93 chev 5.7 LOW engine temp

My friend has a 93 Chev conversion van with 5.7... poor heater output. He has an aftermarket temp guage that shows engine runs about 125 degrees F. He also told me the Dealership replaced the thermostat and it didn't seem to
help. I attached my Snap on MT2500 and confirmed that ECM sees about the same temperature as his guage does. We headed down the road (it was about 35 to 40 degrees F that day) and I watched engine temp fall to about 110 F. Then he shows me this receipt from the dealership which I will quote below:
CUSTOMER STATES HE NEEDS A NEW THERMASTAT (yeah, that's how they spelled that) VAN HAS POOR HEAT LAST FEW DAYS. DOES NOT SEE ANY LEAKS ON GROUND AND HAS NOT ADDED ANY COOLANT NOTE: HAS AFTERMARKET TEMP GUAGE, BOTTOM LEFT OF DASH IS ACCURATE VERIFY CONCERN, CHECK FOR LEAKS NONE, ENGINE RUNNING COLD, SUSPECT THERMOSTAT REPLACE THERMOSTAT AND RADIATOR CAP. CAP LOOKS OLD, TOP OFF COOLANT AND BLEED SYSTEM. ROAD TEST. ENGINE STARTED TO COOL OFF ON ROAD TEST, CONSULT WITH 512. RECHECK FOR AIR IN SYSTEM, NONE. SUSPECT THAT THE INTAKE MANIFOLD GASKETS TABS HAVE ROTTED THRU AND LEAKING COOLANT BACK INTO ENGINE. WILL HAVE TO REMOVE INTAKE MANIFOLD CUSTOMER DECLINES, SEE ESTIMATE.
Anyone ever heard of such a thing causing low temp?? ... leaking gasket that isn't dumping coolant outside of engine, nor into crankcase as there is no coolant in oil or white smoke in exhaust?? Can this be just allowing coolant flow that is bypassing the thermostat and keeping engine temp very low??
I'm assuming the dealership really did change the thermostat... "assume" is a dangerous word... but they billed him 288.03 total! Ha! Estimate was $85 (I guess to just see if heat is really poor), then revised to $250.00, then revised again to $299.00 !!!! Below that is another estimate: INTAKE MANIFOLD GASKETS: $495.00 PLUS LUBE OIL AND FILTER: $29.95
at $300 to do the thermostat, I'd guess the intake gasket job would get "revised" a couple times along the way as well??? And experience or thoughts regarding this engine running too cold that can be something other than thermostat bad??? Thanks!
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To check coolant temp vs the guage, I pop the radiator cap off (when cold of course) and place a thermometer in the coolant. Start the engine and warm it up, watch the temp and coolant. The coolant will circulate when the thermo opens, eventually the temp will stabilize, and should be close to 195 or the thermo temp. If your scanner reads the same as the dash gauge then both of the temp sensors are good. Did you drive and Check the temp? The ECM sensor could be bad above 125F.
Also a rich mixture will cause a temp drop, not sure if it would cause your problem. But when the temp is high enough the ECM will richen the mixture to cool things off. Take a look at the Fuel pressure regulator and see if its leaking, this is common with old FP diaphrams.
Cheers
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Yeah thanks, it runs right... block learn...integr... no signs of radical enrichment, stumble, misfire,... definitely just not running up to temp... to tell the truth, I'm wondering if the dealer never even changed the thermostat! I'm a mechanic myself part time (bad back) and I've seen insane quotes for outragous prices for work that did NOT need doing whatsoever... like 600 for rear brakes on a Jeep added on to an estimate for 1200 for exhaust work. I tightened the front nuts which swung the front pipe back into place to stop hitting the front driveshaft, the proceeded to the rear brakes (the job I thought I'd make a decent buck doing) to find it had aftermarket linings in it that weren't even dirty yet... no wear whatsoever! Anyway, that's getting off topic, but this rig just acts to me like it needs a thermostat. Unless there are passages in the intake that are normally quite restricted by the gasket and now are not due to these (tabs rotted), and these passages allow much flow through the bypass (which I thought only really went to the heater core)... Anyone know what "consult with 512" means? I've googled that along with searching out "... cold running... and intake gasket problems..." and find nothing along the lines of an intake gasket making it run cool, making me think the dealership was pumping him big time. If problem is intake gasket, that is fine. And I'd probably refresh the injector fpr unless it was bone dry and looked like it had maybe already been done. I don't think rich mixture would make it run cool to this extent.

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It's not uncommon to get a bad stat right out of the box. It happens often enough that I always check them before installation.
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Martin, when you put a thermometer in the radiator cap hole you are measuring
the coolant temp on the cold side of the radiator. On my 97 Yukon with a new dual core radiator, a calibrated industrial thermometer reads about 150-160 degrees vs. 193-197degrees on the scanguage even with the airflow to the radiator blocked off with a sheet of plastic and the engine running at hi idle (about 1200 RPM). The way the heater/bypass lines are routed I would suggest that the OP have his friend try to back flush the heater core/hoses to see if that doesn't solve his problem before he throws any more money at it. Also have him burp the cooling system to make sure there is no air trapped in there. Remember, this is a van so there is more hose to plug up or trap air. I always try the cheap/free things before I spend any money. As Scotty said in Star Trek, "The more they tech the plumbing, the easier it is to stop up the drain." I'm thinking this could solve both problems.
Regards JR
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He
F.
seem
35
spelled
"assume"
then
cold
stabilize,
and
have
it
OP here : ) Heat was fine and temp guage fine until recently. I don't think problem is plugged heater core, and that certainly wouldn't make engine run cool. Temp guage 125 while scanner reads 120. Drive down road and both drop nearly 10 more degrees. I need to replace his shifter cable later this week (pops off ball on steering column sometimes) so I'll do his thermostat for him while I have it here just to be sure. I still find NOTHING regarding what dealership claims may be the problem!
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On 3/25/2009 10:09 AM, In2hoppn wrote:

What kind of climate/temperature are these being recorded in? Cooling system is pretty simple. If it is running cold like this, unless heater bypass circuit is taking a lot of heat from water (meaning it is very cold out) you have a leak in thermostat area that is letting too much coolant into radiator before engine fully warms up. Try a different Tstat of a different brand too and make sure that there is not bypass leakage in housing around it.
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Check the fan clutch as well. If it is stuck the fan could be working full time and causing it to run cold.
--
Steve W.

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I must disagree with that statement, although I have seen bad clutch fans cause overheating at low speeds and in traffic. Thermostat should keep it hot enough even if fan was a direct mount, as well as when the rad is going down the road at 55, which is more air flow than by the fan alone. But I'll count you in as one more vote against the intake gasket foolishness stated by the dealership mechanic! And I can tell by the sound that the fan clutch is working.
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Thanks to you and all responses. I'd have to say the consensus here is what my own thinking is... This intake gasket thing is total BS! Either the thermostat was a bad one off the shelf, or it never go changed. And either the mechanic involved is a total idiot, or making it up as he goes to try to rake some more bucks out of this poor fellow. My personal thought is the latter of both those two statements! I'll follow up when it comes back for me to work on! In2
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