I replaced the heads on my '80 L48 with DART IE heads and installed Jet-Hot coated Hedman headers. I installed the Fel-Pro head gaskets 'dry' as instructed and torqued my head bolts in three increments up to the final 65 ft lbs.

The entire cooling system (radiator, radiator/heater hoses, water pump) are 2-3 years old and I've kept the coolant replaced. The thermostat is about 1.5 years old (replaced it when I installed the Performer intake back in early 2001).

I replaced the 882 heads (engine came originally with 624 heads) that I had installed with the engine overhaul back in 1997 with the new DARTs. The DART's don't have the exhaust gas crossover vent in them so the EGR is inoperative; regardless, I have installed the EGR and plugged the hose that leads from it as a precaution for vacuum leaks.

I also set the lifter preload myself. Could there be sufficient friction from inadequate/incorrect lifter preload to increase oil temps and impact coolant temps? The engine sounds fine; plenty of power and no valve train noises (except that it has erratic idle and dies and appears to overheat to the tune of 240-260 degrees according to the temp gauge).

What about other 'new' sources for heat/friction? The heads have guideplates for the new Summit hardened push rods and new Summit rockers and anti-gall pivot *****/locking nuts. The heads have 72cc combustion chambers (882's had 76cc chambers). I'd say the new heads are as 'port-matched' as you can get to the intake manifold. I cleaned all block and intake manifold surfaces in prep for the new heads (the heads were sparkling clean). I even took the precaution of blasting the heads (combustion chambers, valve areas, etc.) with compressed air to remove foreign matter that may have made its way inside during shipping/handling. The heads have larger valves (2.02/1.60) vs. the slightly larger than stock rebuild valves that were in the 882 heads.

The engine isn't exhibiting horrible performance but it does have a very erratic idle and appears to overheat (which could be causing the engine to die). I mean it appears to overheat since I also had to move the temp sender from the left front cylinder head area to the upper left front intake manifold position. Moved to intake since the heads are tapped for 3/8" NPT while the old heads were tapped for 1/2" NPT (like my OEM sender).

I noted that the water pump has what appears to be a 1/2" NPT fitting in the top. Would this be a good location for the temp sender (better than the intake manifold)? Am concerned as the sender is right under the coolant hose that goes to/comes from the radiator and I suspect the hot radiator hose may be influencing the readings (too high). The upper radiator hose practically rests on the top of the sensor (hardly a hair's gap between the wire connector and bottom of the radiator hose). I'm tempted to move the sender to the water pump just to see if there is an improvement. Nothing interfering down there, smack dab on the top of the water pump and no hoses passing over or near it.

Or, would it be better to position the sender in the crown of the radiator hose neck/coolant fitting that attaches to the intake manifold (contains the thermostat)? I removed the thermal sensors (2) that were in the intake radiator hose neck/coolant housing and replaced with NPT plugs. I think one of them is 1/2" and the other is 3/8" (hoping upon hopes).

Advice welcome! :seeya


[Modified by TedH, 10:22 PM 5/25/2002]

 

The first thing I would do is recheck the valve settings. A tight exhaust valve could cause both the overheating and the erratic idle. A vacumn leak could also cause both those symtoms. You may want to take a vacumn reading to see what it is.

I would not put the temp sender in the water pump. There it would be reading the coolant before it went into the engine instead of as it exit the engine as it does being in the intake manifold. The radiator hose being close to the sender will not affect the reading. I would only change it if there is a possibility that it could rub on the hose and wear through.

You may want to get a mechanical water temp gauge and install it temperarily to see if the sender and gauge are reading correctly.

How long does it take to get to those temperatures?


[Modified by Pete79L82, 10:41 PM 5/25/2002]

 

Ted,
I have the sender in the Edelbrock intake too. I have a Gm replacement motor form 1980 and the head hole was too small also. It has always read correctly in the intake. I used a calibrated digital thermometer we use at work to confirm it. I would check this first tobe sure it's reading right, then move on. I had a problem last year with the carb being too lean,once rejetted it was fine.
Gary

 

Takes about 15 minutes to get to those temps. It gets to 220 in about 10 minutes from start. I'm going to try adjusting the rockers again today (with engine warmed up and running, gonna be messy!). I also have guide plates and I suspect pushrods may be getting a little close to the head castings (really close tolerances on the pushrod-to-head-relationship).

 

I reset the lifter pre-load/lash on both cylinder heads. Needed some adjustment on #1 and #2 for sure. I just backed the timing off too. It was WAY too advanced. Now is set at 10 degrees BTDC with the trans in Park and advance disconnected/plugged. I'm hoping those measures will help my cause a little.

Next on my list is adjust mixture using the vacuum gauge. My temp sender 'blade' broke off today. I had bent it down flat to clear the radiator hose (that passes just over it on the intake manifold). I suspect that is part of the reason for the high temp readings but I'm going to be cautious until I get a new sender installed (may also install a mechanical sender/gauge into the cylinder head until the new sender arrives just to verify temps).

Mixture is the last item that I have to check (without tearing the valvetrain/heads down to look for potential causes). The engine seems to be settling down a little bit now that timing has been adjusted.

I wouldn't be sprised if I was getting near 16 degrees of 'base' timing (without advance) at/near idle. Could that cause high temps? One thing I noted when I shut the car down after trimming the timing back was a mild backfire; sort of the sound of raw gas igniting in the lower exhaust system. No bang; more of a burp/gurgle. Not sure what that indicates but mixture and the mechanical temp sender are next once the engine cools...

Keep that advice coming!!!

:seeya

 

An overheating condition could have been from valves adjustment that is too tight, also 16 degrees of advance would cause some problems too. As for the "burp/gurgle" you may want to lean your baby over your shoulder and pat it on the back.

Keep us posted.

 

Once I figured the temp sender out, I added some of that base advance back in since the car was wanting to diesel on shut-off and just wasn't sounding 'right' with the timing retarded. That also resolved that burp/gurgle in the pipes.