Engine cuts off when thermostat opens???

Dont know if yall will remember me or not, i have a 1975 Cj5 that im fixing up. I have finally gotten the replacement rear end in, changed the rusted out headers, numerous other things. all is left is roll bar, windshield, seats, doors, top, and wiring. so almost done.
I am having the wierdest problem though, whenever i run the motor (fuel pump, ignition, and something else straight to the battery) it runs fine until the temp runs up to 180-200, where the thermostat opens. It cuts off as soon as the thermostat opens. i had the radiator open to make sure the water pump was working properly, ran fine till the second that water started moving, then motor shut off. that makes no sense whatever to me. Im really hoping that someone can help me out with it. my mechanic friend has no idea either.

David

 

What motor is in that jeep?

304?

The only thing I would see that could cause that type of problem would be an issue with the heated choke circuit. maybe.

 

Still have the Prestolite ignition?

 

I wonder if the TCS system is taking effect. Maybe inducing a vacuum leak that is otherwise closed off by the CTS. Or working normally and disabling vacuum advance once it is at temperature. try routing vacuum advance actuator directly to ported vacuum and see what happens.

 

It has the 258 straight six, offenhouser intake with 4bbl holly. as far as i can tell it still has the stock ignition. as far as the tcs and cts...i have no idea what you are refering to lol.

"try routing vacuum advance actuator directly to ported vacuum and see what happens"

Ill try that as soon as i find out what that means in english. i have some schematics ill check out and find out if there are any vacuum problems. If it ever quits raining. forcast says its raining all this week. im hoping its wrong. im almost to drivable and am itching to get it done.

David

 

TCS = transmission controlled spark. Cuts out the vacuum advance in top gear. Controlled by a switch on top of the transmission, connected to a solenoid on the engine. I think CTS is a typo for TCS.

There is a vacuum nipple on the distributor. You can remove the existing hose, plug it, and run another hose directly to the vacuum tap at the base of the carburetor. That will bypass any vacuum switches that might be turning on and off.

 

CTS is coolant temp switch, the thing on manifold, engine block and/or thermostat housing with vacuum ports that open and close with coolant temp. The one on the thermostat housing would stay cool until thermostat opens, then whatever vacuum function is plumbed through it would be affected. Bypass the CTS and see if the problem goes away. Or it will be bad all of the time. but it will help you figure out the problem.

A service manual (not Chilton or Haines) will help you to understand the lingo better.

 

Ah. Jeep calls CTS a CTO (coolant temperature override).

So TCS is a typo for CTS? Or did you mean TCS?

TCS could still be applicable.

 

Also, a '75 will have the Prestolite electronic ignition from the factory. The easiest identification for Prestolite is by the plastic vacuum advance canister on the distributor. All other apps will have a steel canister.

The Prestolite ECU is a gold (usually) box on the inner fender. This ECU is known for being temperature sensitive. You can be driving along and the engine will quit, like you turned off the key. Then you'll pull over put the hood up, look around, close the hood, and the engine starts and you drive off.

 

What I called the CTS is indeed the coolant temp override switch. CTO switch could be the problem, or some other part of the TCS system. If the problem happens when the CTO gets hot it is likely that the CTO switch is actually functioning correctly bu causing a vacuum leak or causing the engine to retard too much. If the entire TCS system was operating correctly this woul likely not be a problem. But if TCS retards timing even when engine/ambient conditions should not allow it then you would have trouble. Just bypass it and see if your problem goes away.

 

Ok, so when its not raining i'll go and check the vacuum hoses first. it would be pretty simple if all it is is a vacuum leak. that and wiring should take care of it then?

 

What I'm suggesting is routing a new piece of vacuum line from either ported vacuum (right side base of carb) or manifold vacuum (a vacuun nipple screwed into yje manifold somewhere) to the vacuum advance actuator on the distributer. All of the OEM stuff between the vacuum source and the vacuum advance actuator was added the reduce hydrocarbon emissions. At best when everything is working properly you will sacrifice throttle response and pulling power in top gear. At worst...well, you know all about it.

Chilly

 

i took a quick look through the motor, the only vacuum line at all is one that goes nowhere from the carb. no other lines anywhere. PO's are the devil

 

Can you snap a pic of the carb, manifold and distributor?

 

It would take a huge vacuum leak to stall the engine, I don't think thats your problem. Also, losing vacuum to the distributor will not kill the engine either, I would say your problem is somewhere in the ignition side of things.

 

With regard to the CTO, This switch has both manifold and ported vacuum hooked to it and a line to the dist vac unit. When the engine is cold the switch allows full manifold vacuum to the dist vac unit, this increases cold engine idle speed by advancing the spark.
When operating temperature is reached the switch moves from manifold to ported vacuum to the dist.
If someone inadvertently set the timing on the engine while it was cold and the switch was sending manifold vacuum to the dist when it warmed up and the switch moved to ported vacuum its possible the engine could stall ( depending on initial timing ) as the timing would suddenly be retarded 12 - 15 degrees.

It may be woth disconnecting the dist vac line and check the timing before the engine reaches operating temperature.

Its easy to get the manifold and ported lines on these switches reversed wich will lead to timing problems, I have helped many that had no power at speed and under hard acceleration and engines running hot by the lines being reversed on the CTO resulting in the initial timing being set with manifold vac applied to the dist, Soon as your on the throttle and loose the high manifold vac the timing retards.

 

Timing should be set with vacuum line disconnected from distributor and plugged. And when vacuum drops under load the dist SHOULD retard. That's what it's all about. That's why it's there.

The ideal setup for vacuum advance is to run manifold vacuum to the dist with no bullcrap between. Ported vacuum, CTO switches, top gear switches, vacuum solenoids, all of that crap is designed to retard the timing from nominal to reduce hydrocarbon emissions. Now, the designers were not total jerks so they only hindered performance when you thought you wouldn't mind or notice. So the TCS system doesn't screw with your timing unless:

1. ambient temp is above 60-deg
2. engine is up to normal operating temp (160 for V8)
3. tranny is in top gear

That's the idea of how it works, and if your TCS junk is all working OK I guess one might be able to tolerate the de-tuning. However, lets say the rest of the TCS system isn't working right or is no longer connected right. There is no telling how it will affect performance. If we knew how it was screwed up we could speculate. But that's interesting for an academic discussion. Instead, just connect manifold vacuum or ported vacuum to the dist and see how it works. I recommend full manifold vacuum to the dist with no other baloney in between. If you can't find manifold vacuum ported vacuum isn't a bad compromise.

 

I totally agree that the dist vacuum advance timing SHOULD retard under loss of manifold vacuum whether it be ported or straight off the manifold, My concern was that at some point the initial mechanical advance timing could have been inadvertently set with manifold vacuum applied to the dist ( vacuum to CTO incorrectly routed or set on a cold engine ) wich would result in the initial mechanical timing being 10-15 degrees to late. The engine may not idle well that retarded.

I agree that timing should be set with dist vacuum line off and plugged.

 

So it could be cutting off because there are no vacuum lines attached to anything. If i am understanding right i should run a vacuum from the headers to the distributor. that could stop my problem. I'll do that next. You guys are a lot of help, i really appreciate it.
Now if i could get one of yall to make it stop raining that would be awesome.
David

 

Not headers. Intake manifold.