Overheating problem

[BAMA-Z-RER]

Ok so my z is overheating. I've done new radiator, water pump, fans are fine, t-stat, and hoses are fine. I get bubbles in the radiator. I have had it checked for head gasket leak and it comes up negative. Also had coolant system pressure checked and it checked out fine. I get no heat in the cabin. I'm getting impatient with this problem. When I had radiator replaced a month ago it ran fine for a few weeks and then started doing the same thing again. Can the heater core go bad and put a constant stream of bubble into the coolant? Where else can bubbles come from in the coolant? I'm lost and so are my mechanics. Please help.....

[GerryO]

How was it tested for a head gasket leak? How does the underside of the oil cap look? Post a photo. How badly has the engine been overheated in the past? How much rust was in the coolant system, has the coolant been changed regularly and its' concentration properly maintained in the past, and was the coolant system flushed completely before the new radiator was installed?

Have the coolant tested for oil. It's supposed to be a very conclusive test for a BHG.

Sounds like a BHG and one of the heads could be warped or eaten by corrosion, that the heater core could be clogged with rust and that the new radiator could also now be clogged.

All this is based on an nice MR2 that my son purchased, that only had a bad/leaking water pump. The owner kept adding water to maintain the coolant level, depleting the concentration of the corrosion inhibitors and also making it less effective at preventing overheating. Eventually the aluminum head was eaten by corrosion/electrolysis, the heater core and radiator were clogged with rust, the head gasket was blown and there was oil in the coolant. A compression test wasn't useful in detecting the BHG.

A bit of welding and resurfacing repaired the head, a lot of flushing got rid of the rust, but pulling the heater core was a bear.

Join the MR2OC to read this:

http://www.mr2oc.com/showthread.php?t=224420

[Towncivilian]

If you haven't yet, inspect the radiator cap following the instructions in this TSB and replace with a new OEM one if necessary.

[aroche25]

Can the heater core go bad and put a constant stream of bubble into the coolant? Where else can bubbles come from in the coolant? I'm lost and so are my mechanics. Please help.....

When the heater core goes bad it can start to leak coolant which in effect it will be replaced with air, which can cause bubbles. Mine just went bad so I had to bypass it, till i get around to pulling the dash out and replacing it.

[nissanfreak12]

How do you know that the T-stat is fine? Visually wont tell you anything, plus what everyone said.

[buloushie]

How do you know that the T-stat is fine? Visually wont tell you anything, plus what everyone said.

I have always put fail safe t stats in mine,IE when they go bad the fail open not closed,plus to test one put it in a pot of water bring to temp of t stat and see if it opens.but my guess bad heater core.

[nissanfreak12]

How do you know that the T-stat is fine? Visually wont tell you anything, plus what everyone said.

I have always put fail safe t stats in mine,IE when they go bad the fail open not closed,plus to test one put it in a pot of water bring to temp of t stat and see if it opens.but my guess bad heater core.

My experience fail safe SUCK! Spend the money and get an OEM or the stant premium. I am also with you on the heater core or cap.

I am just wondering if the OP tested his thermo the way you said it.

[BAMA-Z-RER]

The mechanic is now telling me the T-stat is not opening. So I know that has to be replaced. But where are the bubbles coming from. I get a constant stream of bubbles. It gets worse when I rev the engine. The bubbles become almost frothy. My mechanic is suggesting a 120,000 mile service which would run 1200. My thoughts are that the head gasket could be blown. I don't want to do one and then have to go back and do the other. If the t-stat isn't opening then would the waterpump pull bubbles in through the seal?

[mrmoose]

Head gaskets... If the tstat was not working they would have over heated and warped in no time. If I were you I would find a mechanic that knows z's, or a more knowledgeable one...

[BAMA-Z-RER]

What are some good tests to be sure of the head gasket? He says he has done a gases test and it's negative, and a leak down test. The result of the leak test was -2 lbs in 2 hours. He said that was normal.

[mrmoose]

Well at least have him do it again, if the core is bad it could have leaked out coolant and caused overheating and warpage. Are you loosing coolant? Try bypassing the heater core with a 90 elbow if I you are loosing any. But the bubbles in the rad are def a sign on bad head gaskets, just went throught this myself when a turbo coolant line blew and my heads warped...

[GerryO]

http://www.youtube.com/watch?v=ON_RtokUohI