wjogert

Replaced cam, lifters, timing chain. WP changed 3 years ago, but sat since (due to the engine issues). Changed PCM coolant sensor (dead).

Engine together, runs nice. Have a small coolant leak from WP weep hole and also from the stupid Duralast sensor threads. Even taped the threads, but still drips.

Anyway, start car and let idle... gauge goes to normal "fan on" point and fans kick in, temps drop to about 3/4 gauge. Seems normal.

Did notice that the radiator hose going to thermostat tends to "inflate". Increases in diameter about 1/2". If I squeeze it, it's rock hard with pressure. Original hose, so thought maybe the rubber is just soft.

Now driving... temp gauge remains around the 1/2 mark UNTIL I stop at a light. Within seconds the gauge shoots to the "fan on" point. Start to pull from the intersection and the engine bucks and hesitates like serious pre-detonation. Get car moving, temps drop some but not below the 3/4 area of gauge.

Parked the car and listened to the sounds of a very hot engine starting to cool (metal expansion sounds).

Changed radiator cap and thermostat. No affect.

Gauge has never "overheated". Exhaust is clear. Oil is clean.

I did have to replace the heater hose/pipe (one with bleed screw) with straight hose. The original got nicked during the engine work. Could this behavior be just a trapped air pocket??

I've considered that the bucking could be coolant on the optispark, but will address that after the cooling seems resolved.

timnfxr

Have you bled the air from the cooling system? If the water pump weep hole is leaking, it will shorten the life of the opti.

Injuneer

Taping the coolant sensor threads, plus the sensor threads not being tight enough to seal correctly, could raise the resistance of the circuit. Higher resistance would lower the temperature reported to the PCM, causing the fans to come on too late.

wjogert

I thought the 2-wire sensor for PCM didn't use a ground connection through the housing?

Injuneer

Good point, would make it a remote possibility with the 2-wire. Additionally, the coolant dripping on the sensor could alter the readings. You need to check the readings being sent to the PCM with a scanner, to see how they compare to the dash gauge.

The fans should start on low at 226*F, and switch to high at 235*F. The 3/4 mark should nominally be the 235* point +/-. Are you using the LT1-specific t'stat?

You mentioned you no longer have the bleeder on the heater hose. Did you use the one on the t'stat housing?

ACE1252

Get some Permatex high temperature thread sealant for the sensor. Drain the coolant level before changing it or you may wash the sealant off the threads(if coolant is rushing out the hole).

If you are running at the 1/2 mark(should be around or just over the 1/4 mark) when cruising then it does sound like it's running hot. If you are in city traffic, it will run hotter with the stop and go...but the fans should bring the temp down easily.

To Injuneer's point, did you open the bleeder on the thermostat housing when filling the system with coolant? Did you follow the proper steps to fill the LT1 cooling system? There is a specific way to deal with the reverse flow cooling system....

With the water pump weep hole leaking, you need to go ahead and get the water pump replaced....the writing is on the wall when that hole starts to leak.

wjogert

I filled the system the same way I've always done after WP replacement (this is probably the 4th pump for this car)... but can't say I followed any LT1 specific process. I opened the heater pipe bleed screw, filled radiator until coolant exited the bleeder, closed the bleeder. Started engine with radiator cap off, continued to fill radiator until it was full and put on cap. Run engine until fans cycle, top off coolant reservoir.

I've never used the thermostat bleeder and never had an issue before. I opened that bleeder yesterday with car off and instant flow of coolant (no spit or hiss), so fairly confident that it's ok there.

Drove around with scanner on. Started driving cold, temps rose to 160 and remained there for 5-10 minutes of driving. Stopped at stop sign and temp increased and remained about 180-190. Stopped for a light. Temp shot to 230's. Even though continuous driving after that, temps remained over 200's. Parked car and let idle. Fans turned on at 238, and shut off at 233. That cycle repeated for 10 minutes of idling. Took car on highway for about 2 miles (65 mph), temps dropped to 190, until I exited and then back to 200's.

So according to PCM, there is no overheat... but I feel like the temps should be lower. ?

BTW, I saw this on another forum and I wonder about the crossover pipe. The car has sat for 6 years, drove lightly for one summer (that's when I replaced WP last, lol), and sat for another 3 years. (F'ing WP has less than 200 miles on it, grrr.)
My heater core gets hot, so not worried about that or the flow restrictor. But I've heard of coolant boiling in the heads if the crossover pipe is clogged or eliminated. ?

wjogert

I was considering using plumbing paste, but the high-temp sealant is a great suggestion

Yes, I fully intend to replace the WP (again)... but summer is almost over, and with my limited free time all I've done is work on this car... no joy of just cruising. I was hoping to finish off this season and switch to an electric WP conversion next season, lol. But it's getting worse. The 1 inch stain overnight is now a 5 inch stain overnight. Grrr. Whenever I do change the pump, I'll install yet another sensor too.

Found this pump on Amazon:
https://www.amazon.com/Speedmaster-P..._cd_al_qh_dp_t
High Volume pump for 93-94 LT1. I think all 93-97 LT1 use the same pump though??

Injuneer

Does the steam pipe from the rear of the heads get hot? That will tell you if it's flowing. I've had Dex-Cool in the car for almost 20 years (replaced per manufacturer's recommended interval) and never had a problem with clogging of any sort. I actually have a second coolant temp sensor in the steam line from the back of the heads, and its basically the same temp as the dash gauge.

Eliminating that line can cause #7 and #8 to run excessively hot, leading to detonation (which causes knock retard). It's venting any air in the back of the heads and steam that can form. There's a vapor/water separator in the radiator, where the line eventually connects (after it goes through the base of your throttle body).

But before you had the bleeder on the heater hose (although the two quotes appear to contradict each other) . Useful to open the t'stat bleeder as you fill the radiator, lacking the heater hose bleeder.

Have you checked to see that the fans are actually running when they are supposed to? Have you checked for obstructions in front of the radiator? What are the local air temperatures where you live? Is the coolant clean, 50/50 mix?

wjogert

So, when I first filled the system, the original heater hose was in place, but it had a leak. I tried to repair it, but finally gave up and installed the straight hose. Merely topped off the coolant that was lost from hose swap.

Fan are definitely running. No obstructions. Local temp was ~80F. Fresh coolant, probably a bit stronger than 50/50 (we get well below freezing here, so I mixed it a bit strong). I'm going to get a coolant tester to see just how strong, perhaps I need more water.

Can anyone comment on that pump compatibility? EDIT: NM, looked it up at rockauto and all the listings say 93-97.

Injuneer

As long as its for an F-Body LT1 you are fine. B-Body and Y-Body LT1 pumps are slightly different.

From Shoebox

http://shbox.com/1/lt1_water_pumps.jpg