2001 Heat soak and aftermarket header advice.

My XJ has been on the back burner for a while now and just recently got to getting it back to trail ready status. One thing that has continued to plague it is the infamous heat soak issue(or at least I think that is what it is).

I live near Vancouver and on hot days(anywhere from 28c-36c) it simply will not start back up when hot. If I drive 20 minutes, it gets to temp and I turn the engine off(or even accidentally stall) it will not start even seconds after the engine stopped. I have to wait about a half hour until it cools down, then it will start. It otherwise runs great.

So far I have put new 4 hole bosch injectors in, put a new intake heatshield on, wrapped injectors, installed hood vents, replaced coil pack with a viper coil pack and new wires. I thought the hood vents would do the trick but apparently not.

One thing I did do, though not to try and fix the heatsoak issue, was try a cheapie ebay stainless header a while back. Of course the flange warped on me and it will no longer seal properly so I took it off(my ebay parts buying lesson), but one thing I do remember now is that I never experienced any heatsoak issues when it was on. Once I put the cast iron OEM manifolds back on the heatsoak returned. So I am wondering if the cast iron makes that much of a difference in underhood temps here. If I am thinking right I was considering getting a quality aftermarket header and just wanted to see if that makes sense. I can afford it, and at some point I plan to stroke this motor so it is not exactly wasted. I was looking at the banks torque tube header or possibly the pacesetter ceramic armor coated. Any input is appreciated.

Your stock manifold isn't the culprit.

Something else like a sensor would be my guess.

Only thing that fixed it for me was a timer to let the electric fan run after shutdown

The reason that the stainless steel headers helped is because stainless steel is a very poor conductor of heat whereas cast steel has very good thermal conductivity. Even when accounting for the reduced wall thickness of the stainless header, it will still radiate less heat. The polished or near polished surface of the stainless headers will help reduce heat conduction to the engine bay as well.

You could consider having your OE cast headers thermally coated. That will reduce the amount of heat transmitted to the engine bay by the exhaust manifold considerably. Could coat other parts of the exhaust as well.

Also, you may want to consider putting a heat reflective sleeve on the fuel line going to the rail. The incoming fuel line gets bathed in exhaust heat.

I read another thread where a person applied a sheet of DEI reflect-a-cool to the underside of the intake manifold.

maxbraketorque said:

The reason that the stainless steel headers helped is because stainless steel is a very poor conductor of heat whereas cast steel has very good thermal conductivity. Even when accounting for the reduced wall thickness of the stainless header, it will still radiate less heat. The polished or near polished surface of the stainless headers will help reduce heat conduction to the engine bay as well.

You could consider having your OE cast headers thermally coated. That will reduce the amount of heat transmitted to the engine bay by the exhaust manifold considerably. Could coat other parts of the exhaust as well.

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Yep.

Either ceramic coated or stainless will make a difference. If you noticed the difference in the past then odds are good this will help in the future.

I would not recommend header wraps however. The heat those keep inside does not work out well for a vehicle that gets driven any kind of distance. A quarter mile at a time is one thing. A few hours on the trail is another matter entirely.

Get one of these:
https://www.amazon.com/Mestart-OBDI...child=1&keywords=elm327&qid=1598161171&sr=8-8

And download Torque lite on your phone. You can set it up to watch live stream data from all the input sensors. I'll say it too. The stock cast manifolds are NOT your culprit. I live where it gets hot too, and I don't have vapor lock issues. It's actually very, VERY rare to have vapor lock on fuel injected vehicles. I'd be suspicious of the intake temperature sensor or the engine coolant temperature sensor. My 1988 Rx7 had a bad problem of not wanting to start when the engine got hot. Turned out that the wires for the coolant temp sensor had come loose out of the connector. I couldn't see it since they were pushed into the loom, so it looked like it made good contact. Unfortunately, to diagnose that ECU I had to back probe the connectors with a multimeter and paper clips. Now, since yours is OBD2, it will give you a check engine light if any of the sensors read outside of their prescribed 0.5-4.5 volt ranges. However, if it's not reading outside those ranges and just not reading properly (which can happen) you can have a no-start condition still.

Also, you have a separate coolant temp sensor for the ECU and one for the gauge. So your gauge might be spot on, but the one giving info to the ECU could be out to lunch.

Agreen said:

Get one of these:
https://www.amazon.com/Mestart-OBDI...child=1&keywords=elm327&qid=1598161171&sr=8-8

And download Torque lite on your phone. You can set it up to watch live stream data from all the input sensors. I'll say it too. The stock cast manifolds are NOT your culprit. I live where it gets hot too, and I don't have vapor lock issues. It's actually very, VERY rare to have vapor lock on fuel injected vehicles. I'd be suspicious of the intake temperature sensor or the engine coolant temperature sensor. My 1988 Rx7 had a bad problem of not wanting to start when the engine got hot. Turned out that the wires for the coolant temp sensor had come loose out of the connector. I couldn't see it since they were pushed into the loom, so it looked like it made good contact. Unfortunately, to diagnose that ECU I had to back probe the connectors with a multimeter and paper clips. Now, since yours is OBD2, it will give you a check engine light if any of the sensors read outside of their prescribed 0.5-4.5 volt ranges. However, if it's not reading outside those ranges and just not reading properly (which can happen) you can have a no-start condition still.

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I appreciate the input. I have been tackling this for years now. I have owned an ELM device since they came out and purchased torque pro years ago, I have looked at the live data many times now and see nothing out of the ordinary.

Also, vapor lock/heat soak is a very common issue on 2000-2001 XJs with the two pre-cats.....so much so that Jeep issued a TSB and a "fix" for it. I've even had someone with another 2001 come up to me randomly in a Home Depot parking lot to ask if I had a solution for it because he saw my 2001.

I get it could still be a sensor issue, but why does this only happen when it is really hot out? Why doesn't it ever happen in spring or fall? If it was a coolant temp sensor reading incorrectly then wouldn't it be an issue every time the engine got to temp? Also why did the problem disappear with a different header installed?

This isn't just confirmation bias either, please keep the suggestions coming. If a header is not my solution I still want to fix this problem, as I said I have been at this for a long time now. One thing I have not tried is the fan timer as suggested above, I've read a number of people have had success with that.

I kinda follow these heat soak threads when they come up.
I own a '00 with CA Emissions.
I don't have this problem. I don't know why. But am thankful.
I did not have it when I had the old kind of beat up heat shield on the intake manifold with the stock injectors.
Did not appear when I replace the heat shield with a brand new one and upgraded to brand new 4 hole injectors.
Oh and I just did that cause I figured the original ones had about 150K on them and just
needed to go.
The front dual cat ended up causing a P0432 down the road. Never a problem before or after I replaced that with the rest of the exhaust because it needed replacing anyway.
I mention all this just to kinda explain where my Jeep is at.
Anyway in my travels have read the usual stuff about this problem.
But came across this:

https://www.jeepforum.com/forum/f11/heat-soak-fix-not-what-you-may-think-2975897/

http://jeep.blackonyx.net/pdfs/jcss.pdf

To frank with you this is over my head. But it is not the usual rhetoric that you read about this problem.
Maybe it will help.

The only way I can see vapor lock being an issue is if the fuel rail loses all pressure and stays vented. Have you checked fuel pressure after shutting it off? If it drops off fairly quick, it's either a leaky injector (which you said you have changed) or a bad fuel pump check valve.

If it really is vapor lock, have you tried putting a heat sleeve on the fuel line that goes under the intake?

Agreen said:

Also, you have a separate coolant temp sensor for the ECU and one for the gauge. So your gauge might be spot on, but the one giving info to the ECU could be out to lunch.

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Not on a +97 model.

I too doubt its heat soak. Even though my 01 was a pile of crap I would run my stop and go 6 hour mail route on 100 degree August days and with the injector heat shield removed it would still start. It would cough and sputter and run rough until I revved it up a few time and ran some cool fuel through the injectors but I would start and stop it several times a day. And that was with it running hot because of a plugged radiator and the cracked head. With all your improvements you really shouldn't have any heat soak issue. Computers aren't always right, have you verified sensor readings with and old fashioned multi meter? Tps would be where I would start, also switch out cps if you have an extra!

biztyke said:

M ..... drive 20 minutes, it gets to temp and I turn the engine off(or even accidentally stall) it will not start even seconds after the engine stopped. I have to wait about a half hour until it cools down, then it will start. It otherwise runs great.

So far I have put new 4 hole bosch injectors in, put a new intake heatshield on, wrapped injectors, installed hood vents, replaced coil pack with a viper coil pack and new wires. I thought the hood vents would do the trick but apparently not.

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The engine should easily re-start right after shutdown or after a few moments. I would suspect a thermally stressed OBD engine sensor, and would tested the running fuel pressure and the check valve leak down.

An ELK-960 e-fan timer is low cost and will be beneficial.

Either do the timer mod or add a manual switch to get control of your E fan— its the only thing that solved my heat soak issues on my 96

My 2000 has heat soak too but that one still stars, coughs and spits for 30 seconds but still starts

Believe it or not I have a 97 lincoln continental that has the exact same heat soak issue — run that one in the summer and shut it off for 10 minutes without the hood open and it won’t run right either

maxbraketorque said:

You could consider having your OE cast headers thermally coated. That will reduce the amount of heat transmitted to the engine bay by the exhaust manifold considerably. Could coat other parts of the exhaust as well.

Also, you may want to consider putting a heat reflective sleeve on the fuel line going to the rail. The incoming fuel line gets bathed in exhaust heat.

I read another thread where a person applied a sheet of DEI reflect-a-cool to the underside of the intake manifold.

Click to expand...

Great ideas! This might help my buddy's over heating issue.

I would probably look at a Doug Thorley header. They are ceramic coated, and well built.

Thanks for all the advice. I do agree that it is odd to not start immediately after the engine stopped, I wouldn't think there would be time for full on vapor lock to set in. That said I would also think if it was a heat induced sensor issue then why would it run just fine for as long as I want it to, then not run immediately after the engine stops? Once I wait the half hour or so, when it just starts getting to catch it will sputter, cough and backfire a bit then finally catch and run ok again.

I think I am gonna do the additional mods suggested here because i think they would all be beneficial regardless, but I am still thinking of getting a header.

To bad it isn't an earlier model with fuel rail return, then you could wire a switch to the FP relay to cycle in cool fuel.

Out if curiosity, have you checked for fuel pressure or spark when the no-start occurs? Maybe I have missed where you said it. During a hard no-start condition, you're in the best position to troubleshoot. Check fuel, spark, and compression.