4.3 Mercruiser operating temps? Overheating?

[jimmyc607]

Hello,
I have a 1990 Baja 190DSR boat with the 4.3 V6 in it. I just purchased the boat this spring and have had it out a few times this season. My question is related to the operating temp and whether or not the climbing temps I am seeing are normal?

When cruising at either high or low speed the boat is right around 175 degrees or so. It remains there and never really fluctuates much until I start to sit at an idle in the middle of the lake. Since I was not completely comfortable with making sure the boat would start right up for me we would just leave the boat idle in the middle while we hung our and drifted... but I noticed while doing this the temp would slowly climb up. I saw it get to around 220 at one time so I put the boat in gear and cruise slowly... the temp came right back down and remained at 175 degrees.

I did order a new outdrive water pump kit for it that I just got today because I figured it's probably never been changed or at least not recently. The impeller on the inside did have a few cracks but all the "fins" were in tact. I'm planning on taking the boat out again this weekend but just wanted to see if any of you guys might have anything else I should look for?

Thanks ahead!

 

[Bondo]

Re: 4.3 Mercruiser operating temps? Overheating?

I did order a new outdrive water pump kit for it that I just got today because I figured it's probably never been changed or at least not recently. The impeller on the inside did have a few cracks but all the "fins" were in tact.

Ayuh,.... Welcome Aboard,.... Sounds like ya caught it Just in time,... Those need changin' every year or two....

 

[Don S]

Re: 4.3 Mercruiser operating temps? Overheating?

Cracked vanes means they aren't pumping water, just going round and round doing nothing.


View attachment A1 Impeller replace.pdf

 

[jimmyc607]

Re: 4.3 Mercruiser operating temps? Overheating?

Thanks for the reply guys. I plan on putting the new water pump kit in tonight and then testing it out on the lake this weekend. Is there anything else I should look to replace in terms of the cooling system?

The previous owner pretty much just used the boat and really didn't do a ton of the routine maintenance that I plan to do.

 

[jimmyc607]

Re: 4.3 Mercruiser operating temps? Overheating?

Still having some overheating issues and I am completely stumped at this point so if anyone has any advice I would really appreciate it.

So far I have replaced the stern drive water pump/impeller, new 140 degree t-stat, and a new engine water pump and i'm still seeing the engine temps climb while i'm at idle in the water.

It takes a little bit but the temps will slowly climb up while sitting idling in the water... they have gotten up to about 200 before I shut the boat off or start to cruise. At idle cruising speed or while moving at all the temps almost immediately come back down to around 160F or so.

I'm not sure what else to check at this point?

 

[sharkin95]

Re: 4.3 Mercruiser operating temps? Overheating?

first buy a infrared temp gun ($25.00) check t-stat housing, risers, ex manifolds, next compression check all cylinders, post back results..

 

[jimmyc607]

Re: 4.3 Mercruiser operating temps? Overheating?

I will have to get an infrared heat gun as I don't have one but I did do a compression test a couple of weeks ago just for my own personal piece of mind and all cylinders checked out to be in spec and were even across the board.

 

[Bondo]

Re: 4.3 Mercruiser operating temps? Overheating?

Still having some overheating issues and I am completely stumped at this point so if anyone has any advice I would really appreciate it.

So far I have replaced the stern drive water pump/impeller, new 140 degree t-stat, and a new engine water pump and i'm still seeing the engine temps climb while i'm at idle in the water.

It takes a little bit but the temps will slowly climb up while sitting idling in the water... they have gotten up to about 200 before I shut the boat off or start to cruise. At idle cruising speed or while moving at all the temps almost immediately come back down to around 160F or so.

I'm not sure what else to check at this point?

Ayuh,.... Pull some hoses, 'n See where it's flowin', or not....

Water that gets Into the system, has gotta be able to get Out....

Is the riser clear,..??

 

[sharkin95]

Re: 4.3 Mercruiser operating temps? Overheating?

what type of t-stat housing do you have new design or old ? possibly whats happening is the water circulating in the engine isn't mixing with the incoming cold sea water. clean and check your temp sensor also...

 

[produceguy]

Re: 4.3 Mercruiser operating temps? Overheating?

Might want to check your thermostat. Pretty simple to change out and one more thing to check off the list.

 

[NHGuy]

Re: 4.3 Mercruiser operating temps? Overheating?

I have an 89 Baja with Alpha 1, it creeps up on the temps too. I have written it off to not enough capacity in the impeller to cool the motor at idle. I did cheat when I did my impeller this year, didn't do the base gaskets. That's probably part of the issue. All I have to do is take the motor off idle, maybe 900 or 1000 RPM and it cools right down. It normally runs at 145. Hottest I have seen is 180.
Once you trust the motor just shut it off.
I have and suggest towing insurance, haven't used it yet. It's less cost than a tank of gas if you are an inland boater. It's some good peace of mind.
I had one riser off last month, think I will check the other.

 

[achris]

Re: 4.3 Mercruiser operating temps? Overheating?

The fact that you DON'T have a cooling issue at higher than idle would indicate all the things pointed to above are ok... Those are the items normally associated with high temperature under load, not the other way around...

You need to do an output test on the water pump and put a length of clear hose in and make sure you don't have any bubbles coming through...

Do you have a factory manual? (seloc and clymer are NOT manuals....)

Chris......

 

[stonyloam]

Re: 4.3 Mercruiser operating temps? Overheating?

Chris +1, it may be that you need a new pump housing. If the old housing (plastic right?) is worn or warped by the heat it might be losing efficiency even with the new impeller.

 

[sharkin95]

Re: 4.3 Mercruiser operating temps? Overheating?

make sure you have water in the engine when doing this test. take off your incoming sea water hose from the t-stat housing you should be able to fill a 5 gallon bucket in about 30-45 seconds @ 1500 rpms.

 

[achris]

Re: 4.3 Mercruiser operating temps? Overheating?

Not quite... The output depends on the drive ratio, and it's done as a 15 seconds test at 1000rpm....

If you have 1.84:1, then you should pump 3.3 Qts
If you have 1.62:1, then you should pump 3.6 Qts

Chris......

 

[jimmyc607]

Re: 4.3 Mercruiser operating temps? Overheating?

Took the boat out again Sunday after checking out a few things. I still havent had a chance to do the water test or get an infrared gun though as I was out of town on vacation.

When I did my outdrive water pump I got the full kit and replaced everything including the housing and impeller. I checked the thermo housing and it looks somewhat corroded but nothing horrible. Just to try something I removed the thermostat altogether and tried the boat yesterday... the results we basically the same as the old 140 thermo... while moving temps around around 150 but if you sit idling for a period of time the temps climb up steadily.

 

[ktbarrentine]

Re: 4.3 Mercruiser operating temps? Overheating?

Recommend you follow the instructions of posts 12 and 15. Also, did you test the thermostat when you took it out? (in a pot of water with a thermometer?) Not good to run without the t-stat.... Sounds like you have some blockage, maybe from a previous impeller problem (even before your last one). Power steering? Check your flow.... maybe even take the hose off to the PS cooler and check for pieces of "stuff" blocking passages.

 

[Don S]

Re: 4.3 Mercruiser operating temps? Overheating?

the results we basically the same as the old 140 thermo... while moving temps around around 150 but if you sit idling for a period of time the temps climb up steadily.

That isn't even a meaning full test and tells you nothing. Throwing parts at it and leaving parts out isn't going to help. You need to do the tests or you will playing with this for months.