Alternator issue?

[alexmak]

On Sunday, I was driving our roadster home from Cars and Coffee when I noticed the coolant temperature gauge climbing over 100°C. Simultaneously, the oil pressure gauge dropped to 20, and the voltage gauge behaved erratically. Concerned, I pulled over, turned off the engine, and inspected everything. There were no leaks or visible issues, except that the radiator fluid was obviously too hot. It appeared that the radiator fan wasn't spinning either.

Attempting to restart the car proved futile due to a seriously discharged battery—around 6V, if I recall correctly. I jump-started the car from a spare battery, and while the engine started normally, the cooling fluid remained too hot, and the radiator fan refused to engage. I drove home cautiously, about 7-8 minutes away, monitoring the gauges, which were behaving wildly. The speedometer even did a 360-degree spin several times—classic signs of a discharged battery.

The following day, I fully charged the car battery, registering 13V on the voltmeter. Starting the car revealed normal behavior from all gauges, with the radiator fan activating around 85°C. However, upon measuring the battery, it showed only 12.5-12.7V—indicative of a potential issue with the alternator. I expected at least 13.5V-14V. The same readings were observed at the alternator's terminal.

Conducting a "backyard mechanic" test, I disconnected the battery's positive terminal while the engine was running. The engine immediately died. To my inexperienced eye, these indicators point towards an alternator issue. Before reaching out to Blueprint regarding this problem, are there any other signs or tests I can perform to isolate the issue or confirm that it's indeed related to the alternator? Pardon my probably not always correct terminology.

PS just in case, it's a carburetor engine from BPE, with a single wire alternator.

[Norm B]

Check the “ one wire” for continuity. Some have a 100 amp fusible link in them. There also could be a bad connection or connector at the alternator or battery.

Norm

[Mastertech5]

It's the alternator. If it's not charging your gauge will read battery voltage and slowly go lower as the battery discharges. You took the battery out of the equation by disconnecting it, so bad alternator. I'm surprised it ran at all with the voltage so low. The alternator must be charging a little. 13.6 V minimum is what I've always gone by.

Make checks as NormB suggests first, good points!

[alexmak]

Check the “ one wire” for continuity. Some have a 100 amp fusible link in them. There also could be a bad connection or connector at the alternator or battery.

Norm

thank you, Norm! I disconnected the terminal on the alternator and connected it back to make sure there's a good contact there. From the harness diagram it looks like the wire just goes to starter solenoid, but I vaguely remember that wire under the dash for some reason?

[Rdone585]

You can remove the alternator and take it to an auto parts store. Most will test it for free, or at least they use to.

[Ted G]

I had a similar issue about a month ago. I was using my timing light and connected the wires on the timing light to a good ground point, and the positive to the back of the alternator. Apparently, I must have hit the housing when removing the timing light and burnt my 100 amp fuse in between the alternator and battery. The reason I used the alternator post was I wasn't happy with running my wire all the way across the engine bay to my only positive post. Since then, I added a positive post on the passenger side for this reason.


Needless to say, I went for a drive and slowly saw my voltage gauge drop. Thought is was an alternator problem, but finally realized it was the fuse.

Replaced the fuse and good ever since.

[alexmak]

You can remove the alternator and take it to an auto parts store. Most will test it for free, or at least they use to.

Yes, very much planning to do so, as soon as I figure out how to remove it :) (having bought the engine from BPE and never dealing with a belt, I'm a bit perplexed how to do it)

[Norm B]

Check the continuity between the alternator and the starter solenoid post. I have the a copy of the Breeze front battery setup and my alternator wire runs directly to the battery post. I had the crimp on the connector at the alternator fail. Had that wire “professionally” made and the wire pulled out of the crimp at the alternator. It was hidden under heat shrink which didn’t help the trouble shooting. Took the alternator to a shop for testing and it passed fine.
If the wire passes then, having the alternator tested is your next step.

Norm

[egchewy79]

Yes, very much planning to do so, as soon as I figure out how to remove it :) (having bought the engine from BPE and never dealing with a belt, I'm a bit perplexed how to do it)

There should be some type of threaded tensioner that can be relaxed to allow for the belt tension to be released

[alexmak]

There should be some type of threaded tensioner that can be relaxed to allow for the belt tension to be released

yep, there's such thing. I will research into this more, thank you

[alexmak]

spoiler alert: it was the alternator!
(at least the tests in two stores showed that)

[Norm B]

Thanks for posting the findings. Don’t know about others on the forum but, for some reason it bugs me when a resolution to a thread is not posted.

Norm