Info needed: 1967 M38A1 Lubrication?

[rob love]

1: It should not have. The first filter is on the suction side so does not effect the output pressure. And it does not take 7 psi to flow through the filter. Most likely your system was just re-priming itself or there was some dirt in the checkvalves. A person only blows at about 3 or 4 psi...if you can blow thru the filter, the the fuel pump should be able to.

160 is actually the closing temp of a thermostat rather than the opening temp. Opening temp can be 180 or even higher. So likely that is the temp that the coolant opened, or it has not even opened yet, and so is maintaining that temp with no work being performed. If the thermostat is still closed, then it is just the flow from the bypass hose (maybe a 7/16 hole) that is allowing some level of flow.

Drive it and you should see the temp come down to the 160.

[Les Kovacs]

Hi Rob.....thanks for the quick response....wow what a learning experience!

OK....so here is what happened after an actual 25 min drive at about +27 C and moderate humidity....the temp gauge slowly went to about 185 degrees (temp lingered at around 165 for longest time)and stayed there through the whole drive....after garaging the jeep....I checked the upper rad hose...no pressure so I opened up the rad cap and put in a temp gauge....rad coolant read +155 F....Question....is +185 F normal for average summer drive and why was the actual coolant at +155 F?.....also, why did the new thermostat not open?.....is temp gauge reading dubious?

PS...Temp gauge does not fog up any more since putting in a thermostat.

PS...rad cap is dubious as it is old and I had to put in a rubber gasket that was made out of bike tire inner tube. I have no clue what the PSI rating is!

I am ordering two new rad caps....Kaiser Willys shows that a 7 lb cap is required for the M38A1 but the 1967 CDN military manual states that a 4 lb cap is required.

What's the correct rad cap for this jeep?

Thanks.....les

[rob love]

185 is not normal. It doesn't hurt mind you, but it is not normal.

Any chance the problem is in your gauge or sending unit itself? Perhaps you do not have a problem with the actual coolant.

You could try and pull the sending unit, and replace it with one of those cheapy mechanical gauges from Cdn tire or princess auto and see what reading you get.

Otherwise, you have a circulation problem. One possibility is your antifreeze is over-strength (should be 60/40 mix). You already changed your water pump, so that isn't the problem. And the pressure of the cooling system is to merely raise the boiling point, and does not really effect cooling and flow. But if the gauge is at fault, perhaps that is why the last owner removed the thermostat as an attempt to repair a perceived "overheating" condition.

[Les Kovacs]

Thanks for the prompt response....can you please send me a picture of the temp gauge sending unit?...not sure where it is or what it looks like.....is it still available?

So, I can either use a 4 lb or 7 lb rad cap?

Can you also review the procedure to adjust the fuel mixture (new small additional tail pipe somewhat sooty after only 20 min drive)....what temp does the running jeep have to be...cold or operating temp.....

Thanks!

[rob love]

Temp sending unit is on the back right of the head.

I'll have to look the cap up at work today. Fours and sevens are the numbers most often mixed up by dyslexics, so you never trust either.

To adjust the fuel mixture, you have to have the engine idling at operating temperature. You turn the screw in until the engine starts to stumble (usually less than one turn left), then turn the srew slowly back out until you reach the highest RPM. If the engine does not stumble while being turned in, then you have a carb problem. DO NOT jam the screw with force all the way in, as you will damage the seat of the needle and ruin it. In the end the screw should be out about 1-1/2 turns. Ideally, it is set with an exhaust analyzer so you get the mixture right, but those are getting hard to find these days, since every new vehicle has that built in to the emissions systems.

[Les Kovacs]

Thanks for temp sending unit info....I will change out with gauge soon.

I just picked up a new 4 lb rad cap from Bay Auto here in Barrie. CDN2 manual states a 4 lb cap.....Kaiser Willy,s only sells a 7 lb cap.

Thanks for carb mixture info....I will adjust soon.

Took the jeep out again today.....+24C/sunny and humid (solar eclipse here in Barrie was a bust....not much change in lighting.) After 15 min driving-temp gauge showed a tick over 180 F....never moved after getting there. On my return home I immediately opened the hood, felt the upper rad hose (no pressure) so I pulled new rad cap and measured coolant temp....as yesterday at 155-160 F.....not sure how to interpret info....bad gauge?....sending unit? or both?

Please comment.

PS...for some reason your picture did not come through?

les

[rob love]

That's funny, I see the photo just fine. Google M-series temperature sending unit and lots of photos of it will come up.

I am sure there is a proper range of ohms that could be compared at various temps for both the gauge and the sending unit, but I can't tell you what they are. In the army, parts were cheap. We would just change whatever half was easiest, and if that didn't work, we would change the other part. A word of caution when working on the panel. It MUST be grounded before you turn on the ignition switch if you have it off the dash, or you will almost instantaneously burn out any or all of the gauges (oil, fuel or temp). Other vehicles like the M151 actually had a ground wire from the body to the dash,the M38a1 did not. The gauge case must be grounded. Too often, guys would test the gauges by putting power to the smooth connector, and ground to the ribbed connector. The needle might move back and forth, but the damage will be done.