View original topic: High CHTs Page: 1, 2  Next
samwise Wed Jul 11, 2018 8:39 am

Bus: 1979 California-spec, 2-liter engine, FI (not running Hall effect distributor, but 205P instead).

Symptoms: 96f air temp, 4th gear, 50mph on the flat. I'm seeing CHT temps (according to DD gauge with sender under #3 spark plug) of up to 425, with climbs to low 430s for slight inclines. This is with the oxygen sensor disconnected - with it connected, same stretch of road, the CHT peaked at 448 on the incline....

I know I have some missing stuff for the factory set up - thermostat and associated parts are missing, no tin under driver's side pushrods, no exhaust heat shield (I think - I'd have to get under to check that again), no dump tubes. Catalytic converter is non-original as a PO welded one one, rather than one attached to the proper bolt holes.

I'm guessing that I need all of the above to help reduce head temps, so where's the best place to get 1979 California-spec stuff now that Bus-Boys has closed down?

Wildthings Wed Jul 11, 2018 9:55 am

Sure you are getting a good seal on the #3 spark plug? When the ring gets messed up and gases begin to work their way up passed the threads the thermocouple will read very high.

malcolm2 Wed Jul 11, 2018 11:11 am

I know..... you are talking about a bus, but those temps would scare me too. Get your fan and cooling tins set up, maybe move the sensor around and see the other cylinder's temps.

Good Luck

airkooledchris Wed Jul 11, 2018 11:52 am

Did you just install the gauge recently, or has there been a change in your numbers?

Did the PO weld a CAT in the stock location, where it's RIGHT next to the stupid #3 valve cover like it was originally on the 79CA setup?

Be sure to read the other thread you have going right now, there's some really useful data there.

samwise Thu Jul 12, 2018 7:25 am

Gauge has been in for a couple of years, but I don't remember the old readings as the bus has been down for about a year with a starting issue that life got in the way of sorting.

Cat is in the stock position for a '79.

Engine appears to be running fine otherwise. Emissions in April this year:

Seems to run very lean with the oxygen sensor wire attached (Carbon Monoxide of well under 1%) - too lean, causing the current head temps?

jtauxe Thu Jul 12, 2018 7:42 am

It seems that people are hinting that this could be a temperature gauge issue, and perhaps not an engine issue. Is your engine actually that hot? Does the shroud feel hot to the touch? Do you feel excessive heat radiating off it?

airkooledchris Thu Jul 12, 2018 9:43 am

certainly do NOT run with the O2 sensor connected. you don't want it to be THAT lean.

425* at only 50MPH flat ground is just WAY too off to think about this as a simple tuning issue.

make damn sure that #3 plug is well seated against the sender. If there's any gas escaping near the plug it'll throw your readings false high by a LOT.

seriously, while the missing tin and heat shield might help a little, it's nothing bad enough to give you 425* at only 50MPH flat ground driving.

You have homework:

1. double check how well seated that plug/sender is.

2. check your timing. pull and plug the vacuum from the distributor and see what your timing is advancing to when you are at Wide Open Throttle. What is this number?

Bendejo Thu Jul 12, 2018 4:09 pm

5th at 40 is too slow. Try a downshift and report back.

my59 Thu Jul 12, 2018 4:51 pm

I've a 79 with oval heads and exhaust with a cat, Fed. model, and at 50 in 4th its an unhappy lugging 2.0. There are a couple of speeds between 2 and 3, and 3 and 4, that the bus just hates.
Temps you are seeing are very high for gear/sped combo. Sure its level ground? Flat/level are not the same. Headwind? Plenty of oil? Get the tins in, make sure the flaps are open, your engine not covered with pounds of oily dirt, lower tins in, engine seal solid....

FullFender Thu Jul 12, 2018 6:08 pm

Have you tried So-Cal imports located in longbeach?

Tcash Thu Jul 12, 2018 11:12 pm

Here is some apples and oranges to compare to.

Tcash Thu Jul 12, 2018 11:17 pm

You know the drill
Tune up
Finding vacuum leaks with smoke (smoke test, tester)
Fuel Injection Fuel Pressure Testing
Testing FI Fuel Pressure FAQ
Looking for plugged injectors.
Fuel Injection Leak Down Test

Good luck

Randy in Maine Fri Jul 13, 2018 6:49 am

That is about as hot of a set up from the factory that you could possible get.

I have a couple of 79CA complete exhausts in my shop just sitting around but I am not coming out the SLC this year.

Suggestion...after you do a smoke test for vacuum leakage, and a fresh tune up, you may want to investigate cleaning and calibrating the injectors for about $100. It would be nice to get a LM2 on there to see what kind of air to fuel ration you are really seeing.

samwise Fri Jul 13, 2018 7:34 am

Having been looking around the bus, it appears that someone fitted a 002 transmission at some point in the past - could that affect it, too?

Injectors were brand new in 2012 when the engine was rebuilt - they could, of course, be blocked, although you would hope not.

I'll check fan shroud heat when I get home tonight - it'll be about 95f when I drive home, so we'll see how that factors in.

I will check the plugs, and try to get #3 to seat back properly afterwards. Timing scale is on its way to me for checking the timing, although I do have some marks that Colin put on the shroud itself.

Using virtually no oil at the moment, which is nice, although I do have some minor drips from either valve covers or pushrod tube seals. In general, the engine appears to be running really nicely: smooth, no audible sounds that I'm worried about, pulls well, checked oil yesterday after getting to work and dipstick wasn't too hot to handle or anything.

Place where I saw the mentioned temperatures was a 25ft incline over just under a mile, so nearly flat. The CHTs do go up and down nicely - I can see a 20+ degree drop when waiting at lights for 90-120 seconds, and this morning, driving at 50 in 4th on a fairly level section, I was seeing temps around 350-360 (76f air temp).

Randy in Maine Fri Jul 13, 2018 8:17 am

CHTs are directly related to how HARD you are pushing on the accelerator pedal. Work = heat.

I like to have a little pedal left even going up a hill and I like to downshift a bit earlier as opposed to later.

The 002 is geared down a little compared to a 091, which should actually be a bit easier on the CHTs. I assume you are running fairly correct tires and properly inflated.

SGKent Fri Jul 13, 2018 9:38 am

My opinion: you are a just tad lean. Just a tad. Maybe let two notches off the spring wheel in the AFM, be careful to mark it where it was because if it slips it will unwind like a clock. The proper way is to move the slider but without an air to fuel meter it will be hard to do. Also make sure your timing doesn't exceed 30 BTDC with hoses off and at full RPM where it stops moving. See if that doesn't help lower the CHT 25 F to 30 F without affecting performance or MPG.

samwise Fri Jul 13, 2018 3:34 pm

Could hold my hand on the fan shroud for 4-5 seconds before it got uncomfortably hot.

raygreenwood Fri Jul 13, 2018 4:21 pm

Before you start tweaking anthing.....check fuel pressure...because that can run you lean and check carefully to make sure you have "0" vacuum leaks....which csn also run you lean. Ray

pittwagen Fri Jul 13, 2018 9:00 pm

I also have a 79 CA spec bus. My 50mph CHT temps are around 375 @ 70 deg or so. 60mph is 400 on the flat. Hard to tell exactly with the VDO. My sending unit is attached to the head near the spark plug.

Looking back on the smog tests from 2010-2014 my numbers are somewhat higher than yours. My cat is there but completely hollowed out on the inside. I never had a problem with the smog tests including the NOX test. Smog tests ended here in 2015 so I have no current numbers to compare.

My engine is about 7 yrs old and I do want to swap out the CA exhaust components once I find all the pieces. I do run a turbo exhaust.

I did disconnect the O2 sensor for a few days. Had to adjust the idle as it dropped down close to 200 rpm. Engine did run somewhat cooler and had a bit more power higher up the rev range but seemed to load up at idle when hot. In hindsight I wonder how sophisticated the CA ECU is and if I should have disconnected the battery to cause the ECU to reset itself, if it has that capability.

I may buy the Innovate MTX-L Plus to see what the AF readings are especially when the O2 sensor is connected/disconnected with the current setup. I need to find a place to weld in a bung downstream of the existing O2 sensor location. Then I will be able to compare to the non CA system once I install that.

I will also check the fuel pressure. I think my regulator may be the original as the bus only has about 120,000 miles on it.

SlowLane Sat Jul 14, 2018 4:06 pm

pittwagen wrote: Smog tests ended here in 2015
Wait, what? AirCare is no more? Damn!

Quote: I wonder how sophisticated the CA ECU is and if I should have disconnected the battery to cause the ECU to reset itself, if it has that capability.
Based on the AFR readings I get on mine, not likely. The ECUs from that era are purely analog devices. There's no internal cache of sensor history that would be cleared by a reset.

Quote: I may buy the Innovate MTX-L Plus to see what the AF readings are especially when the O2 sensor is connected/disconnected with the current setup. I need to find a place to weld in a bung downstream of the existing O2 sensor location. Then I will be able to compare to the non CA system once I install that.
Don't know about the MTX-L, but I have an Innovate LC-2. It provides two channels of output from the wide-band O2 sensor: one for the gauge, and a second that can be programmed to act like a narrow-band sensor. If you use one of these (or whatever Innovate has replaced it with) you can replace your existing sensor with the wide-band sensor and use the second channel to drive the ECU O2 input directly. No need for another bung. I did exactly this when I first converted my system to CA-spec.

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