Ok, here's the deal:

'Sometimes' lumpy accelleration problem. ('Sometimes' the car behaves normally under hard accelleration, sometimes the power will plateau several times along the power band on the way to 5500rpm)*

*not the trail-off of power after 5500rpms normal to all N/A Maximas - I'm aware of that 1.

I have no DTC's from the ECU. 91k mi on the car.
60k mi service was performed.

I just replaced the fuel filter, thinking it may have been clogged, but the problem remains.

Then. . .

I noticed one time after I shut the car off, both the upper and lower radiator hoses were nearly collapsed, as if there were a vacuum (negative pressure) in the cooling system.

The coolant level seems fine & I have no leaks, coolant was flushed at 60k mi & I've had no problems until recently. Hoses appear to be in decent shape (x-cept 4 collapse) w/ no worn areas, damage, etc.

So, my question I guess is:

If (one or both) of the radiator hoses are collapsing under hard accelleration, could the resulting blockage & strain on the water pump cause enough load on the engine to explain the hesitation/power plateaus?

I'm considering a stainless-steel braided hose setup in hopes that if that's my problem, the S/S hoses will be more resistant to collapse.

Anyone else have this problem? -Or have any theories on what the REAL problem might be?

Btw, I haven't worked up the desire to bloody my knuckles pulling out the knock sensor to test it to see if that's the problem - n-e-1 know if you can test it without removing it from the car? I didn't get DTC on it when I pulled codes - as I understand it, the K/S DTC is only triggered in conjunction with another, anyway.

Thanks in advance.

-KWheelzSB-

 

Make sure you have the correct radiator cap on. Your cooling system should be under pressure when it's warm. When the pressure exceeds the cap/system capacity it bleeds off coolant into your reserve tank. When the motor cools down and the pressure in your cooling system goes down and eventually into a slight vacuume condition, a valve in your radiator cap should open to allow the blead off coolant to return into your radiator. This slight vacuume should be no where near enough to collapse your hoses.

 

It's weird that it happens right after you shut off the engine?

When the water/coolant cools, it "contracts" and the vacuum draws the excess coolant from the reservoir tank. This happens a while later after the engine starts to cool usually.

If the hoses are old, it may be time to change the radiator hoses although this may not necessarily solve your problem.

 

Maybe there's a blockage along the hose to the reservoir, or the reservoir itself. Check there. When you experience the hose collapsing situation, dis-connect the reservoir hose and see what happens. Be careful of the hot fluid.

DW

 

i had a problem much like that once before...radiator hoses would 'suck' themselves in. turned out it was just a bad thermostat that had stopped opening to relieve the pressure.

maybe this will solve your problem?? if so, it's an easy inexpensive fix (for once!).

 

Thanks guys, for all the great insights!

Never knew there was a relief valve built into the cap - ya learn something new every day! My cap is OEM, but the valve may have finally failed, I guess, or there is a blockage in the system somewhere, as was suggested.

-Will do some digging & update as soon as I get to the bottom of this one.

Cheers,
-K-


PS: Re- The hose collapse "after I shut the car off" -I only know the hoses are collapsed 'for sure' by viewing the engine bay, so until I can devise a way to see the hoses while the car is moving (hmmm. . .not sure I can pull that 1 off), my theory is that they are collapsing also while the car is underway - not just when idle & parked or shut down.

 

Do you know what part this was, specifically? Do you have a part #?

TIA,
-K-

 

actually, the car i was referring to was a Supra i had a few years ago (my first true car love), so i don't have any sort of part number. i'm pretty sure it's just called a thermostat. i remember picking it up at autozone for not much money (like maybe ~$20). i also put it in myself, so that means it really can't be hard.

i would try picking up a Hayne's manual or something like that. they have good info on this stuff.

 

Thanks - got a Hayne's already. I'll look into it.

Cheers,
-K-

 

Mine do that too. But i guess there just old. I didn't know that it could hurt performance though.

 

Actually, I'm not sure whether it can hurt performance or not. Still would like to know if someone knows the answer to that question:

"If (one or both) of the radiator hoses are collapsing under hard accelleration, could the resulting blockage & strain on the water pump cause enough load on the engine to explain the hesitation/power plateaus?"

TIA.

 

I'd like to know that too. I mean my car feels much better after changing ALL the o2 sensors but it still feels like it is either all or none on acceleration.

 

Here's what I've been able to determine so far:

1) The coolant reservoir tube is not blocked on either end.

2) When the engine is cool, the upper & lower radiator hoses are collapsed & remain collapsed indefinitely.* When I unscrew the radiator cap and remove it, the hoses return to normal (uncollapsed) instantly.

QUESTION:

Do you all think this means a), my radiator cap is not working correctly, or b), my hoses are fatigued & need to be replaced?

(I guess I may just need to spend the $6 on a new cap & see what happens - would rather do that than swap the hoses, only to find the problem remains)

*Correction from original post: the hoses DO NOT return to uncollapsed state after 15-20 mins, as I reported earlier.

 

So all i need to do is take the cap off? Are my hoses still bad if they collapse like that?

 

Is it possible that air is in your system?? Sounds like it. When you removed the cap, did you see anti-freeze in the radiator? Nevertheless, I would suggest doing this:

1) Replace the cap.

2) Get the air out of the system using these steps;

a) on a very very cold car, remove the newly replaced radiator cap. The radiator cap will remain off for this entire process.
b) Start the car and let the car warm up. You may want to rev the motor every so often by pushing the cables at the throttle body.
c) While you are doing this, you are watching the fluid in the radiator carefully. Top up the anti-freeze if you don't see any. The anti-freeze will remain still for quite a while until the car has warmed up and the thermostat has opened.
d) Once the flow starts, you will see it in the radiator.
e) At that point, rev the motor a few times, bubbles should start rushing past. Also, the fluid level may get low, so top it up regularly.
f) Keep doing that until you see no more bubbles. Also make sure that the anti-freeze is filled all the way up. Once the flow has started in the radiator, it may take 20-30 minutes to get all the bubbles out. The faster you rev the motor, the harder the water pump will push, and the more bubbles you will force out. I would go to like 2000-3000 rpms on the tach every so often.
g) Done. Turn off the car, replace the cap, and top up the reservoir.

Hope this helps

DW

 

Thanks for the explanation.

 

Thanks dwapenyi, for taking the time to write that up.

I didn't actually do the 60k service myself, so I guess maybe when the shop did the coolant flush, they didn't get all the air out of the cooling system.

(The coolant level inside the radiator appears normal when the engine is cold, but I'll follow the procedure you outlined & see what happens).

Best,
-K-

 

I just tried this method and i had bubbles coming out from the get go. i topped off the radiator and continued on. it warmed up fairly quick and it seems the radiator was very hot. I checked upper and lower hoses and they were hot. the fluid was actually bubbling and smoking and not once did my rad fans kick in. is this normal?

 

it's probably OK because the system is not under pressure with the cap off. Any heat generated just eveaporates.

DW

 

upon further inspection i found that i actually have a blown head gasket.

 

Umm... just to clarify, DO NOT take the cap off when the engine is HOT... unless you want to get scalding hot radiator fluid all over yourself.

 

How could you tell?

DW

 

coolant in my oil and cylinders.