fits using the same adapter I used before. I was very happy with the performance of the variable speed control but my van was put out of commission by a reckless/uninsured/unlicensed motorist before I had a chance to test long term reliability.

    I plan on fixing this van, so eventually it will be back on the road for more testing. Here's some pics of the installed Flex-a-Lite control:





    Although not directly related to the fan shroud/fans, here is another add-on/upgrade that helps direct air flow up and into the radiator/engine compartment when cruising. I made this "scoop" out of galvanized sheet metal flashing. There is a noticeable improvement in cooling when cruising at highway speeds with the AC on:















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    Re: Electric Fan Set-Ups - Hot Soak Re-Revisited 2013

    Hi Tim,
    I am really interested in your awsome repair for the heat soak problem. After a hilarious scene at the local country club where I picked up my son, trying to restart on a hill with a car parked close to my front bumper, I had to back up the hill to get out. Spinning tires, a roaring engine, in lots of looks of disapproval had my son and I in stitches of laughter for a half hour after! But, I guess I need to see if I can cool the engine better so I'd like to create your setup. Did you make measurements or does it have to be a custom creation? This is my DD so I would need to turn it around fairly quickly. I would be happy to make a donation, etc, for plan's or guidance.
    Thanks,
    John

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    Re: Electric Fan Set-Ups - Hot Soak Re-Revisited 2013

    The scoop was something I "threw" together in an afternoon with materials I already had on hand. I just cut it with tin-snips then bent it over itself for strength. Basically I just bent a little, held it up to the van, bent & cut some more, held it up to the van & repeated until I was satisfied. The shroud took more time as I soldered at the joints and used a heavier sheet metal. I didn't write down any dimensions, I just used an old radiator I had laying around and simply made the shroud to fit.

    Any sheet metal shop could do this pretty quick. Just take them your radiator and print some pics from this thread for them. In hind sight I made mine more complicated than it needed to be. I wouldn't have had to make a relief for the transmission cooling hose if I had not made the shroud so deep. Trestlehed (member here) had one made that is thinner and simpler. I would guess it works as good as mine. He probably has pics posted somewhere. Tim

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