Red Hot Mama! (1 Viewer)

[Roobah]

Red Hot exhaust manifold

Hey All,

Been searching and gathering alot of great info on here while I work thru this issue on my FJ80. But I've run into a dead end on my searches and here goes my request for info/help..

Noticed my 80 was bubbling coolant back into the overflow tank, it was a pretty loud bubbling/gurgling too. This was after driving slowly up a 1mile dirt road with AC on after a 60mile highway drive with AC off. I had heard this noise before but just thought is was normal transfer of fluid back to the overflow tank. But this time is was too loud to be normal. Temp gauge never budged off it's normal spot but I've learn here that these gauges are not "real" gauges but more like on/off gauges.

Did the bubble test and no bubbles can be see. So for now I think the HG is ok. For now.

Changed radiator cap. On my test drive I stopped at the top of a hill to listen for gurgling and it was still there. In hindsight wasn't a good test because I was driving up a steep highway hill at 50+mph. But when I raised the hood to listen for the gurgling I saw my exhaust manifiold was glowing orange ( it was dark so easy to see)...OK title should have been Orange Hot Mama but that's not as attention getting! Got home 20 minutes later after driving on flat roads and manifold wasn't glowing anymore. So, two problems maybe or maybe they are related?

Next put in a blue fan clutch from CDan. Old clutch didn't have the start up roar the new one does ,so old fan clutch was definitely NG.

So, next test drive. Gurgling is gone...but exhaust manifold was still glowing hot...this was again after climbing a highway hill (hwy 17 in Santa Cruz mtns) with AC on .

Research here inidcates a clogged exhaust might be the culprit.

Pulled the second cat converter today and it looks good, not clogged. And the exit of the first cat looks good.

BTW you can get the second cat on/ off with the Hanna sliders in place!

So, on flat roads the mainfold doesn't appear to glow but when climbing hills at 50mph at 2600rpm with occasional stomps up to 3400rpm the manifolds get orange hot. Here's a clue maybe..the 80 didn't want to maintain my stomps at 3400rpm for long, it would do it for couple seconds then shift up again and drop rpm.

Anyways orange hot exhaust manifolds what causes them? O2 sensors? Running lean? Checked the timing tonight it was 2.5deg.

The truck is actually running great if I hadn't heard that gurgling noise the other day I'd be oblivous to my red/orange hot mama-manifolds.

 

[-Spike-]

Runnig rich would be my (very uneducated) wild guess. Or completely normal for driving her hard.

-Spike

 

[F0RSAKEN]

Lean, not rich, and a clogged cat could be the cause as well.

 

[Roobah]

So, vac leak and then maybe change the O2 sensors (which are original with 144k) is next on my list. Both could cause a lean mixture condition. probably several other things can too...like what? Have a short trip planned to the mtns in a couple weeks and want to get this fixed before then.

So nobody has seen this issue before? Around town the manifolds are not hot but climbing a hill on the freeway at 2600 to 3200rpm for a several minutes got them orangy hot.

 

[TLCnoob]

I'd check that front cat more closely. Clogged cat is my guess. Any tune up stuff lately, missing, etc.? Spark plugs of the wrong heat range?

In my case, installed wrong plugs in an LT1 and it developed a slight miss. Over time and lots of raw fuel dumped into the cat, she stopped up. After I lost a light to light race with a Mustang, I knew something was wrong. Headers were orange after driving for 10 minutes or so, and a new cat fixed it right up.

 

[Roobah]

I can only see the outlet end of the front cat and it looks fine. There's no joint at the inlet end of the front cat to seperate. The exhaust tube from the exhaust manifold is welded to the inlet of the front cat. So, how do you check that end of the cat?

Nothing changed on the engine recently and it runs great except for maybe some power loss climbing. But that's even hard to say because it might have been a gradual loss or no loss at all and I'm just looking for things.

 

[TLCnoob]

I guess it would take a trained eye to tell if the cat's dead, I'd probably just let a mechanic cut it off and have a look. May want to talk about a replacement with him beforehand.

The exhaust manifold should NEVER glow on a street ride...that's only for Formula 1 headers, etc.

If it is a stopped up cat, you'll probably notice quite an improvement in power with a new one installed.

 

[therealratfink]

Not a trained eye, a temp gun, Check the temp pre and post cat. If it is hotter before it's clogged.

 

[Roobah]

Good idea about the temp gun! Heard that bit of advise from a muffler shop I called today also.
Stay tuned, got to see if I can borrow a temp gun from work.

 

[therealratfink]

If not, allot of mom and pop shops will check it for free.

 

[Roobah]

Well, took the 80 into a family acquaintance’s shop today to help diagnosis this red hot manifold issue….they did a road test but don’t think they went up the steep highway I did when I saw the glowing manifold . So, of course they couldn’t duplicate the issue but here’s the findings…

Exhaust pressure test: drilled a hole in exhaust before 1st cat and installed pressure gauge, saw 4psi at 3800rpm They believe this was good for 2 cat exhaust and indicates the cats are not clogged. I’m sure the 2nd cat is good based on my visual inspection but can’t see inlet to 1st cat so wasn’t sure on it.

Emission test: They said were good.

Idle: CO % 0.00, HC PPM 7, CO2% 14.6, O2% 0.1

2500rpm: CO % 0.08, HC PPM 9, CO2% 14.8, O2% 0.0

Fuel pressure 35psi > good

Air flow meter and oxygen sensor readings both normal and switching…They did a test drive with a PC hooked up and monitoring the 80’s computer..

Highest manifold temp they measured was 600F.

So, they couldn’t duplicate the problem. I’m thinking of asking if I can borrow they’re computer after they close and go up the steep section of the highway which I’m certain will get the manifold glowing.

Also, I’m gonna take a pic of the glowing manifold just to be able to show them.

I’m thinking it has to be a fuel mixture related issue because if it was a clogged cat you would think it would be something which would be more consistent. By consistent I mean if it’s clogged it would be clogged on flat roads as well as steep roads and they should have seen it at the 3800rpm test (which is higher than I ever drive at).

Anyways the 80 isn’t my daily driver so this is just a “fun” little problem to solve... for now. Have a trip in a couple weeks though so want to get it sorted out before then!

So here's some interesting info off the internet..I'm thinking I'm at 885F range

How to tell what temperature a glowing object (metals) might be:

Doesn’t really matter what the emitter is…stainless steel, cast iron, tungsten in your light bulb, the temps are about the same for a given color. Generally accepted colors/temps are:

C F Color

400 752 Red heat, visible in the dark
474 885 Red heat, visible in the twilight
525 975 Red heat, visible in the daylight
581 1077 Red heat, visible in the sunlight
700 1292 Dark red
800 1472 Dull cherry-red
900 1652 Cherry-red
1000 1832 Bright cherry-red
1100 2012 Orange-red

C= Centigrade
F= Farenheit