TPITuned Port Injection discussion and questions. LB9 and L98 tech, porting, tuning, and bolt-on aftermarket products.
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Hey, i was reading that a couple of people were saying that there guages read 220 or so when they connected their whatever tester up is gave a reading of 195 or so. where can i get one of those readers,? And is there a chance that when my car runs at 220 at idle that its actualy lower?
Nope, 220 is 220 and the 1/4 mark on the gauge (1/2 way between 100 and 220) is 175 degrees. I went through the work receipts on my car. The previous owner had a 180 stat installed in 1993, recommended BY Pepboys.
Also found out I have a remanned tranny and a new fuel pump @ 53,000 miles. No wonder this tranny shifts so good!
i thought the 1/4 mark was 160, since 160 is half way between 100 and 220. but then again on the other side its only only a diffrence of 40 from 220 to 260.
There's really not much difference at all between the upper and lower dash marks and the 200. Mine hits 175-185 at around the first mark, then 220 is more or less 220 but just a hair below is like 205 or 195! and quite a bit higher is only 235 since it's not a 1:1 ratio of temperature to distance the needle moves.
The temperature gauge on these cars are far from accurate. I compare my temperature guage to my CTS readings from a scan tool and the temperature gauge is way off. It is NOT to be relied upon.
On my car, the guage tends to read much lower than it really does. The first major hash mark would make you think it is 160*, but in fact, on my car it is around 180*. So below 220*, the gauge tends to "under estimate" the real temperatrue. At 220*, it does appear to be more accurate, and over 220*, the temperature gauge "over estimates".
First, as you noticed, this gauge is not linear. Two hashes can mean the difference of 50*, but the next two may only represent 20*, so its just to be used as a quick reference, thats it.
Second, the sensor for the gauge, and the sensor for the ECM are two different sensors. The ECM sensor uses a ground internal to the ECM, and therefore is more accurate. The gauge sensor is merely a one wire sensor grounding out to the block.
If you have to go by any temp, use the temperature provided to the ECM.
mine never goes past 1/4 and the actual temp is around 170-172 at idle
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87 trans am,gm crate 350(4 bolt mains 10to1),L98 aluminum heads,LT4 hot cam,slp runners,slp 1 5/8 headers,3in.y-pipe,edelbrock base,hi flo cat,air foil,afpr,as&m ported plenum,gutted airbox,t-5 tranny w/centerforce clutch and a 3.27 9bolt(11.9in. brakes),ed wright's fastchip,relocated iat sensor,160 fan switch,tb bypass,accel supercoil,cap& rotor,hollowed maf,slp 3in. catbcak.
FOR SALE!FOR SALE!FOR SALE!FOR SALE!FOR SALE!
EVRYTHING IS FOR SALE WITH MY CAR (EXTRA ENGINE,TPI INTAKES,RUNNNERS,PLENUMS,ECM W/CHIP,ETC.
GETTING OUT OF THE 3RD GEN MARKET BEST OFFERS
CONSIDERED!!!!!!!!!!!
<font face="Verdana, Arial" size="2">Originally posted by FlashGTA: When my gauge reads 220 actual temp is 202 by scantool.</font>
Depends, too, on where the reading is being taken.
On my 86 Vette, the dash guage will almost always be 12 to 15 degrees higher than the temp shown by Diacom.
The dash guage is taking it's reading from the passenger side cylinder head while Diacom is reporting the one being accessed by the ECM which is from the sensor at the front of the manifold.
Naturally, the coolant is hotter in the cylinder head than at the front of the intake manifold near the thermostat housing.
Why would coolant be hotter in the head than @ the water outlet? Considering it gets to the water outlet after it's been in the heads. If it really lost any real temperature just by moving through the hot engine, why would we need radiators?
Don't beat up on me because I said something you'd never come across before.
If you ever saw a map of the different temps of a SB Chevy you'd know that the temps vary around the engine, front to back, top to bottom. Don't take my word for it, ask anyone that really KNOWS the SB Chevy.
Two particularly hot spots are between cylinders 3 and 5 and 2 and 4. This is because of the two exhaust valves being directly adjacent to each other for those cylinders.
#7 tends to run leaner and, thus, hotter too. Because of the firing order, #5 tends to rob #7 of a slight amount of mixture, leaning 7.
Early carburated Big Blocks came stagger-jetted to help cure this imbalance problem and better equalize the A/F ratio to #7 and, in the process lower coolant temps there.
Endurance SB circle track racers regularly modify the cooling system to provide additional coolant to the two areas (between 3 & 5 and 2 & 4)which results in a couple of hundred degrees lower temps there. Holes are drilled and tapped into the head between the offending cylinders and coolant lines are run from the modified water pump to the fittings. You can buy the water pumps already tapped for these hoses.
All ya gotta do is think about it and you'll realize that coolant near the combustion process is gonna be hotter than about anywhere else in the engine.
I wasn't beating up on you, i was asking a legitimate question. Good questions lead to good debate and good knowledge.
Now back to your example. Yes, i am aware that their are hot spots in the head by the center exhaust ports, as well as in the back of an early style intake that doesn't have a water crossover in the rear, etc. The dillemma i can't get rid of in my head is how the coolant can be that much hotter just because it is in a hot spot, when in probbaly a fraction of a second that same coolant is now moving past the CTS/crossover. To a degree it isn't fair to say that it is the 'same' coolant passing the CTS as the potentially hottest coolant from around the center exhaust ports will also be mixing with the cooler coolant from the fringes of the block. And now that i step back and realize that you are only talking about an observed 15' temp difference guage/diacom (i'm assuming your vette has a digital dash {and no i have no idea if it was available in 86 vettes}) that that doesn't seem like an entirely unreasonable difference if the guage sensor is in a relatively dead headed, poor coolant flowing location like the plugs are in.
Unfortuneatly i am beat and i forget the point i was trying to make when i started this, lol.
Some other tid bits I've come across over the years about differing temps:
Remove the stock exhaust manifolds and install a set of long tube headers. The 02 sensor is now installed about, what, 18" or so farther downstream. On a fully warmed up engine the added distance will allow the 02 sensor to cool off below the 600 degree F thresh-hold and the engine, many times, will drop out of closed loop at idle. Now crack the throttle a tad and the additional exhaust flow will allow the temp to again rise and the engine will go back into closed loop. That's one of the reasons heated 02 sensors are so often needed when long tubes are installed.
Rick Hendrix' engine crew discovered that - if I remember correctly - the #1 cylinder runs too cool, so a restrictor is threaded into the block to lessen the amount of coolant that reaches that hole. On the opposite end of the spectrum, Fel Pro recommends enlarging the upper center hole in the block between 2 & 4 and 3& 5 to get more coolant in there. Some blocks come from the factory with the enlarged holes, but some of the older ones don't. I had to drill out my 400 block when I was building the 415 that's in my car now.
I was looking into oil coolers a few months back and found that tests have shown that oil temp at the bearing is 65 to 80 degrees hotter than in the pan. So if you're running 220 at the pan, your bearings can be seeing close to 300 if not more.
The big boys have found that spraying oil directly onto the valve springs allows them to turn 9000+ rpm at the top of the straight-aways and keep the valvetrain alive. Without this additional oil cooling, they can't reliably turn those magical R's.
Steve bought a set of those valve covers from CompCams for the 434 I'm building for him. There are four tubes inside the valve cover - about 5/16" and each tube has two tiny holes from which the oil is sprayed. Fittings are run from screw-in adapter bungs welded to the valve covers using steel-braided line. I plan to pick up the oil at the "T" junction at the rear of the manifold where the oil pressure sending unit is located. I just hope they don't kill pressure at idle.
I'm sure that if I took the temp of the oil just as it exited the pushrod and compared it to the temp of the oil as is enters the holes in the head draining back to the pan, there'd be a dramatic difference too. Valve springs build a lot of heat as you work the engine.
Interesting too is that relocating the MAT from the underside, rear of the plenum to the air filter housing fools the ECM into richening the mixture a tad. I don't have any personal knowledge as to whether this translates into add'l power, but those relocation kits are available from at least a few sources. What I don't understand is when the ECM gets 02 feedback and sees the mixture is too rich, doesn't it just reduce the injector 'on' time only to have to do it all over again?
Has anyone seen 'back to backs' to verify whether this trick works or not?
BTW, yes the Vette has digital gauges. I only mentioned my type of car because there are so many cars running the L98 type engine and temps from other cars may be different depending on where GM mounted the sensors.
I saw an article of an interview with a GM Tech who was involved in the design of the reverse cooling experiment on some later year 350s (forgot which ones). He said the plan was to better equalize the cooling around the engine, but it plain didn't work up to expectations. 'Priority Main' does though and has gone a long way to stopping the 350 from eating main bearings.
