Bypassing Heat Exchanger

Have never heard about having a cat/ heat exchanger leak before. We are talking about a Gen3 here, so top of the list for causes of overheating is (early stage) head gasket failure. Here are two tests for a mechanic to perform.

1st test is (on a fully hot engine) to pressure test the cooling system. Here a pump with a gauge on it is attached to the radiator in place of the cap and the system is pressurized to the max allowed (15psi?). Leave the car overnight with the system pressurized. Next day remove the spark plugs and use a videoscope to inspect the cylinders for any coolant.

2nd test is to remove the spark plugs and radiator cap. Next manually turn the engine crankshaft until cylinder 1 piston is EXACTLY at the top of the compression stroke. Use a compression tester hose (with the check valve removed) to pressurize the cylinder with (150psi) "shop" air. If there are any head gasket seeps then coolant and air will push out of the radiator neck. Turn the engine to bring the next cylinder in the firing order to Top Dead Center and repeat the process.

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Gen 3 has no radiator cap /

 

The degas-bottle system used on Gen 3 means that the cap you see on the degas bottle is the only filler cap in the engine cooling system, and it's the one you remove when doing a leakdown test.

 

Jacob, did you ever figure out the overheating issue? Maybe there's some large calcium coolant deposits stuck in the coolant system. Have you tried flushing via the large upper/lower coolant hoses with a garden hose?

 

I saw you mentioned in your post that you once bypassed the heater core on your gen 3 Prius can you tell me how how to pass it i have Gen 3 with a heater core problem, and want to do bypass it if you have picks that would help also

If you have pictures or a video of the heater core problem that would help also thanks

 

:: bump ::

I see people talking about a bypass for the Gen 3 exhaust-coolant heat exchanger, but not the how. I could really use that information, please!

 

i don't recall it ever being done, but maybe i missed it

 

OP started a new thread, on same car, same saga, and forgot a "minor" detail.

What's the miles on it? Original water pump? EGR ever cleaned?

 

Ok, so I decided against waiting and went ahead and did it. To the next person who finds this thread, I apologize that I didn't video record the effort for you, but FWIW, here's some kind of write up for you:

The lower hose is relatively easy to see once you raise the driver side. I started by clamping off the lower hose with some $5 straight nose locking pliers. But what YOU are going to want to do is remember to go ahead and use that second set of those $5 pliers to pinch off the upper house as well, before proceeding.

Believe me when I tell you that upper house is there, but it's tucked up in there, I'm sorry to have to tell you. Make sure - REALLY sure - that everything down there is cooled off before you stick your hand up in there (just like you were sure to chock the wheels and use a jack stand!).

Ok, now that you pinched off both of your hoses - leaving plenty of room to back the hose clamps off - you can pinch that bottom hose clamp with your pliers and slide it back into the hose, past the point where it's covering the pipe.

Now take your channel lock pliers - it if you're fancy enough to have hose pliers - grip the hose where it covers the pipe, and twist it back and forth to break it free from the hose. Then, you can grab it further back with your hand, and wiggle it free.

Now, even if you remembered to pinch off both hoses and did a good job of it, a little coolant is still finna come out at this point, so be prepared.

Next, your gonna wanna have a 3/4" brass 90° barb from the PEX section of the Lowe's where you're doing your shade tree mechanicing in their back parking lot. Go ahead and stick one of the barbs all the way in the lower hose, then pinch that hose clamp spring and slide it back on. Make sure the free end of the 90° bend is pointing up.

Alright, now if you have one of the aforementioned fancy hose pliers, you might could get it up in the little space good enough to wiggle that upper hose free. If you're like me and just working with some channel locks and long nose pliers, well then you're gonna be lucky just to get enough space to get that hose clamp spring backed off. You sure ain't getting that hose broken free of the pipe and wiggled off - save yourself the effort!

So what I did - IDK that I recommend this part, but I include it for the sake of thoroughness - is that I took my tin snips/aviation shears and just cut it off.

Now, be aware that this is going to cause more coolant to drain from the heat exchanger.

Now it's just a matter of placing the other barb end in the upper hose, sliding the corresponding hose clamp to secure, removing the locking pliers, securing the hoses (I zip tied the brass elbow to the upper pipe), and adding coolant back to the reservoir.

If you're reading this, I hope it helps!

 

congrats! thanks for the write up

 

The "why" still puzzles me; were you experiencing coolant loss? On a third gen that's typically due to head gasket failure, not leakage in the Exhaust Heat Recovery system.

 

This is my why... after watching this video and learning how to tell if you have a head gasket leak I decided to diganose mine. Although the Prius in the video is a Gen 4 the Gen 3 does have a heat exchanger and I think mine might have failed. It seems to me that moving 2 radiator hoses as a test is worth the work before spending the time that it takes to replace a head gasket.

I have a 2013 Prius plug-in that I bought with 150k miles. It now has 225 and I am losing coolant. When I did the pressure test to check the head gasket I pressurized it to 17lbs for about an hour. I then checked the cylinders for coolant and did not find any but the exhaust pipe was full of coolant. I want to bypass the heat exchanger temporarily to see if it stops losing coolant as the exhaust pipe is the only place I can find coolant leaking.

 

Thanks for making the effort to document. I already had to remove the windshield wipers to do a compression test and check cylinders with a scope so if you're having trouble working with space you can always do that and likely would not have to cut your hose. I am going to try it as soon as I am able to and see if it solves my problems with coolant leaks.

I saw some videos on 4th gen Prius that allow you to do it without the 90-degree elbow but since I can't find one on the 3rd gen Prius I will probably just use that method.

I think I will also pressure test my heat exchanger while I have it apart to see if it is actually leaking.

 

Once you get finished bypassing the heat exchanger, just do another pressure test. You should want to test your work, before buttoning everything up again - only to find you left a loose clamp. If it passes, you've got your leak, by process of elimination. If it doesn't pass, then check your heat exchanger.

 

I'm not sure I follow. It sounds as if you are talking about the heater core heat exchanger (between the firewall and the dash). Maybe this is my mistake, but I thought this was about the exhaust heat exchanger (under the car).

Well, let's hope that isn't the case!

There was coolant loss, but more to the point, there was a "foaming" of the coolant (causing it to run out the top).

 

Out of the top, of the coolant reservoir?

Sitll would be good to answer these:

 

Miles on it are <1,000 since it was swapped, and unknown "low miles" before.

The water pump may be original since it was low miles? But when Ish swapped the motor, he might have swapped the water pump, since it was just replaced on the old motor in October.

I believe EGR was cleaned in October (when the old motor was in it).

When the bypass didn't solve the issue, Ish found a radiator fan was going bad. He replaced it earlier this week. I'll spare going into details in this thread, as I already have a separate thread started on this, and I originally only popped in to find out how to perform the bypass, and then see if I could help by adding the write-up.

Thank you for your continued concern, Mendel, and please check out the other thread, if so inclined. I just want to avoid jacking someone else's thread, is all.

 

Yeah found:

Gurgle, weak heater. | PriusChat