CUCV 1986 M1008 - In a Real Pickle - Bad Heads - Need Advice

The water temperature sensor is in the left drivers side head up front. Make sure you do NOT have a glow plug wire hooked to the temperature sensor. I seen this before. The wires are both green. In stock you can not hook up the glow plug wire to the sensor but when you cut the stock 3/16" spades off and put 1/4" spades on. You run that risk during reassembly of the harness after head removal. Just a thought. Never happened to me but I have fixed a few that had the wires hooked up incorrectly. That light that is lit is the sail boat in the Red sea light. Can you see that is the light? Good Luck. But I always send my alternators out for overhaul. There is more to an alternator and starter then just putting a few new parts in. If NOT the rebuilder up my way sure spent a lot of $$$$ on nonsense. Not everyone is as talented as they act. Have Great Day.

cucvrus said:

The water temperature sensor is in the left drivers side head up front. Make sure you do NOT have a glow plug wire hooked to the temperature sensor. I seen this before. The wires are both green. In stock you can not hook up the glow plug wire to the sensor but when you cut the stock 3/16" spades off and put 1/4" spades on. You run that risk during reassembly of the harness after head removal. Just a thought. Never happened to me but I have fixed a few that had the wires hooked up incorrectly. That light that is lit is the sail boat in the Red sea light. Can you see that is the light? Good Luck. But I always send my alternators out for overhaul. There is more to an alternator and starter then just putting a few new parts in. If NOT the rebuilder up my way sure spent a lot of $$$$ on nonsense. Not everyone is as talented as they act. Have Great Day.

Click to expand...

Hey Cucvrus!
Hummm..... from what I had found online, the temp light went to the sensor in the radiator... so now from what you're telling me thats the wrong sensor, and is instead the one in the drivers head. Guess thats why replacing the wrong sensor didn't help...

As to the sensor in the front side of the drivers head, I did notice that all the wires were green, which in my openion is kind of dumb on GM's part... but in any case, this truck did have multiple electrical issues when we bought it. Someone had hacked parts of the harness, and most electrical ends had been replaced but done so with only "crimp" connectors and apparently someone who didn't know how to use them, as many wires would just pull out of the connector. I had to redo a lot of the wiring back 6 years ago when we got this truck. And I do remember replacing all the glow plug wire terminals, however I did replace them with the actual correct GP connectors... but there was one of the new connectors that did break off, or at least the plastic broke off, can't remember if I had to replace the terminal again or not.

I'll have to look at the wires again, see if its possible to hook up the wrong wire, depending if I had to change the connector or not.
If the connector has been changed, is there any way to tell that wire from a gp wire??
**(EDIT: I figured it out with a voltage meter, turn ignition on and watch for the voltage to drop when the GP relay kicked off. If it dropped, then I knew it was a GP wire. The sensor wire didn't drop and showed 12v instead of 10.5v)
Or maybe the sensor just crapped out guess it would help if I replaced the right sensor.

As far as the alternator goes, I'm not sure whats the issue there, it was working fine before. I believe I have the wires connected to the back correctly, unfortunately all 3 wires are All red, so it makes it a little hard. One solid red wire about 6 inches from the end, is joined to a red wire with a white stripe. The other two are solid red for as much of them as I can see.

I believe the 2 solid red wires goes to the "batt" terminal, and the red wire with the white stripe I believe goes to the other terminal.... ??
Something else to try to figure out today.

Ok... i "fixed" the temp sensor...
you were right Cucvrus... I had switched the temp sensors wire with a gp wire...
the only gp wire that I had to repair for a 2nd time because the actual GP terminal broke again, and I had to replace it with a regular spade receiver terminal.
on to other matters...


QUESTION: Could a bad battery cause an alternator to overcharge??
I'm not sure that these batteries are bad, they are interstates (which are NOT the quality they used to be...) and they are about 6 years old. They did run down quite quickly when we were trying to bleed the fuel system with the old IP that ended up being bad.

I have two alternator rebuild kits that I was saving... but I guess I could go ahead and use them if they're needed. With that said, if nothing is wrong with the alternator, then I don't want to waste these kits.

Always check your batteries with a good load tester and take any guess work out of the picture. If those are 6 years old they would be suspect.

royalflush55 said:

Always check your batteries with a good load tester and take any guess work out of the picture. If those are 6 years old they would be suspect.

Click to expand...

I have an old style "heater coil" mechanical battery load tester. I'll test them when I get back to the truck and see what it shows.

Ok, Tested the batteries, both showed around 1000 cranking amps under "tester load". Which 1000ca is their rating.
So even though they are 6 years old, the batteries seem ok.

I took my voltage tester and checked the drivers side alternator, it showed about 14 volts or just over, which should be about right for one alternator.
But the passengers side alternator instead of showing 28-29 volts, it still shows 31.5 or so volts coming out of it. So about +2.5 volts too high.

So.... it looks like it could be the voltage regulator in the passenger side alternator or something.
I may have to rebuild this alternator and go from there.

Here's a separate question:
Has anyone heard of a "CHEVY DELCO ALTERNATOR HARNESS ANTI- FEEDBACK DIODE wire" for the 27si alternator?

Now, I'm no electrician (but I have learned a lot through the years repairing all kinds of stuff), but I do understand that a diode is basically a "one way electrical check valve", when its placed inline in a circuit, and that is exactly what the title of these things sounds like.
I've seen these for sale a few times, and was curious if these CUCV's needed this "upgrade"? Or is that only needed on civy models?? or???

Thanks All

well of course i had to screw up something right at the last thing that I needed to fix to have the truck back up fully functional...
blew a hole in the back of the alternator casing trying to install the new "capped" bearing....

I don't have a press or anything like that, so I put the bearing in the freezer for a while, got the old bearing out, went to install the new bearing just like I did with the front (pulley side) bearing (which I had removed and reinstalled the old front bearing several times already in recent weeks without issue...) but of course tapping it in with a block of wood, while the case was supported, just was "too much" for that cheap thin junk pot metal alloy to handle...

guess its off to look on ebay for a case...

EDIT:
Will a "regular" 27si alternator case work? I think I read somewhere that it would.... but seems like I remember that a hole has to be drilled in it for something...??

That is exactly why I leave certain work to qualified professionals. I can do the hard grunt work all day. I can fix things others throw away and build things other are envious of. But when it comes to transmissions, Transfer cases, starters, alternators, differentials, and injection pumps. I let my money do the repairs and get back at doing the work that others seem to pass by. Keeping the appearance good IMHO is more important then redesigning the working system. How much do you save if you break things and they are a constant threat of questionable failure? I break things but most times it is an easy fix. Good Luck. I enough rebuilt alternators and starters to last till the next millennial. I have no interest in being able to rebuild the components. At my age I am happy to just go out and do the heavy grunt work with my Little Bull.

well, if I had a press it would be much easier and safer on the casing. I may just build me a press, could've used one a few times.... just need a place to sit it when its not in use.

in any case, I may check with a local guy who may have a case. If not I'll buy one off ebay. If I had taken my time a little more, I wouldn't have broke it.

Commander5993, Stay with it and you will succeed. At least you are learning how to work on all the components and you will have the satisfaction of knowing what parts are installed into them and how they work and perform.

cucvrus said:

I went thru 3 sets of heads before I found a good un-cracked set. I would say just put a good set of heads on the bottom end and call it a day. The head gaskets on most of these trucks are in bad shape if you still have the original ones. Time and wear have contributed to the head gasket leaking. I would not worry about doing anything else. The original motor has black silicone valve cover sealant with no gaskets. Check out a few of my threads. I have been changing head gaskets and having heads redone on CUCV's as regular maintenance items the past 3 years. Even good running supposedly nothing wrong with them had bad gaskets when I pulled the heads. 30 years and acidic antifreeze have that tendency.View attachment 683221This is a head gasket that was NOT leaking. I removed the heads just to change the gaskets as a maintenance item while I was rebuilding the truck. Glad I did. Look at the corrosion in the gaskets at the water passages. All I did was send the heads out and it took 3 sets to get a good set. I bought a complete gasket set and changed the head bolts. It has worked for me on everyone I worked on so far. I have not had any bottom end problems with any 6.2 even a few with over 200K on them. I have sold a few with over 150K and as far as I know they are running fine never been apart. Other then an injection pump or 2. My vote would be just change the heads and fix the problem. keep it with in budget. You know what you have fix what is wrong with it and move on. I just find pulling the engine and working on it on the floor is much easier. Disassemble it reseal it clean it paint it and reinstall it. that easy. Don't buy any unknown engines. they may have bad head gasket very soon just like yours. IMHO fix yours.

Click to expand...

Looks like I might have to have new heads. Do you have any experence with new aftermarket heads and where they can be purchased?

How about just an entire long block assembly? But if it were me I would find a set of used heads. Just get them checked for acceptable cracks. Some cracks are normal. Most all have minor cracks in the pre chambers. That area is replaceable. Have you had them checked at a reputable automotive machine shop?

ranger1950 said:

Looks like I might have to have new heads. Do you have any experence with new aftermarket heads and where they can be purchased?

Click to expand...

I bought a set a few years back.
6.2 Liter GM Diesel Cylinder Head for HMMWV and CUCV equipped with 6.2 Liter Diesel Engine (easternsurplus.net)

My local engine rebuild shop got me two 6.5 heads for around $800. They work great. I was too cheap to get the 6.5 injector lines so I massaged my 6.2 lines with a tubing bender, they work..........for now.
On another note, I knew that using exhaust manifold gaskets was the leading cause of blown exhaust manifold gaskets so, don't use any.
But I did not know about using valve cover silicone instead of the cork, which are the reason valve cover bolts always seem to be loose.
That's probably why my 69 beetle had spring steel wire bars to keep the valve covers snug. Why are the Germans so savvy with stuff like that?

wow... forgot this thread... five years ago... I need to read through it just to see what I have done to the truck before, as I have forgotten a lot of it now.

just so I don't continue to leave this thread hanging... I did end up replacing the heads with reman 6.5 heads, can't remember now how much they cost at the time. But I think it was about $600 or so. Also got a bunch of other parts, including new head bolts, reman injectors, glow plugs, and other stuff I can't remember. Heads and etc have all worked thus far, hope they continue to for a long time.
The "new" fuel return hoses that I installed at that time, went bad about a year after this. Thought my head gasket blew again the way the truck started chugging and such, and it was enough diesel on the engine to look like antifreeze. After that mishap, I replaced the oem rubber return hoses with silicone fuel line, and its worked perfect ever since.

Got issues with the temp light and coolant light AGAIN . This is the second time since this thread. Just replaced both sensors again a couple months ago, seems like it is a different issue this time.

Also just recently had to replace the glow plugs again, this is the 2nd time since this thread if I remember right. Found 3 bad plugs in jan, was going to just replace the three with some other "old good" plugs I still had. But ended up finding a whole set of brand new AC Delco plugs that I had forgot about buying. Installed those. Although the previous plugs were also AC Delcos too... not sure why they are burning out so quickly. I think I read one time that there was something that could "go bad" and send 24v to the plugs instead of 12v. I was thinking about this earlier today, will use a meter to test for that just in case.

can't remember if the starter was in this thread, but I just had to replace the starter again. Instead of getting another parts store reman special.. I got a Wilson gear reduction starter this time. Starts quick and easier to install. Just remember to change the starter bracket to one specifically made for the gear reduction starter. If not you can damage the block, see FAQ's and many other threads concerning that.

Did a whole bunch of other work in the last 2.5 months. but that is on other threads. here is two if anyone is interested.


hijacked an older thread here concerning fuel gauge and sending unit, my posts start at #15

A note on the injector return lines, the OEM lines are Viton rubber, they will outlast the engine. Aftermarket lines are buna-n rubber and these are the ones that get hard and crack after about a year. I am starting to see aftermarket kits in Viton. You can also buy 1/8 Viton tubing and make your own. Silicone rubber will last like Viton in this application but is permeable and will seep fuel constantly.

Also, throw those little clamps in the trash.

87cr250r said:

A note on the injector return lines, the OEM lines are Viton rubber, they will outlast the engine. Aftermarket lines are buna-n rubber and these are the ones that get hard and crack after about a year. I am starting to see aftermarket kits in Viton. You can also buy 1/8 Viton tubing and make your own. Silicone rubber will last like Viton in this application but is permeable and will seep fuel constantly.

Also, throw those little clamps in the trash.

Click to expand...

Well the original one's were cracked and splitting at the connection points where the clamps were. The first "new" one's I put on were the actual OEM kit. I don't know if they were NOS or what, but they didn't last.

I did not know that silicone rubber was permeable. Thanks for the info I'll try to see if I can find some Viton tubing.

87cr250r said:

A note on the injector return lines, the OEM lines are Viton rubber, they will outlast the engine. Aftermarket lines are buna-n rubber and these are the ones that get hard and crack after about a year. I am starting to see aftermarket kits in Viton. You can also buy 1/8 Viton tubing and make your own. Silicone rubber will last like Viton in this application but is permeable and will seep fuel constantly.

Also, throw those little clamps in the trash.

Click to expand...

Well, I'm glad you brought this up about the return lines. Instead of a coolant leak, I found I had diesel fuel leak. It was the main return line connected to the hardline on the passengers side. I had bought some UV dye and put it in the coolant system, a couple days later I drove to town and back. Got my UV light to see if I could find the coolant leak, the dye was supposed to light up bright green (although the dye in the bottle was orange ) In any case, didn't see anything with either of those colors, but when I began to look on the passengers side, I saw something dripping that lit up with a blue hue. It was dripping off the fuel return line, and sure enough it was diesel fuel. Didn't know Diesel was reactive to UV light, and I had not been able to see this before with just a regular flashlight. Got down and looked on the frame, and yep it was blue too. So that was my leak.

I pulled that return line yesterday, and that silicone hose had cracks all through it. I have never seen one of these hoses do that before, and I have used them for fuel lines on all sorts of things for some years now. I got to looking at the rest, and could clearly see they have cracks all through them too.

I've been looking for another fuel return kit, but only found dorman. Which is only listed as being "rubber", and its the same kit I bought back in 2017 (found my order) and it didn't last no time.

I've also looked for Viton (aka Fluoroelastomer) hose by the foot, and have found some. But looks like about $50 w/shipping is about the cheapest for 10 ft. I know thats a little longer than I need though. Also I'm not sure what I would do about the caps for the last two injectors, as even some other kits I have found don't come with the caps.

I installed Viton return lines in my diesel VW pickup, and cut an inch section that I plugged with a small bolt and hose clamp to replace the rubber caps. Never had any issues so far. I got the lines from McMaster-carr, they were something like $3.75 a foot in the size I needed. Hopefully that’s helpful for you! Really liked reading your thread so far, it’s great to see all the successes you’ve had on this truck, despite the consistent issues… but constant work is what keeps us sharp.