I had none of the typical symptoms of a blown head gasket either... the oil was clean, no steam, started and ran nicely (except to the first 5 min of a cold start, which I'm still trying to diagnose). I DID have a loss of coolant, and the symptoms were very much as you describe on your rig. When I removed the head I was AMAZED that the truck ran as well as it did... and I also passed emission testing here in NJ with flying colors... in fact, TOO GOOD! The guy tested it twice cuz he thought something was wrong with the results. I now am thinking that maybe the glycol that was evaporated in the exhaust stream may have been playing games with his machine.

The temp sensor is VERY easy to check! Get an el cheapo ohmmeter and pull the connector on the fender well and test the thing! How far are you from Tinton Falls ? You are welcome to come down here and use my ohmmeter if you don't wanna buy one.

I think yer runnin' around in circles with your diagnosis... do a compression check also... I was gonna suggest a head gasket problem myself, but didn't wanna be the bearer of bad news, but the more I think about it, the more I believe that may be the case... possibly in ADDITION to other troubles with your throttle body.

Good Luck!
Jeff

OK, that's two votes for compression check. It hasn't been losing coolant, but this overheating issue that's cropped up in the past month makes me wonder. Normal driving around town is fine. It's only when I get on the hi-way for an hour that the temperature climbs. I was figuring with 450,000 miles and original rings that top cylinder lubrication is probably not happening at this stage (time for the 50 w oil in the crank case). The head is the original factory head and baby this one's been beat. The last time I had it off one exhaust valve had a hole burnt right through it and another had the seat melting into the head; and it still ranà Lot's of hydrocarbon in the emissions though. The shop that reworked it did an amazing job replacing that valve seat. I thought the head was done for, but that was five years and a lot of miles ago. I know how tough it is to kill these engines. They may not run well all the time, but they keep running. I'll do a compression test this weekend and post the results. IÆve got a multi-tester so IÆll check the resistance on the temp sensor too. Thanks for all the feedback and advice.

It might pay to pull the radiator and have it flow tested. I found that mine was about half plugged up. It was fine around town with little load on the engine, but continuous use on the highway it would heat up some.

My coolant loss was not very evident by looking at the overflow reservoir... I didn't realize I actually had a problem with coolant loss until I started opening the radiator at lunchtime at work after the engine cooled. It seems that coolant leaking into #4 cylinder on the intake stroke was being replaced by combustion gases on the compression stroke. (at least that's what I _think_ was happening!) The level in the overflow would stay somewhat constant... but a look into the radiator revealed that the level was about an inch down after a 10 mile trip. The story of how I discovered the problem is actually much longer than this, but the point is to not trust the reservoir as an indication of coolant in the system.

Keep us posted...

I'll be adjusting my valves and re-torquing my head this weekend. I ran a bottle of injector cleaner into the gas tank and filled up on Sunday. I think my cold idle problem is somewhat improved, but it's probably too soon to be certain. I'm planning on cleaning out the TB this weekend when she's torn down for the other work... (fingers crossed)

QUESTION: On the throttle body idle air bleed adjustment screw... is it "safe" to remove that completely, and squirt some cleaner down there from the screw hole ?

C/YA!
Jeff

I may be in the same boat as you (now just to figure out what that boat is <img src="/forums/images/graemlins/notooth.gif" alt="" /> ). During a cold start, my truck starts just fine... but then stumbles and tries to die and I have to play with the throttle for appx. 30-60 seconds. After that, it runs/drives just fine and will continue to start and run fine until it has been sitting for a few hours. The only difference is that my idle is fine. Been working too much to check into it... but its getting worse so I need to find time <img src="/forums/images/graemlins/scared.gif" alt="" />

lots of interesting stuff here. glad my pic helped you w/EGR, even though it was not the culprit.

what is the condition of your fuel system? filter is good? injectors ever been cleaned? pump is fully operational? FPR? while doing a compression test it may be a good idea to check fuel pressure.

overheating: how about t-stat, & you ever flushed the block?

Sean, your symptoms are EXACTLY what I've been having for the past six months or so. Once it runs for 2 minutes, it's fine. If you do find something, let me know, as I've ruled out the temp sensor and the AAV ... I did spray some cleaner down the TB throat and it seems to have improved... well, maybe _changed_ the symptoms a bit. I was gonna pull the TB today and clean it out real good, but the gaskets didn't come, so will have to be next weekend. I'll clean out the EGR ports at the same time.

C/YA!
JB

Well, I have already ruled out the fuel pressure regulator. The symptoms seemed to be pointing that direction at first, so I put a new one on last weekend. Didn't do a thing to help. Its odd because this is not something that seemed to onset gradually... it just started doing it one day and has gotten progressively worse over the past 3 weeks <img src="/forums/images/graemlins/confused.gif" alt="" />

Thanks to Pucci for letting me know how to post pics!

This is the easy way to measure the ECM temp sensor, and will also verify that wires from this harness connector to the sensor are good.

My truck is an 88 Troop... I don't know if the wire colors or connector location will be the same on your rig. This connector is the larger of the two on the bracket on the passenger side fender well, right behind the battery.

These two wires, Black and Green/Yellow




Check cold first, use the temp/ohms chart that's been posted previously in this thread. Put a thermometer in the radiator, or use an infrared thermometer. (the radiator may be a few degrees cooler than the engine at this point...) Put the cap back on, plug the connector back in, and run the truck till it gets up to temp. Stop the truck, pull the connector and hook up your ohmmeter. You should read around 200-400 ohms. Check the meter from time to time as the engine cools. The resistance should slowly climb back to the first cold reading as the engine cools off.

C/YA!
JB

Excellent pics. On the '89 P'up there are two connectors the same size but the upper is blue and the lower one black. The wires are as you described in the lower (black) connector and the temp sensor tested fine; 1.8K at ambient air temp (90 degrees at the time) down to .28K when the engine was warmed up.

The compression test was a little less positive.

#1 - 170
#2 - 160
#3 - 145
#4 - 170

A squirt of oil raised the pressure in #3 to 150. A comparable squirt did nothing to raise the pressure in #2 so, Mr. Paget, you are correct sir. Now the question is how much more money do I want to put into a 16 year old rust bucket approaching the half million mile mark...?

Anyway, knowing from past experience that it will run forever (short of hydro-locking) I'll do some watchful waiting, stay off the hi-way and repeat the test in a few weeks to see how fast it's deteriorating. Thanks to all for the tips.

With those compression numbers, my guess is that you may have a burned valve, but PROBABLY not a blown head gasket or cracked head. More likely, given the change with the oil, it is rings bad.